Nativa, Sinop, v. 9, n. 5, p. 612-627, 2021.

Pesquisas Agrárias e Ambientais

DOI: https://doi.org/10.31413/nativa.v9i5.13168 ISSN: 2318-7670

Solar radiation incidence under different shading screens in tropical climate:

diurnal evolution and estimates

Daniela Roberta BORELLA1, Hercules NOGUEIRA2, Francielli Aloisio MORATELLI3,

Aline KRAESKI3, Adilson Pacheco de SOUZA1,2,3

1 Postgraduate Program in Environmental Physics, Federal University of Mato Grosso, Cuiabá, MT, Brazil.

1 Institute of Agrarian and Environmental Sciences, Federal University of Mato Grosso, Sinop, MT, Brazil.

1 Postgraduate Program in Environmental Sciences, Federal University of Mato Grosso, Sinop, MT, Brazil.

*E-mail: drborella@gmail.com

(ORCID: 0000-0003-2941-2116; 0000-0001-7056-351X; 0000-0002-0304-985X; 0000-0001-5795-9245; 0000-0003-4076-1093)

Submitted on 11/17/2021; Accepted on 12/29/2021; Published on 12/30/2021.

ABSTRACT: The use of photoselective screens improves plant productivity and quality, and it is necessary to

understand the dynamics of solar radiation transmissivity under these microenvironments to subsidize agricultural and

forestry production projects. Therefore, the objective of this work was to describe the diurnal and seasonal evolution

of incidence of global irradiance (IG), photosynthetically active irradiance (IPAR), and luminance in aboveground forest

nurseries under different shading screens. Radiometric fractions were evaluated and statistical equations were obtained

based on the external incidence. Instantaneous measurements of IG, IPAR, and luminance in the exterior and interior of

nurseries (East-West direction), solstices (12/22/2018 and 06/20/2019) and equinoxes (03/21/2019 and

09/21/2019), and local zenithal culminations (02/18/2019 and 10/20/2019) were evaluated between 7h00min and

17h00min. Estimates were evaluated and the data were grouped into two databases composed of 70% and 30%,

respectively, to generate and validate regressions for each variable. The statistical performance of regressions was

evaluated using the following statistical indicators: coefficient of determination (R2), mean square error (MSE), root

mean square error (RMSE), and Willmott index (d). IG, IPAR, and luminance presented similar dynamics of diurnal and

seasonal evolution under the shading screens for external conditions, and the transmissivity was affected by the

environmental conditions (water seasonality and solar declination) and intrinsic characteristics of the shading screens

(porosity and color). The transmission and absorption of IG, IPAR, and luminance were affected by color and porosity

of the shading screens, whereas the reflection was affected only by the color. The values of Willmott index were higher

than 0.9975 and 0.9973 for black screen and photoselective screen, respectively, and were considered as good,

indicating that the equations generated good estimates of IG, IPAR, and luminance for application in different regions.

The choice of shading screens for crops are dependent on spectral composition requirements and IPAR transmissivity

of each species.

Keywords: radiometric properties of photoselective screens; photosynthetically active radiation; irradiance; luminance;

statistical indicators.

Radiação solar incidente sob diferentes telas de sombreamentos em clima

tropical: evolução diurna e estimativas

RESUMO: O uso de telas foto-seletivas melhora a produtividade e qualidade das plantas, e é necessário compreender

a dinâmica da transmissividade da radiação solar sob esses microambientes para subsidiar projetos de produção

agrícolas e florestais. Nesse sentido, o objetivo foi descrever a evolução diurna e sazonal das irradiâncias global (IG),

fotossintéticamente ativa (IPAR) e luminância incidentes em viveiros florestais suspensos sob diferentes telas de

sombreamento. Além disso foram avaliadas as frações radiométricas e obtidas equações estatísticas de estimativas

baseadas na incidência externa. As medidas instantâneas de IG, IPAR e luminância ocorreram no exterior e interior dos

viveiros (alinhados no sentido Leste-Oeste), nos solstícios (22/12/2018 e 22/06/2019), equinócios (21/03/2019 e

21/09/2019) e nas culminações zenitais locais (18/02/2019 e 20/10/2019), entre às 7h00min e 17h00min. Para

avaliação das estimativas, os dados foram agrupados em duas bases, compostas por 70 e 30% para geração e validação

das regressões, para cada variável, respectivamente. Para avaliação do desempenho estatístico das regressões foram

empregados os indicativos estatísticos: coeficiente de determinação (R2), erro absoluto médio (MBE), raiz quadrada

do erro quadrático médio (RMSE) e índice de Willmott (d). IG, IPAR e luminância apresentaram dinâmicas semelhantes

na evolução diurna e sazonal sob as telas de sombreamento em relação as condições externas, sendo a transmissividade

influenciados por condições ambientais (sazonalidade hídrica e declinação solar) e intrínsecas a tela (porosidade e cor).

A transmissão e absorção de IG, IPAR e luminância foram afetadas pela cor e porosidade líquida, enquanto que a reflexão

apenas pela cor. Os valores do índice de Willmott foram superiores a 0,9975 e 0,9973 para as telas pretas e foto-

seletivas, respectivamente, sendo considerado como ótimos, indicando que as equações ajustadas permitem boas

estimativas de IG, IPAR e luminância para aplicação em diferentes regiões. A escolha da tela de sombreamento para o

cultivo de plantas fica dependente das necessidades de composição espectral e transmissividade da IPAR de cada espécie.

Palavras-chave: propriedades radiométricas de telas foto-seletivas; radiação fotossinteticamente ativa; irradiâncias;

luminância; indicadores estatísticos.

Borella et al.

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1. INTRODUCTION

Solar radiation is the main source of energy that regulates

physical, biochemical, and physiological processes of earthly

components; it determines the microclimate, mainly

modulating temperatures, air humidity, and soil moisture, is

responsible for energy exchanges in the water-soil-plant-

atmosphere system, and is essential for ecophysiological

responses of plants, which reflects in crop yields and product

quality.

The availability of energy that reaches the earth surface is

dependent on astronomical (solar declination), atmospheric

(cloudiness, air humidity, and atmospheric turbidity), and

geographical factors that determine spatial and temporal

variations in solar radiation incidence (TERAMOTO et al.,

2019). In addition, the atmosphere composition (gases,

aerosols, water vapor, dust, and particulate matter) affects the

transmissivity of solar radiation, and the clouds are the main

reductors because they absorb specific wavelengths (infrared)

and reflect and diffuse (anisotropically) most solar radiation

(SOUZA, et al., 2016; PALÁCIOS et al., 2018).

The transitional region between the Cerrado and Amazon

biomes in northern state of Mato Grosso, Brazil, has high

mean monthly global radiation, from 16.56 ± 2.82 MJ m-2

day-1 (February, rainiest month in the region) to 21.17 ± 0.83

MJ m-2 day-1 (October), with higher atmospheric

transmissivity and solar radiation in the dry season, between

May and October (SOUZA et al., 2016). It is estimated that

a fraction of this global radiation (40% to 45%) consists of

photosynthetically active radiation (between 400 and 700

nm), which corresponds to a good part of the visible range

of the electromagnetic spectrum (BERGAMASCHI;

BERGONCI, 2017) and is responsible for activating

photosynthetic process in plants (WANG et al., 2015; WU et

al., 2019).

Excess or lack of solar radiation can be harmful to

different groups of plant species; moreover, they affect flows

of latent heat (evapotranspiration) and sensitive heat (air

temperature) (AHMED et al., 2016). Direct incidence of

global solar radiation on plants can cause significant changes

to their biochemical, physiological, and morphogenic

processes (ZHANG; ZHANG, 2017; WU et al., 2019),

oxidative stress, compromised photosynthetic activity and

structural and metabolic changes in chloroplasts are some of

the damage caused by the combination of high light and heat

stress (BALFAGÓN et al., 2019).Therefore, the use of

protected environments for agricultural crops and forest

species in regions of adverse climate conditions has been

increasingly studied, focused on improving yields and quality

of species that present difficulties for production in specific

seasons of the year or regions (HOLCMAN; SENTELHAS,

2012; AHMED et al., 2019; TANG et al., 2020; BORELLA

et al., 2020a).

The use of white plastic screens in greenhouses with

artificial or natural ventilation (AHMED et al., 2019), in

nebulization or evaporative cooling systems (AHMED et al.,

2016), and in energy system with solar photovoltaic modules

(TANG et al., 2020) predominates among the protected crop

systems. However, other plastic materials with different

physical characteristics (chemical composition, porosity,

color, and density) have been used alone or combined with

plastic screens (KOTILAINEN et al., 2018; CHOAB et al.,

2019).

Some ecophysiological studies have investigated

microclimate dynamics and effects of using photoselective

screens (aluminized or thermo reflectors, red, blue, green,

and black) on the growth and development of plants and

found promising results (HOLCMAN; SENTELHAS, 2012;

MONTEIRO et al., 2016; MAHMOOD et al., 2018;

SABINO et al., 2020; BORELLA et al., 2020a,b).

Nevertheless, a better understanding of microclimate

dynamics in these protected environments is important for

different regions and seasons of the year, since the choosing

of the adequate type of screen and percentage of shading

(porosity) is dependent on the species, cultivar, and local

climate conditions (ABDEL-GHANY, 2015; AHMED et al.,

2016; STATUTO et al., 2020).

Information on micrometeorological dynamics within

protected environments is essential for the planning and

development of hydro-agricultural activities, crop

management, and selection of agricultural and forest species

better adapted to local environmental conditions, focusing

on reducing costs, saving water, and increasing production.

The use of shading screens in hot regions decreases the

harmful effects caused by high irradiance on plants

(AHMED et al., 2016; ZHANG; ZHANG, 2017;

BORELLA et al., 2020b), providing a more uniform

distribution of temperature and relative air humidity under

shaded environments (AHMED et al., 2019; BORELLA et

al., 2021), reducing the water vapor pressure deficit (CHOAB

et al., 2019) and, consequently, the water demand of plants

(MONTEIRO et al., 2016; BORELLA et al., 2020a). In

addition, it forms a physical protection barrier against insects-

pest (MAHMOOD et al., 2018). Thus, shading is a simple

and low-cost method regarding implementation and

maintenance (ABDEL-GHANY et al., 2015).

However, controlling climate variables in these

environments is a complex and dynamic process that

depends on external conditions (HOLCMAN;

SENTELHAS, 2012) and a monitoring routine. Moreover,

the implementation costs of monitoring routine systems with

sensors and data acquisition systems (dataloggers) can be

high. Thus, micrometeorological information under

protected environments with no sensors can be obtained by

using simplified statistical models based on weather variables

under full-sun environmental conditions and that allow the

estimation of a variable of interest, such as solar radiation,

with a high degree of accuracy (SOUZA et al., 2017; ROSSI

et al., 2018; TERAMOTO et al., 2019).

Therefore, the objectives of this work were to describe

the diurnal and seasonal evolution, determine the radiometric

ratios, and fit statistic models for estimating global irradiance

(IG), photosynthetically active irradiance (IPAR), and

luminance (Lux) through shading screens with different

physical and spectral characteristics. The evaluations were

carried out in different crop seasons, in a tropical climate

region of Brazil, to obtain tools to subsidize agricultural and

forest production projects.

2. MATERIAL AND METHODS

2.1. Study region and implementation

The study was conducted in a transitional region between

the Cerrado and Amazon biomes, in Sinop, Mato Grosso

(MT), Brazil (11°51'50"S, 55°29'08"W and 384 meters of

altitude). The region presents an Aw climate (tropical hot and

wet), according to the Köppen classification (SOUZA et al.,

Solar radiation incidence under different shading screens in tropical climate: diurnal evolution and estimates

Nativa, Sinop, v. 9, n. 5, p. 612-627, 2021.

614

2013), with mean annual air temperature and relative air

humidity of 25.9 °C and 74.0%, respectively (Figure 1A and

1B). The mean daily global radiation and insolation of the

region are 17.5 to 21.2 MJ m-2 day-1 and 8.2 to 9.7 hours day-

1 in the dry season, and 16.8 to 18.6 MJ m-2 day-1 and 4.9 to

6.3 hours day-1 in the rainy season (Figure 1C).

The climate seasonality of the region is defined by two

hydrological seasons: rainy (October to April) and dry (May

to September) (Figure 1D) (SOUZA et al., 2013). The mean

annual rainfall depth is 1,945.0 mm, which is more than

1,700.0 mm in the spring-summer season, whereas the

reference evapotranspiration range is from 105.0 to 170.0

mm month-1 (3.5 to 5.5 mm day-1) between the rainy and dry

periods in the region (Figure 1D).

The solar radiation components were measured in

aboveground forest nurseries arranged in an East-West

direction, with dimensions of 3.0 × 1.0 × 1.0 m (length,

width, and height), and at 1.0 m above the ground. The full-

sun conditions were used as reference; the top, front, and

lateral sides of the experimental units were covered with

black polyolefin screens with 35%, 50%, 65%, and 80%

shading, thermo-reflector screen (Aluminet®, 50% shading),

and red, blue (Chromatinet®, 50% shading) and green

(Frontinet®, 50% shading) polyolefin screens.

Figure 1. Monthly means and standard deviations for air temperature (A), relative air humidity (B), global radiation and insolation (C),

rainfall and reference evapotranspiration (D) between September 01, 2010 and December 31, 2019 in Sinop, MT, Brazil.

Figura 1. Médias mensais e desvio-padrão da temperatura do ar (A), umidade relativa do ar (B), radiação global e insolação (C), precipitação

e evapotranspiração de referência (D), entre 01/09/2010 e 31/12/2019, em Sinop, MT, Brasil.

2.2. Measurements of IG, IPAR, and Luminance

Instantaneous measurements of incident and reflected

global irradiance (IG – W m-2), photosynthetically active

irradiance (IPAR – μmol m-2 s-1), and luminance (lux) were

measured in the protected environments (nurseries) covered

with shading screens and in the environments at full-sun

conditions. The following sensors were used: i) pyranometer

MP-200 (spectral reading range of 360 to 1,120 nm;

directional response (cosine effect): 5% up to 75° of zenith

angle; temperature response; -0.04 ± 0.04% per °C; response

time: minimum of 1.0 m s-1; non-linearity: below 1% for

measures above 1,750 W m-2); ii) pyranometer MQ-200

(spectral reading range: 410 to 655 nm (considering a

maximum of 50% wavelengths in this range); directional

response (cosine effect): 5% up to 75° of zenith angle;

temperature response; 0.06 ± 0.06% per °C; response time:

minimum of 1.0 m s-1; non-linearity: below 1% for measures

above 3,000 μmol m-2 s-1 of Apogee; and iii) lux meter (LD-

200 - Instrutherm). These sensors were fixed in a leveled

metal platform at 1.50 m height inside and at 0.50 m above

each unit (aboveground nursery).

Solar radiation was measured in the summer solstice

(December 22, 2018) and winter solstice (June 22, 2019),

when the solar declination (δ) is equal to -23.45 and 23.45°;

in the autumnal equinox (March 21, 2019) and spring equinox

(September 21, 2019), when δ = 0°; and in the local zenithal

culmination (𝜙 -11.85°) on February 18, 2019 and October

20, 2019, between 7h00min and 17h00min (local solar time),

in external (above) and internal (inside) conditions of each

aboveground nursery, with maximum intervals of 2 minutes

from each other to minimize the hour angle effects. Three

readings (replications) were carried out for each time of the

day, date, and protected environment.

Jan

Feb

MarApr

May

Jun

Jul

AugSep

Oct

NovDec

100

JanFeb

Mar

Apr

MayJun Jul

AugSepOct

Nov

Dec

Jan

Feb

MarApr

May

Jun

Jul

AugSep

Oct

NovDec

100

150

200

250

300

350

400

450

500

Rainfall Reference evapotranspiration

Months

Rainfall (mm month

-1

)

100

120

140

160

180

200

220

Reference evapotranspiration (mm month

-1

)

Jan

Feb

MarApr

May

Jun

Jul

AugSep

Oct

NovDec

Maximum Mean Minimum

Air temperature (°C)

Air relative humidity (%)

Global radiation

Global radiation (MJ m

-2

day

-1

)

Months

Insolation (hours day

-1

)

Insolation

Borella et al.

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615

The data were analyzed for consistency, and different

values were excluded due to reading errors generated by the

data acquisition system or by atmospheric instability (cloudy

sky), as the case of some times in September and October.

The irradiance at the top of the atmosphere (I0) was obtained

and, then, the coefficient of atmospheric transmissivity (KT)

was determined by the ratio between global irradiance (IG)

and irradiance at the top of the atmosphere (I0).

The transmissivity of IG, IPAR, and luminance under the

polyolefin screens were obtained by the ratio between

readings of the variable inside and outside the protected

environments. The percentage of transmission, reflection,

and absorption of the irradiances were calculated based on

the incident and reflected data found for each shading screen.

2.3. Statistical models to estimate IG, IPAR, and

luminance

The hourly instantaneous values of IG, IPAR, and

luminance in shading conditions were grouped into two

databases: one with 70% of the total data for calibration of

statistical coefficients of models (with dates of December 22;

March 21; September 21, and October 20), and other with

30% of the data for validation of statistical performance of

estimation models (with the dates of February 18 and June

22). Simple linear regressions (y = a + b x) were used between

internal IG, IPAR, and luminance (dependent variable) and

external IG, IPAR, and luminance (independent variable) for

each shading condition.

The statistical performance of the generated models was

evaluated using the following indicators: mean square error

(MSE) (Eq. 1), root mean square error (RMSE) (Eq. 2) and

fit of the Willmott index (dw) (Eq. 3) (SOUZA et al., 2017).

MSE = ∑ |  |



  (01)

𝑅MSE = 󰇣∑( )



 󰇤. (02)

𝑑w = 1 − ∑( )





∑(|󰆒 

| |󰆒 

|)



 (03)

where: 𝑃 is the estimated values; 𝑂 is the measured values; 𝑛 is the

number of observations; |𝑃′ | is the absolute value of the

difference 𝑃′− 𝑂

; and |𝑂′| is the absolute value of the difference

𝑂′− 𝑂

.

The fractions of IPAR and luminance (independent

variable) in relation to IG (variable dependent) were

determined using linear regressions with grouping of data

from black screens with different porosities and from

photoselective screens with the same porosity.

3. RESULTS

The atmospheric conditions in the zenithal culmination

dates for the latitude -11.85° are presented in the Table 1.

There was 0.2 mm rainfall at the evening of October 20,

2019, when the atmospheric transmissivity was lower than

0.35, i.e., a cloudy sky (ESCOBEDO et al., 2009). This

atmospheric condition hindered the instantaneous

measurements of IG, IPAR, and luminance between 15h00min

and 17h00min in that date (Figures 2 to 4K-L).

Table 1. Daily rainfall, air temperature, relative air humidity, global radiation, and insolation in different dates of solar declination, in Sinop,

MT, Brazil.

Tabela 1. Valores diários de precipitação, temperatura do ar, umidade relativa do ar, radiação global e insolação nas diferentes datas de

declinação solar, em Sinop, MT, Brasil.

Date Rainfall Air temperature (°C) Relative air humidity (%) Global radiation Insolation

(mm) Mean

Maximum Minimum Mean

Maximum Minimum (MJ m-2 d-1) (hours)

12/22/2018

0 27.55 36.50 21.50 71.19 95.00 34.00 18.67 7.10

02/18/2019 0 25.81 32.46 21.56 83.50 99.20 49.94 20.85 9.30

03/21/2019

0 26.20 33.29 22.23 87.10 97.72 60.81 14.65 5.00

06/22/2019

0 29.94 34.66 20.43 46.80 94.94 32.94 17.65 10.40

09/21/2019 0 28.35 38.97 22.45 63.87 94.94 32.94 15.72 5.80

10/20/2019 0.2 27.49 35.74 22.35 71.98 94.90 39.70 17.74 5.30

3.1. Diurnal and seasonal evolution of solar radiation

through shading screens

The global and photosynthetically active irradiances and

the luminance presented similar dynamics throughout the

day, regardless of the microenvironment (full-sun conditions

and under shading screens) and the different solar

declinations for the same latitude (-11.85°). The highest

peaks of incidence of solar radiation occurred by 12h00min

and the lowest at sunrise and sunset, 07:00 and 17h00min,

respectively (Figures 2, 3, and 4), due to variations in the

zenith angle.

The highest incident energy levels in full-sun conditions

at approximately the solar mid-day (IG > 1000 W m-2, IPAR >

2000 μmol m-2 s-1, and luminance > 60.000 lux) were found

during the rainy season, in the summer solstice, autumnal

equinox, and at the local solar culmination, whereas the

lowest energy levels were found in the dry and dry-rainy

seasons (winter solstice and spring equinox, respectively).

The increase in black polyolefin screen shading level

gradually decreased the IG, IPAR, and luminance inside the

microenvironments in all dates (declinations) considered in

this study. Contrastingly, in the qualitative analysis, the black

polyolefin screen, thermo-reflector screen, and red, blue, and

green polyolefin screens, all with 50% shading, presented

similar IG transmissivity values; a higher transmissivity of IPAR

and luminance was found for the black polyolefin screen

when compared to the other colored screens with the same

shading percentage (Figures 3 and 4).

3.2. Solar radiation transmission, reflection, and

absorption through shading screens

The values of coefficient of atmospheric transmissivity

(KT) of global radiation ranged from 0.43 in October to 0.69

in February (rainy season), and from 0.67 in June to 0.54 in

September (dry season), confirming the results of Souza et al.

(2016), who found intervals of monthly KT ranging from 0.43

Solar radiation incidence under different shading screens in tropical climate: diurnal evolution and estimates

Nativa, Sinop, v. 9, n. 5, p. 612-627, 2021.

616

to 0.56 in the rainy season and from 0.54 to 0.64 in the dry

season, for this same region. The variations in mean daily

global radiation (Table 1) and KT (Table 2) found for the

evaluation dates (February 18, 2019 and October 20, 2019),

corresponding to zenithal culmination and the period rainy

season, were strongly affected by atmospheric instability

(cloudiness) at the time of the instantaneous measurements.

Figure 2. Diurnal and seasonal evolution of irradiance at the top of the atmosphere and global irradiance under increasing levels of shading

(left) and spectral solar radiation (right), in Sinop, MT, Brazil.

Figura 2. Evolução diurna e sazonal das irradiâncias do topo da atmosfera e global sob níveis crescentes de sombreamento (à esquerda) e

espectrais (à direita) da radiação solar, em Sinop, MT, Brasil.

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MAX

FS = 1,168

Irradiance (W m

-2

)

Time of day (h)

Irradiance (W m

-2

)

Time of day (h)

MAX

FS = 1,108

02/18/2019 12/22/2018

Irradiance (W m

-2

)

Time of day (h)

Irradiance (W m

-2

)

Time of day (h)

MAX

FS = 1,110

03/21/2019

Irradiance (W m

-2

)

Time of day (h)

Irradiance (W m

-2

)

Time of day (h)

MAX

FS = 770

06/22/2019

Irradiance (W m

-2

)

Time of day (h)

Irradiance (W m

-2

)

Time of day (h)

MAX

FS = 989

09/21/2019

Irradiance (W m

-2

)

Time of day (h)

Irradiance (W m

-2

)

Time of day (h)

MAX

FS = 1,086

10/20/2019

Top of the atmosphere Full sun Black 35% Black 50% Black 65% Black 80%

Irradiance (W m

-2

)

Time of day (h)

Thermo-reflector 50% Red 50% Blue 50% Green 50%

Irradiance (W m

-2

)

Time of day (h)

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Figure 3. Diurnal and seasonal evolution of photosynthetically active irradiance under increasing levels of shading (left) and spectral solar

radiation (right), in Sinop, MT, Brazil.

Figura 3. Evolução diurna e sazonal da irradiância fotossintéticamente ativa sob níveis crescentes de sombreamento (à esquerda) e espectrais

(à direita) da radiação solar, em Sinop, MT, Brasil.

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3000

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500

1000

1500

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3000

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1000

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3000

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3000

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3000

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500

1000

1500

2000

2500

3000

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500

1000

1500

2000

2500

3000

IMAXFS = 2,635

IPAR (μmol m-2 s-1)

Time of day (h)

IPAR (μmol m-2 s-1)

Time of day (h)

IMAXFS = 2,617

IPAR (μmol m-2 s-1)

Time of day (h)

IPAR (μmol m-2 s-1)

Time of day (h)

IMAXFS = 2,562

06/22/2019

IPAR (μmol m-2 s-1)

Time of day (h)

IPAR (μmol m-2 s-1)

Time of day (h)

IMAXFS = 1,829

IPAR (μmol m-2 s-1)

Time of day (h)

IPAR (μmol m-2 s-1)

Time of day (h)

IMAXFS = 2,114

IPAR (μmol m-2 s-1)

Time of day (h)

IPAR (μmol m-2 s-1)

Time of day (h)

IMAXFS = 2,418

10/20/2019 09/21/2019 03/21/2019 02/18/2019 12/22/2018

IPAR (μmol m-2 s-1)

Time of day (h)

Full sun Black 35% Black 50% Black 65% Black 80%

IPAR (μmol m-2 s-1)

Time of day (h)

Thermo-reflector 50% Red 50% Blue 50% Green 50%

Solar radiation incidence under different shading screens in tropical climate: diurnal evolution and estimates

Nativa, Sinop, v. 9, n. 5, p. 612-627, 2021.

618

Figure 4. Diurnal and seasonal evolution of luminance under increasing levels of shading (left) and spectral solar radiation (right), in Sinop,

MT, Brazil.

Figura 4. Evolução diurna e sazonal da luminância sob níveis crescentes de sombreamento (à esquerda) e espectrais (à direita) da radiação

solar, em Sinop, MT, Brasil.

The transmissivity of IG, IPAR, and luminance found for

the protected environments covered with black polyolefin

screens of 35%, 50%, 65%, and 80% shading decreased as

the shading level was increased, regardless of the solar

declination. Consequently, the increase in shading level

decreased the transmission and reflection due to the increase

in absorption of IG, IPAR, and luminance (Table 2 and Figure

5).

7 8 9 10 11 12 13 14 15 16 17

15000

30000

45000

60000

75000

90000

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15000

30000

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60000

75000

90000

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30000

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30000

45000

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90000

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15000

30000

45000

60000

75000

90000

MAX

FS = 76,200

10/20/2019 09/21/2019 06/22/2019 03/21/2019 02/18/2019 12/22/2018

Luminance (lux)

Time of day (h)

Luminance (lux)

Time of day (h)

MAX

FS = 72,400

Luminance (lux)

Time of day (h)

Luminance (lux)

Time of day (h)

MAX

FS = 75,200

Luminance (lux)

Time of day (h)

Luminance (lux)

Time of day (h)

MAX

FS = 49,167

Luminance (lux)

Time of day (h)

Luminance (lux)

Time of day (h)

MAX

FS = 57,467

Luminance (lux)

Time of day (h)

Luminance (lux)

Time of day (h)

MAX

FS = 65,067

Luminance (lux)

Time of day (h)

Full sun Black 35% Black 50% Black 65% Black 80%

Luminance (lux)

Time of day (h)

Thermo-reflector 50% Red 50% Blue 50%

Green 50%

Borella et al.

Nativa, Sinop, v. 9, n. 5, p. 612-627, 2021.

619

Regarding the photoselective (colored) screens with 50%

shading, the mean transmissivities of irradiance were 0.4216,

0.3169, 0.3250, 0.3210, and 0.3524 for the black, thermo-

reflector, red, blue, and green screens, respectively. Black

screen with 50% shading presented higher transmission

(42.16%) and lower reflection (4.23%) of IG, IPAR, and

luminance than thermo-reflector, red, blue, and green

screens, except for the IG in the red screen in (44.00%).

The thermo-reflector screen (as commercially described)

presented the highest reflection (22.50%) and the lowest

absorption, regardless of the season. The red screen

presented the lowest absorbed IG (34.29%); contrastingly, it

was the screen that presented the highest absorption levels of

IPAR and luminance, together with the blue screen.

Table 2. Daily mean values of coefficients of transmission, reflection, and absorption of solar irradiance in polyolefin screens in relation to

atmospheric conditions in different dates of solar declination, in Sinop, MT, Brazil.

Tabela 2. Valores médios diários dos coeficientes de transmissão, reflexão e absorção das irradiâncias solares de telas poliefinas com relação

à condição atmosférica nas diferentes datas de declinação solar, em Sinop, MT, Brasil.

Date KT KTt35% KTt50% KTt65% KTt80% KTttr50% KTtvm50% KTtaz50% KTtvd50%

Global radiation

12/22/2018 0.72

02/18/2019 0.69

03/21/2019 0.70

06/22/2019 0.67

09/21/2019 0.54

10/20/2019 0.43

Transmission 0.6240

0.5368

0.4215

0.2743

0.1575

0.3402

0.4399

0.3792

0.3944

Reflection -

0.0726

0.0569

0.0478

0.0473

0.2559

0.2172

0.1507

0.1121

Absorption -

0.3907

0.5216

0.6778

0.7951

0.4039

0.3429

0.4701

0.4935

Photosynthetically active radiation

12/22/2018 -

0.51

0.43

0.24

0.14

0.34

0.30

0.36

0.35

02/18/2019 -

0.53

0.42

0.27

0.13

0.32

0.30

0.38

03/21/2019 -

0.50

0.36

0.23

0.12

0.28

0.26

0.28

0.34

06/22/2019 -

0.50

0.38

0.25

0.13

0.24

0.20

0.21

0.23

09/21/2019 -

0.52

0.43

0.26

0.17

0.31

0.28

0.27

0.28

10/20/2019 -

0.56

0.44

0.30

0.17

0.32

0.30

0.31

0.33

Transmission -

0.5226

0.4111

0.2602

0.1429

0.2999

0.2737

0.2889

0.3186

Reflection -

0.0405

0.0302

0.0273

0.0279

0.2065

0.1002

0.0534

0.1740

Absorption -

0.4369

0.5587

0.7125

0.8292

0.4936

0.6261

0.6577

0.5074

Luminance

12/22/2018 -

0.53

0.44

0.26

0.14

0.35

0.28

0.34

0.37

02/18/2019 -

0.54

0.44

0.28

0.14

0.33

0.29

0.30

0.40

03/21/2019 -

0.52

0.40

0.26

0.13

0.28

0.27

0.31

0.37

06/22/2019 -

0.52

0.43

0.30

0.16

0.24

0.20

0.22

0.28

09/21/2019 -

0.55

0.45

0.29

0.19

0.32

0.26

0.28

0.31

10/20/2019 -

0.57

0.45

0.30

0.19

0.34

0.27

0.31

0.34

Transmission -

0.5376

0.4322

0.2810

0.1577

0.3105

0.2613

0.2949

0.3443

Reflection -

0.0480

0.0397

0.0367

0.0357

0.2123

0.0884

0.0564

0.0674

Absorption -

0.4144

0.5281

0.6822

0.8066

0.4773

0.6503

0.6488

0.5883

where: KT is the coefficient of atmospheric transmissivity; KTt35%, KTt50%, KTt65%, KTt80%, KTttr50%, KTtvm50%, KTtaz50%, and KTtvd50% are coefficients of

transmissivity for black polyolefin screens with 35%, 50%, 65%, and 80% shading, and thermo-reflector, red, blue, and green screens, respectively.

em que: KT é o coeficiente de transmissividade atmosférica; KTt35%, KTt50%, KTt65%, KTt80%, KTttr50%, KTtvm50%, KTtaz50% e KTtvd50% são os coeficientes de

transmissividade das telas poliefinas pretas de 35, 50, 65 e 80% de sombreamento, termorefletora, vermelha azul e verde, respectivamente.

3.3. Estimates of IG, IPAR, and luminance under the

shading screens

The linear regressions used to estimate IG, IPAR, and

luminance under the protected environments covered with

polyolefin screens presented coefficients of determination

(R²) higher than 80% for the three variables and in all shading

screens evaluated (Figures 6 and 7).

In general, the equations used for the estimates under

screens black presented underestimates (negative MSE

values), however, lower than 1% of the mean values for each

variable. The black screens with 50% and 65% shading

presented the highest deviations and, consequently, higher

spreading (RMSE) for the estimates of the three irradiances

(Figure 6). In the thermo-reflector, blue, and red screens, the

equations generated overestimates (positive MSE values),

except for IG and IPAR in the red screen and for all irradiances

in the green screen. The spreading (RMSE) was observed in

estimates for the 50% thermo-reflector screen (Figure 7). The

Willmott index was higher than 0.9975 and 0.9973 for the

black and photoselective screens, respectively.

The mean fractions of IPAR and luminance in relation to

IG in the black screens with increasing shading levels were

44.80% and 1.55%, respectively (Figures 8A, B). The

fractions of irradiance in the black screens were similar, thus,

they were not presented separately in this study. In general,

these fractions for photoselective screens were

approximately 52.60 and 1.85% (Figure 8C, D); however,

when analyzed separately, it presented variations in fractions

of IPAR (44.88 to 68.70%) and luminance (1.56 to 2.62%)

from the black to the red screen (Table 3).

Solar radiation incidence under different shading screens in tropical climate: diurnal evolution and estimates

Nativa, Sinop, v. 9, n. 5, p. 612-627, 2021.

620

Figure 5. Percentage of transmission, reflection, and absorption of global and photosynthetically active radiations and luminance under

different shading screens, in Sinop, MT, Brazil.

Figura 5. Percentuais de transmissão, reflexão e absorção da radiação global, radiação fotossinteticamente ativa e luminância sob diferentes

telas de sombreamento, em Sinop, MT, Brasil.

Table 3. Linear equations to estimate fractions of photosynthetically active radiation (IPAR) and luminance in relation to global solar radiation

(IG) for photoselective screens, in Sinop, MT, Brazil.

Tabela 3. Equações lineares de estimativas da fração da radiação fotossinteticamente ativa (IPAR) e da luminância em relação a radiação solar

global (IG) nas telas foto-seletivas, em Sinop, MT, Brasil.

Shading screen Variables Linear equations Correlation coefficient (R²)

Black 50% IPAR IG = 0.44876 IPAR 0.99586

Luminance IG = 0.01559 luminance 0.99425

Thermo-reflector 50% IPAR IG = 0.48248 IPAR 0.9839

Luminance IG = 0.01711 luminance 0.98765

Red 50% IPAR IG = 0.68695 IPAR 0.99215

Luminance IG = 0.02616 luminance 0.98719

Blue 50% IPAR IG = 0.55929 IPAR 0.9938

Luminance IG = 0.02014 luminance 0.99525

Green 50% IPAR IG = 0.53496 IPAR 0.99038

Luminance IG = 0.01825 luminance 0.99209

4. DISCUSSION

The IG, IPAR, and luminance presented similar dynamics

in the diurnal and seasonal evolution under the shading

screens in relation to environmental conditions (full sun). In

the diurnal evolution, the highest peak of incidence of these

irradiances occurred at approximately the solar mid-day due

to the lower angle of incidence (zenith angle) of solar rays on

the surface, increasing the availability of energy per unit of

area (BERGAMASCHI; BERGONCI, 2017).

The inflections of transmissivity values found

approximately at sunrise and sunset occur due to the

predominance of diffuse radiation (fraction of radiation not

measured in this study). The plastic screens present similar

radiometric properties to those of translucid materials

(plastic), presenting a high transmittance of diffuse radiation,

although the structure of plastic materials is not

homogeneous (AL-HELAL; ABDEL-GHANY, 2010).

The temporal evolution of global irradiance follows the

irradiance variations at the top of the atmosphere, and the

seasonality is affected by solar declination and atmospheric

dynamics (TERAMOTO et al., 2019). The highest

transmissivity and fluctuations of IG, IPAR, and luminance

occurred during the rainy season (summer-autumn), which is

connected to the cloudiness dynamics at this latitude and

season of the year. In this case, atmospheric instability occurs

during the rainy season because of a high cloud density and

water vapor concentration, reducing global radiation by

reflection, absorption, and diffusion before it reaches the

ground surface, which decreases the direct incidence of

global radiation and indicates predominance of diffuse

Photosynthetically active radiation

Transmission (%)

Global radiation Luminance

Transmission (%)

Reflection (%)

Black 35%

Black 50%

Black 65%

Black 80%

Termo-reflective 50%

Red 50%

Blue 50%

Green 50%

Absorption (%)

Black 35%

Black 50%

Black 65%

Black 80%

Termo-reflective 50%

Red 50%

Blue 50%

Green 50%

Absorption (%)

Shading screens

Black 35%

Black 50%

Black 65%

Black 80%

Termo-reflective 50%

Red 50%

Blue 50%

Green 50%

Absorption (%)

Borella et al.

Nativa, Sinop, v. 9, n. 5, p. 612-627, 2021.

621

radiation (ZAMADEI et al., 2021). This anisotropic

dynamics of interaction of solar radiation with the

atmosphere makes only a part of the solar radiation to be

transmitted to the ground surface (SOUZA et al., 2016), thus

explaining the fluctuations of IG, IPAR, and luminance under

full-sun conditions and under shading screens over the day

and the year (Figures 2 a 4).

Larger number of days with atmospheric transmissivity

higher than 55% (open sky days with predominance of direct

radiation) and lower oscillations of global radiation occur in

the dry season (ZAMADEI et al., 2018) and, consequently,

lower photosynthetically active radiation and luminance.

However, the low atmospheric transmissivity and insolation

found on September 21 (Tables 1 and 2) can be explained by

the high concentration of aerosols present in the atmosphere

due to high indexes of fires that occur during the dry season

in the region (PALÁCIOS et al., 2018).

Figure 6. Linear equations for the estimates and their statistical indicators of global irradiance (IG) photosynthetically active irradiance (IPAR),

and luminance under black polyolefin screens with different shading levels, in Sinop, MT, Brazil.

Figura 6. Equações lineares de estimativas e seus indicadores estatísticos das irradiâncias global (IG), fotossinteticamente ativa (IPAR) e

luminância, sob telas poliefinas pretas com diferentes níveis de sombreamento, em Sinop, MT, Brazil.

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LuminancePhotosynthetically active radiation

Y = -7.8146 + 0.5622 X

= 0.9222

MBE = 3.16

RMSE = 28.63

dw = 0.9995

internal black 35% (W m

-2

)

external black 35% (W m

-2

)

Global radiation

Y = -44.3352 + 0.5645 X

= 0.9704

MBE = -6.34

RMSE = 57.56

dw = 0.9997

PAR

internal black 35% (μmol m

-2

-1

)

PAR

external black 35% (μmol m

-2

-1

)

Y = -146.4440 + 0.5507 X

= 0.9827

MBE = -117.66

RMSE = 1466.43

dw = 0.9997

Luminance internal black 35% (lux)

Luminance external black 35% (lux)

internal black 50% (W m

-2

)

external black 50% (W m

-2

)

Y = -34.0885 + 0.4899 X

= 0.9678

MBE = -3.10

RMSE = 35.24

dw = 0.9990

Y = -52.4609 + 0.4611 X

= 0.9571

MBE = -4.79

RMSE = 88.82

dw = 0.9988

PAR

internal black 50% (μmol m

-2

-1

)

PAR

external black 50% (μmol m

-2

-1

)

Y = -1556.4737 + 0.4776 X

= 0.9704

MBE = -396.99

RMSE = 2516.25

dw = 0.9987

Luminance internal black 50% (lux)

Luminance external black 50% (lux)

Y = -35.7548 + 0.3341 X

= 0.8189

MBE = -13.90

RMSE = 41.14

dw = 0.9975

internal black 65% (W m

-2

)

external black 65% (W m

-2

)

Y = -81.0584 + 0.3240 X

= 0.8021

MBE = -21.54

RMSE = 83.42

dw = 0.9978

PAR

internal black 65% (μmol m

-2

-1

)

PAR

external black 65% (μmol m

-2

-1

)

Y = -1730.4031 + 0.3268 X

= 0.8419

MBE = -719.45

RMSE = 1782.03

dw = 0.9987

Luminance internal black 65% (lux)

Luminance external black 65% (lux)

Y = -31.3416 + 0.2191 X

= 0.9297

MBE = -2.66

RMSE = 20.66

dw = 0.9985

internal black 80% (W m

-2

)

external black 80% (W m

-2

)

Y = -84.2672 + 0.2177 X

= 0.9284

MBE = -3.11

RMSE = 47.40

dw = 0.9985

PAR

internal black 80% (μmol m

-2

-1

)

PAR

external black 80% (μmol m

-2

-1

)

Y = -2058.7493 + 0.2167 X

= 0.8819

MBE = -88.66

RMSE = 1222.23

dw = 0.9987

Luminance internal black 80% (lux)

Luminance external black 80% (lux)

Solar radiation incidence under different shading screens in tropical climate: diurnal evolution and estimates

Nativa, Sinop, v. 9, n. 5, p. 612-627, 2021.

622

Figure 7. Linear Equations for the estimates and their statistical indicators of global irradiance (IG), photosynthetically active irradiance

(IPAR), and luminance under photoselective polyolefin screens with 50% of shading, in Sinop, MT, Brazil.

Figura 7. Equações lineares de estimativas e seus indicadores estatísticos das irradiâncias global (IG), fotossintéticamente ativa (IPAR) e

luminância, sob telas poliefinas foto-seletivas com 50% de sombreamento, em Sinop-MT.

In general, the intensity and distribution of solar radiation

on the earth surface can be affected by factors in global scale

(atmosphere composition, structure, and interaction, solar

declination, and zenith angle) and regional scale (seasons of

the year, latitude, altitude, slope, land position, atmosphere

optical thickness, vegetation, soil, and continentality)

(BERGAMASCHI; BERGONCI, 2017).

Global radiation interacts with materials in the Earth's

surface, generating different dynamics of their properties

that, combined with atmospheric effects, latitude, and season

of the year, affect the seasonality of the incident and available

radiation. Among these surface physical characteristics, The

structure size, shape, position, and architecture, the material

composition, porosity, roughness, texture, angle of exposure,

aging, and degradation, the shading screen color and bright

and radiometric property, and the water and dust deposited

on the material also affect the transmission, reflection, and

0 250 500 750 1000 1250

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Photosynthetically active radiation

Y = -32.6898 + 0.4158 X

= 0.9012

MBE = 18.29

RMSE = 46.57

dw = 0.9978

internal thermo-reflector (W m

-2

)

external thermo-reflector (W m

-2

)

Y = -85.6484 + 0.3806 X

= 0.9354

MBE = 2.82

RMSE = 110.41

dw = 0.9975

PAR

internal thermo-reflector (μmol m

-2

-1

)

PAR

external thermo-reflector (μmol m

-2

-1

)

Luminance

Y = -1822.6179 + 0.3755 X

= 0.9086

MBE = 1044.44

RMSE = 3052.95

dw = 0.9973

Luminance internal thermo-reflector (lux)

Luminance external thermo-reflector (lux)

Y = -71.9579 + 0.5740 X

= 0.9395

MBE = -2.87

RMSE = 28.61

dw = 0.9995

internal screen red (W m

-2

)

external screen red (W m

-2

)

Y = -113.4947 + 0.3740 X

= 0.9473

MBE = -5.15

RMSE = 54.15

dw = 0.9992

PAR

internal screen red (μmol m

-2

-1

)

PAR

external screen red (μmol m

-2

-1

)

Y = -2876.3506 + 0.3466 X

= 0.9542

MBE = 84.28

RMSE = 2471.18

dw = 0.9974

Luminance internal red (lux)

Luminance external red (lux)

Y = -18.0227 + 0.4363 X

= 0.9130

MBE = 8.09

RMSE = 43.23

dw = 0.9983

internal screen blue (W m

-2

)

external blue (W m

-2

)

Y = -55.3925 + 0.3564 X

= 0.9383

MBE = 9.78

RMSE = 76.94

dw = 0.9984

PAR

internal screen blue (μmol m

-2

-1

)

PAR

external screen blue (μmol m

-2

-1

)

Y = -1833.0285 + 0.3645 X

= 0.9472

MBE = 621.29

RMSE = 2187.92

dw = 0.9982

Luminance internal blue (lux)

Luminance external blue (lux)

Y = -53.2888 + 0.5069 X

= 0.9534

MBE = -0.66

RMSE = 43.18

dw = 0.9988

internal screen green (W m

-2

)

external screen green (W m-2)

Y = -114.8941 + 0.4193 X

= 0.9234

MBE = -29.23

RMSE = 81.31

dw = 0.9988

PAR

internal screen green (μmol m-2 s-1)

PAR

external screen green (μmol m

-2

-1

)

Global radiation

Y = -4012.4020 + 0.4559 X

= 0.9377

MBE = -898.28

RMSE = 2541.07

dw = 0.9986

Luminance internal green (lux)

Luminance external green (lux)

Borella et al.

Nativa, Sinop, v. 9, n. 5, p. 612-627, 2021.

623

absorption of solar radiation under shading screens

(ABDEL-GHANY et al., 2015; CHOAB et al., 2019).

The spectral transmittance of black screens with different

shading levels or porosity was directly proportional the

screens porosity (Figure 5). Thus, the direct passage of solar

radiation by the screen pores is dependent on its porosity

(AL-HELAL; ABDEL-GHANY, 2010). Given the same

porosity of the photoselective screens, the black screen

presents higher transmittance than the other screens,

denoting the higher effect of the screen color over the

porosity on the transmittance of IG, IPAR, and luminance.

Similar dynamics of spectral transmittance were found

under environmental conditions by Al-Helal; Abdel-Ghany

(2010) and Sabino et al. (2020). Holcman; Sentelhas (2012)

and Abdel-Ghany et al. (2015) found lower transmission for

HG and HPAR in colored screens of same porosity under

greenhouse conditions (Table 4). In addition to the strong

effect of the solar radiation incidence angle and color and

porosity of plastic screens (AL-HELAL; ABDEL-GHANY,

2010), the configuration of the structure and local climate can

significantly reduce or increase the solar radiation

transmissivity (MAHMOOD et al., 2018).

The reflectance of IG, IPAR, and luminance on the black

screens with different porosities were low and proportional

to the shading level; the opposite was found for the

photoselective screens with similar porosities, since in this

case, thermo-reflector, red, blue, and green screens presented

higher reflectance than the black screen (Figure 5).

Higher reflectance of IPAR were found for the thermo-

reflector and green screens. The same result was reported by

Al-Helal; Abdel-Ghany (2010) and Abdel-Ghany et al. (2015)

(Table 4). Abdel-Ghany et al. (2015) reported that the high

reflectance of solar radiation, combined with high absorption

and emission of infrared thermal radiation (86.6%) of

thermo-reflector screens, makes this material very useful to

improve the energy balance of a greenhouse.

Figure 8. Linear equations for the estimates of fraction of photosynthetically active irradiance (IPAR) and luminance in relation to global solar

irradiance (IG) under black screen (A and B) and photoselective screen (C and D).

Figura 8. Equações lineares de estimativas da fração da radiação fotossintéticamente ativa (IPAR) e da luminância em relação a radiação solar

global (IG) nas telas pretas (A e B) e foto-seletivas (C e D).

According to Al-Hela; Abdel-Ghany (2010), the color

brightness of shading screens has more effect on reflectance

than its porosity, because a bright color screen reflects most

of the incident HPAR, i.e., the electromagnetic waves in this

spectrum range, whereas a dark color screen reflects the

incident HPAR only on the screen color spectrum band and

absorbs the incident HPAR in the complementary remaining

color spectrum.

The absorptions of IG, IPAR, and luminance by black

shading screens were inversely proportional to the screen

porosity. Abdel-Ghany et al. (2015) found that black screens

with 70% shading in a greenhouse present approximately

68% absorption of HG and HPAR, since plastic screens with

dark colors and lower porosity significantly increase the solar

radiation absorption capacity, mainly the photosynthetically

active radiation.

Considering a same porosity, red and blue screens present

higher IPAR absorption capacity, which is more than 10%

when compared to the other screens; whereas thermo-

reflector and green screens reflected 10% more IPAR than the

other screens. The color and brightness of plastic screens had

significant effects on transmission, reflection, and absorption

of IG, IPAR and luminance. Al-Helal; Abdel-Ghany (2010)

found that most transmitted and reflected photosynthetically

active radiation may have origin in the spreading of the screen

texture, which depends on the color. Solar radiation

0 250 500 750 1000 1250 1500 1750

150

300

450

600

750

900

0 10000 20000 30000 40000 50000

150

300

450

600

750

900

0 250 500 750 1000 1250 1500 1750

150

300

450

600

750

900

0 10000 20000 30000 40000 50000

150

300

450

600

750

900

= 0.44798 I

PAR

= 0.99374

Black 35% Black 50% Black 65% Black 80%

(W m

-2

)

PAR

(μmol m

-2

-1

)

= 0.01549 luminance

= 0.99129

(W m

-2

)

Luminance (lux)

= 0.52633 I

PAR

= 0.96942

Thermo-reflector 50% Red 50% Blue 50% Green 50%

(W m

-2

)

PAR

(μmol m

-2

-1

)

= 0.01853 luminance

= 0.95975

(W m

-2

)

Luminance (lux)

Solar radiation incidence under different shading screens in tropical climate: diurnal evolution and estimates

Nativa, Sinop, v. 9, n. 5, p. 612-627, 2021.

624

absorption also depends on the incident solar energy flow

and radiation incidence angle on the target

(BERGAMASCHI; BERGONCI, 2017).

The HPAR represents 40% to 45% of the HG, varying

according to the atmospheric conditions (mainly cloudiness)

and to the incidence angle, which varies according to the

season of the year, latitude, and hour of the day

(BERGAMASCHI; BERGONCI, 2017). The increase in the

shading level of black screens decreased the quantity, but not

the quality of the IPAR transmitted by the screens, reaching

approximately 45% internal IG (Figure 8). The screen color

affected considerably the proportion of IPAR and luminance

inside the IG. The red screen (68.70%) presented more of

20% in the proportion of the IPAR for the black screen

(44.88%) and thermo-reflector screen (48.25%) and 13%

more than the blue (55.93%) and green screens (53.50%)

(Table 3).

Holcman; Sentelhas (2012) found proportions of 30%,

29%, 20%, and 17% of HPAR on the HG in black, thermo-

reflector, red, and blue screens, respectively, all those with

70% shading under greenhouse conditions. The quality of

radiation is the variation of distribution of radiant energy in

different wavelengths; this variation occurs with the use of

different colors and textures of plastic materials as shading

(ABDEL-GHANY et al., 2015).

Table 4. Percentage of transmission, reflection, and absorption of radiation components by different shading screens, obtained in a literature

review, for different places and periods of the year.

Tabela 4. Percentuais de transmissão, reflexão e absorção de componentes da radiação por diferentes telas de sombreamento obtidas em

revisão de literatura, para diferentes localidades e períodos do ano.

Localization Estructure Shading screen Transmission (%) Reflection (%) Absorption (%) literature review

Saudi

Arabia/Arid

climate (BWh) -

Latitude 24° 39' N and

longitude 46° 47' E

(December/2008 at

February/2009)

Winter

Full sun and

oriented in a

East-West

direction.

Black 50% 47.0 HPAR 8.0 HPAR 45.0 HPAR

Al-Helal and

Abdel-Ghany

(2010)

Green 50% 43.0 HPAR 11.0 HPAR 46.0 HPAR

Dark green 80% 19.0 HPAR 6.0 HPAR 75.0 HPAR

Blue 80% 29.0 HPAR 10.0 HPAR 61.0 HPAR

Brazil/Subtropical

climate (Cwa) -

latitude 22° 42' 40" S,

longitude 47° 37' 30"

W and altitude of 546

m (December/2005 at

June/2006)

Summer and Autumn

Greenhouse

covered with

transparent low-

density

polyethylene

(LDPE) of

thickness 0.15

mm.

Black 70% 10.4 HG

Holcman and

Sentelhas

(2012)

7.0 HPAR

Thermo-reflective

70%

13.6 HG

8.4 HPAR

Red 70% 27.0 HG

12.0 HPAR

Blue 70% 22.9 HG

8.8 HPAR

Saudi Arabia/Arid

climate (BWh) -

Latitude 24° 39' N and

longitude 46° 47' E

(18 at 26 of

December/2014)

Winter

Greenhouse

covered with

polycarbonate

sheet of 8.15 mm

thickness and

oriented in a

North-South

direction.

Black 70% 26.1 HG 3.5 HG 68.6 HG

Abdel-Ghany et

al. (2015)

26.6 HPAR 3.7 HPAR 68.8 HPAR

Thermo-reflective

85%

13.4 HG 55.2 HG 18.7 HG

12.8 HPAR 55.4 HPAR 18.3 HPAR

Brazil/tropical hot

and humid climate

(Aw) - Latitude

11.85°S, longitude

55.56°W and altitude

of 371m (July/2015 at

April/2016)

From Winter to

Autumn

Full sun and

oriented in a

North-South

direction.

Black 35%

62.2 Luminance

Sabino et al.,

(2020)

62.1 HG

53.2 HPAR

Black 50%

44.6 Luminance

42.4 HG

43.4 HPAR

Black 65%

26.6 Luminance

28.8 HG

27.8 HPAR

Black 80%

13.0 Luminance

14.3 HG

11.2 HPAR

Thermo-reflective

50%

27.1 Luminance

38.1 HG

35.4 HPAR

Red 50%

27.2 Luminance

45.9 HG

28.2 HPAR

Blue 50%

23.0 Luminance

34.0 HG

24.6 HPAR

Green 50%

27.9 Luminance

34.5 HG

27.4 HPAR

Borella et al.

Nativa, Sinop, v. 9, n. 5, p. 612-627, 2021.

625

According to Kotilainen et al. (2018), the spectral

composition (spectral quality) and fraction of reduced

irradiation are strongly affected by color, porosity, and

texture of shading screens. These authors found that black

screens (35%, 50%, 70%, and 80% shading) do not change

the quality of light in relation to the environmental solar light;

contrastingly, the spectral quality (UVB 280-315 nm;

GRAPE 315-400 nm; Blue 400-500 nm; Green 500-600 nm;

Red 600-700 nm; Far-red 700-800 nm; NIR 800-900 nm) is

affected by the color and porosity of shading screens.

The radiometric properties of plastic screens, combined

with different local weather conditions, season of the year,

and latitude, are responsible for transmission, reflection, and

absorption of solar radiation; these materials directly affect

the radiation balance inside protected microenvironments

and, consequently, modify the microclimate (ABDEL-

GHANY et al., 2015).

The transmitted solar radiation is retained and better used

for physical processes in the radiation balance, saving energy

(AHMED et al., 2016) and decreasing the irrigation water

consumption (MONTEIRO et al., 2016; BORELLA et al.,

2020a), benefiting the plant physiological performance

(ZHANG; ZHANG, 2017) and production quality

(KOTILAINEN et al., 2018).

Solar radiation affects other weather elements, mainly

temperature (Tar) and relative air humidity (URar). The use of

shading screens significantly decreases the sensitive heat in

subtropical climate (HOLCMAN; SENTELHAS, 2012) and

acts as a thermal insulation, decreasing heat loss in cold

regions, mainly during the night (AHMED et al., 2016). In

tropical climate regions under different water regimes,

shading results in a higher uniformity of Tar and URar values

for black and photoselective screens (BORELLA et al.,

2021).

In addition, the radiation retained by the shading screens

is reemitted as thermal radiation, generating a significant and

more homogeneous increasing in mean values of Tar and

URar under protected environments in tropical climate

regions, mainly when covered with photoselective screens

(BORELLA et al., 2021).

These dynamics of Tar and URar are due to convective

exchanges of energy for a lower volume of air inside these

shading environments, which contributes to a uniform

distribution of temperature and relative air humidity in the

vertical and horizontal extracts (AHMED et al., 2019) in

different regions (STATUTO et al., 2020) and seasons of the

year (BORELLA et al., 2021).

Considering these discussions, the appropriate choice of

shading materials for crop plants is dependent on their

characteristics regarding transmittance, spectral composition,

temperature and relative air humidity dynamics, and water

savings, associated with the ecophysiological requirements of

each plant species.

The angular coefficient of the regressions fitted for the

black screens decreased as the shading level was increased

(Figure 6); thus, the proportion of incident solar radiation

inside and outside the protected environment depends on the

shading level provided by the polyolefin screens. This was

not found for IPAR and luminance in the thermo-reflector,

red, blue, and green screens (Figure 7) because of the screen

color and, probably, the texture on the transmissivity of IPAR.

The coefficients of determination (R²) of the regressions

fitted for IG, IPAR, and luminance for the black and

photoselective screens showed that more than 80% of the

dependent variable (incident solar irradiance inside the

protected environment) is connected to the independent

variable (incident solar irradiance outside the protected

environment) (Figures 6 and 7). This is a good correlation,

despite 20% of the effect of external factors, as atmospheric

conditions (ZAMADEI et al., 2018) and radiometric

properties of plastic screens (ABDEL-GHANY et al., 2015).

These factors also induced under and overestimates of

deviations (MSE) and spreads (RMSE) of the measures.

However, they denote good performance of the equations,

with Willmott indexes (d) above 0.9973, which is satisfactory.

5. CONCLUSIONS

The diurnal and seasonal evolution of global irradiance

(IG), photosynthetically active irradiance (IPAR), and

luminance under shading screens follow the atmospheric

dynamics and are dependent on water seasonality and solar

declination of the region and on radiometric properties, such

as color and porosity of screens.

The transmission and absorption of IG, IPAR, and

luminance are affected by color and porosity, and the

reflection is affected by the shading screen color. The

arrangement and structure also affect the energetic properties

under these materials.

The simple linear regression statistical model is adequate

to estimate IG, IPAR, and luminance under protected

environments covered with black or photoselective shading

screens with different porosities when the irradiances are

measured under external environmental conditions.

The choice of shading screen for the planning and

developing of agricultural crops and forests depends on

information on the energetic needs of each species, the

spectral quality and transmissivity of photosynthetically

active radiation, and local external microclimate.

6. ACKNOWLEDGEMENTS

The authors thank the Brazilian Coordination for the

Improvement of Higher Education Personnel (CAPES;

Financing code 001); and the Brazilian National Council for

Scientific and Technological Development (CNPq) for the

scientific initiation and productivity scholarships (Process

308784/2019-7).

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