CHAPTER 1

SPECTRAL IRRADIANCE AVAILABLE FOR TURFGRASS GROWTH IN SUN

AND SHADE

ABSTRACT

The spectral quality of solarirradiance may affect plant growth and

development. Light energy reductions and spectral quality adjustments in

shaded environments have detrimental effects on both morphological and

physiological characteristics of turfgrass. Little research has addressed spectral

irradiance in shade for the past 30 years. The purpose of this study was to

assess the spectral quality of deciduous shade, coniferous shade, building

shade, and full sun in a natural turfgrass environment throughout the growing

season in Columbus, OH. A spectroradiometer was used to scan the solar

spectrum in these four light environments between 300 and 850 nm wavelength

in 5 nm increments on an hourly basis from 7:30 AM to 7:30 PM, bi-weekly, from

the vernal equinox to the autumnal equinox at The Ohio State University

Turfgrass Research Center. Scans were also made in the shade of industrial

shade cloth and compared to other shade environments. No significant

11

difference was found in photosynthetic light quality [(red light + blue light) I

green light] among coniferous, deciduous, and building shade or among tree

shades and shade cloth. Significant differences were detected among full sun,

tree shade, and building shade, for blue photoreceptor potential (far red light I

blue light) and for phytochrome potential (far red light I red light). Results

in~icated that the relationship of blue, red, and green light is not significantly

affected by shade but that receptor pigments affecting many plant processes

may be differentially affected by shade and full sun and by different shade types.

This study provides information concerning the quality of light in the shaded

environment that can be useful to turfgrass managers, but more importantly, to

turfgrass researchers in the pursuit of model systems for turfgrass health that

balance the use of trees and turfgrass in the landscape.

12

INTRODUCTION

Solar irradiance available for turfgrass growth occurs in a spectral band

from 400 to 700 nm wavelength and is referred to as photosynthetically active

radiation (PAR)(Figure 1.1). Plant pigments, including chlorophylls and

carotenoids, absorb light at specific wavelengths. Chlorophyll a has peak

spectral absorption at approximately 410, 430, and 660 nm (French 1961).

Chlorophyll b absorbs most effectively at 430, 455, and 640 nm and carotenoids,.

including xanthophylls, absorb best at approximately 450 nm. Phytochrome, a

pigment implicated in cell elongation, chloroplast development, and carotenoid

biosynthesis (Harding and Shropshire 1980) absorbs wavelengths preferentially

near 730 nm (Grant 1997). Using these findings, PAR can be divided into active

and inactive wavelengths based on pigment absorption bands. PAR from 400 to

500 nm, referred to as blue light (B), and PAR from 600 to 700 nm referred to as

red light (R), is active for photosynthesis, photomorphogenesis, and chlorophyll

synthesis (Blackwell 1966). PAR from 500 to 600 nm, referred to as green light

(G), is basically inactive for plant growth and development.

13

Shade, regardless of the shade source, reduces PAR and affects plant

photosynthesis (Figure 1.1). Low light intensities and other components of the

shaded environment such as tree root competition and restricted air movement .

result in morphological and physiological conditions detrimental to turfgrass

growth (Dudeck and Peacock 1992). The severity of these conditions may be

affected by low levels of irradiance, by spectral quality of irradiance, or both.

Light quality, the proportions of spectra included in available irradiance,

may have significant effects on turfgrass health. McBee (1969) reported that

growth of bermudagrass (Cynodon dacty/on L.) improved when B was present

and R was filtered compared to R present and B filtered. McKee (1963) used a

color temperature meter to characterize light quality in the shade of buildings,

the shade of tree canopies, and the shade of herbaceous plants. Blue light in

comparison to red light was enriched in the shade of a deciduous tree canopy

and in the shade of a building, but declined in the shade of conifers and in

herbaceous shade. Gaskin (1965), using a similar instrument, found no

difference between light quality under green saran shade cloth and light quality

in tree shade providing the shade cloth used resulted in light reductions between

25 and 75%) full sun. Yet, it was suggested that building shade filtered less blue

light than oak (Quercus sp.) and maple (Acer sp.). Vezina et at. (1966)

demonstrated a reduction in red and blue wavelengths and a proportionate

increase in green and far red wavelengths under a deciduous forest canopy but

14

found a neutral shade with respect to light quality under a coniferous forest

canopy. The results of.these studies appear contradictory in some cases.

Many research projects attempt to study the effects of shade using

industrial shade cloth to create light reductions. Shade cloth of neutral color

does not affect light quality in relation to full sun (McMahon et al. 1990) and may

no! differ considerably from the shade of trees (Gaskin 1965). Little research has

been done concerning light quality in shade since the 1960's and much of this

research was done using light temperature meters which only assess quantities

of blue and red light. More recent research has focused on assessing light

quality within tree canopies (Grant et al. 1996; Gilbert et al. 1995) or within

forests (Turnball and Yates 1993; Baldocchi et al. 1984). Because of the

influence of diffuse light, which may strike the earth's surface at almost any

angle infiltrating the shade created by a single tree or small group of trees, and

because of reflection occurring within a tree canopy, assessment of light quality

within tree canopies is not consistent with light quality beneath the canopy. Few

plants are adapted for growth in forests and the absence of diffuse light in forest

environments is not consistent with light quality in shaded situations where

horticultural plants are grown. Sophisticated equipment is now available for the

measurement of light spectra and may provide more definitive results than those

previously demonstrated. In addition, recent research has implicated

relationships between phytochrome and an unknown blue light receptor, often

15

called cryptochrome, which affect many plant processes. The purpose of this

study was to assess the spectral quality of deciduous shade, coniferous shade,

building shade, and full sun in a natural environment common to turfgrass

growth throughout the growing season in Columbus, OH.

16

MATERIALS AND METHODS

Spectral irradiance data were collected using a model LI-1800

spectroradiometer (LiCor, Lincoln, NE) hourly from 7:30 AM to 7:30 PM,

bi-weekly, from the vernal equinox to the autumnal equinox in 1997. Scans were

made at The Ohio State University Turfgrass Research Center beginning April

11, 1997 and ending September 10, 1997. Deciduous trees were in full leaf

beginning with scans made on June 6, 1997 and comparisons among

deciduous, coniferous, and building shade were made after that date. Data

collected beginning April 11, 1997 were used for comparisons not involving

deciduous shade.

Scans were made in the shade of a single tree or building and in full sun

at the same location each time and in the same order each hour. Scans were

made so that direct solar irradiance was measured after passing through

approximately the same portion of the canopy each time. The distance from the

trunk of the tree where scans were made varied with the height of the sun in the

sky at the time of scanning. During solar noon, scans were made very close to

the trunk of the tree providing shade. At this time, direct radiation was required

17

to pass through a large portion of the tree canopy before reaching the detector.

In the early morning or late afternoon, scans were made much farther from the

tree and the canopy density filtering direct solar radiation was somewhat

reduced because of sun angle. The trees used were a Norway spruce (Picea

abies), approximately eight meters tall, and a black walnut (Jug/ans nigra L.),

approximately 10m tall. Sunny or cloudy weather was considered a random

occurrence and a part of the natural environment and scans were made

regardless of cloud conditions. Scans were not made during periods of rain

because moisture could affect the accuracy of the sensing mechanism.

Scans were also made in the shade of black industrial shade cloth

(Chicopee, Gainesville, GA) resting on structures constructed of polyvinyl

chloride pipe at the Turfgrass Research Center. Two of these structures were

vertical and covered with shade cloths rated for 80% light reduction or 100%

light reduction. A third structure was covered on top and on two sides with shade

cloth rated at 80% light reduction. Each of these structures were replicated three

times. Scans were made twice, morning (AM) and afternoon (PM), on July 15,

July 29, and August 26, and once on June 5 (PM), and July 2 (AM) for a total of

eight replications. Data from these scans were averaged over the three

structural treatments and compared to scans of deciduous shade, coniferous

shade, and the shade of a partial red brick and partial white aluminum building

under variable skies.

18

Data for all scans were collected for total photosynthetic photon flux

density (PPFD) and for radiant energy from 300 to 850 nm wavelenght in 5 nm

increments. Photon flux density (PFD) was calculated for 8 from 400 to 500 nm,

for G from 500 to 620 nm, and for R from 620 to 680 nm. These spectral ranges

identified active (R + 8) and inactive (G) light based on spectral absorption of

plant pigments (Figure 1.2). Peak absorption of phytochrome occurs at

approximately 730 nm so a range from 710 to 750 nm was used to evaluate FR.

Analyses of variance were performed to compare photosynthetic potential [(8 +

R) I G], blue photoreceptor potential (FRl8), and phytochrome potential (FRlR)

in deciduous, coniferous, and building shade. Time of day and month were used

as blocking criteria to limit variation due to daily and seasonal changes in

spectral intensity and quality. Mean light responses were separated using least

significant difference. Significance was tested at the P < 0.05 level for all

analyses.

19

RESULTS AND DISCUSSION

Changes in PPFD occurred parabollically throughout each day (Figure

1.3). Irradiance increases slightly after solar noon. Conversely, this study

demonstrated a nonsignificant decline in irradiance after solar noon probably

due to increasing cloud cover. The average PPFD for 2,3, and 4 h before solar

noon throughout the study was 23,710,861 urnol S-1 rn? and for 2, 3, and 4 h

after solar noon was 18,983,792 urnol S-1 m-2 . Continental climates, such as that

in Columbus, OH, tend to have more cloud cover in the afternoon compared to

cloud cover in the morning during the growing season. Cloud cover scatters light

and may affect light quality (Salisbury and Ross 1992). Over the season and in

full sun, B compared to PPFD was significantly less in the morning (0.197) than

in the afternoon (0.205); G was basically the same (AM = 0.538; PM = 0.539); R

proportion was significantly greater in the morning (AM = 0.266; PM = 0.255);

and FR proportion did not change (AM = 0.120; PM = 0.118). (B+R)/G and FRIR

were unaffected by time of day but FRIB decreased significantly in the afternoon

compared to the morning. This decrease in FRIB is consistent with results

predicted for cloud cover. Under cloud cover, B irradiance was proportionately

20

higher than under clear sky due to increased diffusion and cloud reflection and

FR was proportionately lower due to absorption of FR by water vapor. Because

cloud cover did not significantly effect FRIR levels and because B during

daylight is in a saturating condition for blue photoreceptors, these differences

between light quality in the morning and in the afternoon were not considered to

have major impacts on plant development. Persistent periods of cloud cover,

however, may affect photosynthetic production if light levels fall below light

compensation points for desirable plant species (Figure 1.3).

During the course of the study, PPFD in deciduous shade averaged 61%

of PPFD in full sun, coniferous shade was 16% of full sun, and building shade

was 23% of full sun. PPFD under vertical shade structures covered with 80%

shade cloth averaged 35% of PPFD in full sun. Under vertical shade structures

covered with 100% shade cloth the average PPFD was 27% of full sun and

under structures covered on top and two sides with 80% shade cloth, the

average was 20% of full sun. (B+R)/G and FRIB did not vary among deciduous,

coniferous, building, and shade cloth treatments but FRIR showed significant

variation (Table 1.1). There was no variation in PAR among deciduous shade,

coniferous shade, and shade cloth supporting Gaskin (1965) but variation was

detected between coniferous shade and shade cloth for levels of FRIR not

considered by that study. Because of this variation, shade cloth did not

accurately mimic tree canopy shade. Increases in phytochrome r which are likely

21

to occur in coniferous shade may not occur in the shade of industrial shade

cloth. The results for this test did not indicate the variation expressed in the

season-long study among full sun, deciduous shade, coniferous shade, and

building shade (Table 1.2) possibly because replication was not sufficient to

reduce experimental error.

Scans made from June through September at the Turfgrass Research

Center indicated that (B+R)/G did not vary among deciduous shade, coniferous

shade, building shade, and full sun, but FRIB and FRIR varied significantly

(Table 1.2). These results suggest that all shade treatments created a spectral

environment conducive to photosynthesis. Photosynthesis, however, may be

affected directly (Eskins et al. 1991) or indirectly by the relationship between

blue light photoreceptors and phytochrome in shade. Graphic analysis of

deciduous, coniferous, and building shade (Figure 1.4) suggested variation

between light quality in these shade environments compared to full sun. In each

shade type, the proportion of B increased compared to full sun, the proportion of

G remained the same, R proportion declined, and FR increased.

Full sun contained significantly higher FRIB and significantly lower FRIR

than any of the shade treatments. FR/B was significantly higher in full sun than

in coniferous or deciduous shade and these tree shades contained significantly

higher FR/B than building shade. FR increased in intensity in relation to R in the

shade of a plant canopy compared to the shade of a building and to full sun and

22

all shade treatments contained higher levels of FRIR than full sun (Table 1.2).

Recent research has demonstrated that starch and sucrose synthesis and

degradation (Doelgeret al. 1997; Dewdney et al. 1993), nitrate uptake,

reduction, and utilization (Teller at al. 1996; Kamiya 1995; Lopez-Figueroa and

Ruediger 1991), stem and hypocotyl elongation (Ahmad and Cashmore 1997;

Casal and Sanchez 1994; McMahon et al. 1991), leaf area expansion (Eskins

1992; Van Volkenburgh et al. 1990), and cell division (Furuya et al. 1997;

Zandomeni and Schopfer 1993; Muenzner and Voigt 1992) are affected by the

proportions of 8, Rand FR in the light environment, but these relationships have

not been fully elucidated. An antaqontstic relationship is believed to exist

between blue photoreceptors and phytochrome, often dominated by the blue

photoreceptors. The extent of that domination is currently unknown but the

results of this study demonstrated that reasonable evidence exists to indicate

differential plant metabolism in shade compared to full sun and in building shade

compared to tree shade.

Light quality did not vary among deciduous, coniferous, and building

shade with respect to photosynthetically active radiation. Photosynthetically

active radiation did not differ significantly in spectral quality between industrial

shade cloth and normal shade environments but may vary in FR content. The

proportion of FR/B varied among full sun, coniferous and deciduous shade, and

23

building shade. Proportions of FRIR were highest in the shade of a plant

compared to the shade of a structure.

This study provides information concerning the quality of light in the

shaded environment that can be useful to turfgrass managers, but more

importantly, to turfgrass researchers in the pursuit of model systems for turfgrass

health that balance the use of trees and turfgrass in the landscape.

24

REFERENCES

Ahmad, M., and A.M. Cashmore. 1997. The blue-light receptor cryptochrome 1shows functional dependence on phytochrome A or phytochrome B inArabidopsis thaliana. Plant J. 11(3):421-427.

Baldocchi, D.D., B.A. Hutchinson, D.R. Matt, and R.T. McMillen. 1984. Solarradiation in an oak-hickory forest: an evaluation of extinction coefficients forseveral radiation components during full-leafed and leafless periods. Agric.Forest meteorol, 32:37-322.

Bell, G.E. 1997. Temporal Shade on Creeping Bentgrass Turf. Dissertation. TheOhio State University, Columbus, OH.

Blackwell, M.J. 1966. Radiation meteorology in relation to field work. In: R.Bainbridge, G.C. Evans, and O. Rackharn (ed.) Light as an Ecological Factor.Wiley, New York, NY.

Casal, J.J. and R.A. Sanchez. 1994. Impaired stem-growth responses toblue-light irradiance in light-grown transgenic tobacco seedlings overexpressingAvena phytochrome A. Physiologia Plantarum 91(2):268-272.

Dewdney, J., T.R. Conley, M.C. Shih, and H.M. Goodman. 1993. Effects of blueand red light on expression of nuclear genes encoding chloroplastglyceraldehyde~3-phosphate dehydrogenase of Arabidopsis thaliana. PlantPhysiol. (Rockville) 103(4):1115-1121.

Doelger, K., U.K. Tirlapur, and K.J. Appenroth. 1997. Phytochrome-regulatedstarch degradation in germinating turions of Spirode/a po/yrrhiza.

Dudeck, A.E. and C.H. Peacock 1992. Shade and turfgrass culture. In: D.V.Waddington, R.N. Carrow, and R.C. Shearman (ed.) Turfgrass. AmericanSociety of Agronomy, Madison, WI.

25

Eskins, K. c.z. Jiang, and R. Shibles. 1991. Light-quality and irradiance effectson pigments light-harvesting proteins and rubisco activity in achlorophyll-harvesting-deficient and light-harvesting-deficient soybean mutant.Physiologia Plantarum 83( 1).47 -53.

Eskins, K. Light-quality effects on arabidopsis development red blue and far-redregulation of flowering and morphology. Physiologia Plantarum 86(3):439-444.

French, C.S. 1961. Light pigments and photosynthesis. In: W.D. McElroy and B.Blass (ed.) A Symposium on Light and Life. John Hopkins Press, Baltimore, MA.

Furuya, M., M. Kanno, H. Okamoto, S. Fukuda, and M. Wada. 1997. Control ofmitosis by phytochrome and a blue-light receptor in fern spores. Plant Physiol.(Rockville) 113(3):677-683.

Gaskin, T.A. 1965. Light quality under saran shade cloth. Agron. J.57(3):313-314.

Grant, T.H. 1997. Partitioning biologically active radiation in plant canopies. Int.J. Biometeorol. 40:26-40.

Grant, R.H., G.M. Heisler, and W. Gao. 1996. Photosynthetically-activeradiation: sky radiance distributions under clear and overcast conditions. Agric.Forest Meteorol. 82(1-4):267-292.

Harding, R.W. and W. Shropshire, Jr. 1980. Photocontrol of carotenoidbiosynthesis. Ann. Rev. Plant Physiol. 31 :217-238.

Kamiya, A. 1995. Effects of blue light on the uptake of ammonia and nitrate by acolorless mutant of chlorella. Plant & Cell Physiol. 36(3):481-485.

Lopez-Figueroa, F., and W. Ruediger. 1991. Stimulation of nitrate net uptakeand reduction by red and blue light and reversion by far-red light in the greenalga Ulva rigida. J. Phycology 27(3):389-394.

McBee, G.G. 1969. Association of certain variations in light quality with theperformance of selected turfgrasses. Crop Sci. 9: 14-17.

McKee, G.W. 1963. Use of a color temperature meter to characterize lightquality in the field. Crop Sci. 3:271-272.

26

McMahon, M.J., J.W. Kelly, and D.R. Decoteau. 1990. Spectral Transmittance ofSelected Greenhouse Construction and Nursery Shading Materia/. J. Environ.Hort.8(3):118-121.

McMahon, M.J., J.W. Kelly, D.R. Decoteau, R.E. Young, and R.K. Pollock. 1991.Growth of Dendranthema grandiflorum Ramat. Kitamura under various spectralfilters. J. Am. Soc. Hort. Sci. 116(6):950-954.

Muenzner, P. and J. Voigt. 1992. Blue light regulation of cell division inChlamydomonas reinhardtii. Plant Physio/. (Bethesda) 99(4): 1370-1375.

Salisbury, F.B. and C.W. Ross. 1992. Plant Physiology (4th ed.). WadsworthPublishing, Belmont, CA.

Teller, S., K.H. Schmidt, and K.J. Appenroth. 1996. Ferredoxin-dependent butnot NADH-dependent glutamate synthase is regulated by phytochrome andablue/UV-A light receptor in turions of Spirodela polyrhiza. Plant Physio/.Biochem. (Paris) 34(5):713-719.

Turnball, M. H. and D.J. Yates. 1993. Seasonal variation in the red/far-red ratioand photon flux density in an Australian sub-tropical rainforest. Agric. ForestMeteoro/. 64: 111-127.

Van Volkenburgh, E., R.E. Cleland, and M. Watanabe. 1990. Light-stimulatedcell expansion in bean Phasiolus bulgaris L. leaves II. Quantity and quality oflight required. Planta (Heidelberg) 182(1 ):77 -80.

Vezina, P.E. and D.W.K. Boulter. 1966. The spectral composition of nearultraviolet and visible radiation beneath forest canopies. Can. J. Bot.44: 1267 -1283.

Zandomeni, K. and P. Schopfer. 1993. Reorientation of microtubules at the outerepidermal wall of maize coleoptiles by phytochrome blue-light photoreceptor andauxin. Protoplasma 173(3-4): 103-112.

27

(B+R)/G FRIB FRIR

Treatment Mean Treatment Mean Treatment Mean

Building 0.8801 a Full Sun 0.5778 a Coniferous 0.5595 a

Coniferous 0.8724 a Deciduous 0.5545 a Deciduous 0.5165 ab

Deciduous 0.8708 a Coniferous 0.5331 a Building 0.4764 b

Cloth 0.8603 a Cloth 0.4993 a Cloth 0.4606 b

Full Sun 0.8521 a Building 0.4478 a Full Sun 0.4479 b

p= 0.08 P = 0.19 LSD= 0.69

Table 1.1. Means of active in relation to inactive light [(B+R)/G], blue lightreceptor potential (FRlB), and phytochrome potential (FRlR) forspectroradiometric scans made on June 5 (PM), July 2 (AM), July 15 (AM andPM), July 29 (AM and PM), and August 26 (AM and PM) in Columbus, OH.Scans were made in the shade of industrial shade cloth, coniferous shade,deciduous shade, building shade and full sun. Letters following treatment meansindicate significance (P = 0.05). B refers to photon flux density (PFD) between400 and 500 nm wavelength. G is PFD between 500 and 620 nm and R is PFDbetween 620 and 680 nm. FR represents PFD between 710 and 750 nm.

28

(B+R)/G FRIB FRIR

Treatment Mean Treatment Mean Treatment Mean

Coniferous 0.9067 a Full Sun 0.5984 a Coniferous 0.5392 a

Building 0.8707 a Coniferous 0.5691 b Deciduous 0.4926 b

Deciduous 0.8654 a Deciduous 0.5651 b Building 0.4725 c

Full Sun 0.8654 a Building 0.5111 c Full Sun 0.4538 d

P = 0.39 LSD= 0.02 LSD = 0.01

Table 1.2. Means of active in relation to inactive light [(B+R)/G], blue lightreceptor potential (FRlB), and phytochrome potential (FRlR) forspectroradiometric scans made hourly from 7:30 AM to 7:30 PM on a bi-weeklybasis in Columbus, OH from the vernal equinox to the autumnal equinox. Scanswere made in coniferous shade, deciduous shade, building shade and full suneach hour. Letters following treatment means indicate significance (P = 0.05). Brefers to photon flux density (PFD) between 400 and 500 nm wavelengths. G isPFD between 500 and 620 nm and R is PFD between 620 and 680 nm. FRrepresents PFD between 710 and 750 nm.

29

60,000 ,-------------------------,

~~ 30,000C1)ewC 20,000

C'CS=c~ 10,000

O~~~~~~~~~~~~~~~~~~~~~~~300 350 400 450 500 550 600 650 700 750 800 850

Wavelength (nm)

-E. 50,000crfA.•••.3: 40,000-

D Full Sun • BuildingShade

Figure 1.1. Solar radiant energy graphed according to wavelength in full sun andin building shade on a clear day. The white area displays photon flux density infull sun. The black area displays photon flux density in the shade of a buildingand is graphed over levels of full sun for visual comparison. Notice the severerestriction of irradiance available in building shade compared to full sun.

30

1.5

0.5

o~~~~~=-~~~~~~~~~~~~~~~~~--~~375 400 425 450 475 500 525 550 575 600 625 650 675 700 725 750

Wavelength (nm)

Figure 1.2. Spectral composition of plant pigments in creeping bentgrass(Agrostis palustris Huds.) leaf tissue extracted in 80% (v/v) acetone. Thespectrum was identified in 1 nm increments using a Cary 3E spectrophotometer.Peak absorption of pigments may vary depending on the solvent used forextraction.

31

40~------------------------------------------------~

" .... Building Shade• ,'_ •• ~ ~••••••• ,-." •• ,- ••••••• ~••.• ,- " •••••••• ,,-~- •• -- •••• "'" •• ", -0,....,.- .

..•...•.

..•...•.

..•. ,

Full Sun"'----- ..••.

-30a-enE

,"""

,,

""

,,-(.)cu~ 20

IcLLa.a. 10

""

,,•...

"" Deciduous Shade •...•... ,"" •...

"II

I

""

o~--~--~--~--~--~----~--~--~--~--~--~--~07:30 08:30 09:30 10:30 11:30 12:30 13:30 14:30 15:30 16:30 17:30 18:30 19:30

Hour

Figure 1.3. Photosynthetic photon flux density (PPFD) under variable skies inColumbus, OH. Measurements in full sun, deciduous shade, coniterous shade,and building shade are displayed hourly from 7:30 AM to 7:30 PM. Hourly resultsare averaged over 12 spectral scans made biweekly from vernal equinox toautumnal equinox.

32

Deciduous Coniferous Building

••••••••••••••••••• _~~~~ .~~~~~_ Shade

§ -.."..-..-.._..-..-..- _ _.._..-.._ _ _ -.._.._ -..-..UJ

:;LL-Q)"C<Us:

UJ -----.- ........•- --.-.-.-.- ----- ~.-.~.-.-.--.__ -.350 400 450 500 550 600 650

Wavelength (nm)

700 750 800 850

Figure 1.4. Solar irradiance in deciduous, coniferous, and building shadedisplayed by wavelength and as a proportion of irradiance in full sun. Radiantenergy at each wavelength in shade was divided by radiant energy in full sun. Ahorizontal line would indicate no change in light quality between sun and shade.Irradiance was averaged over 146 spectral scans made hourly from 7:30 AM to7:30 PM, bi-weekly, from vernal equinox to autumnal equinox in Columbus, OH.

33