Vergara - 1976 - Physiological and morphological adaptability of ri

PHYSICS or cosmoumo ENVIRONINIENT AND PLANT esowm 147
absence of cloudy weather or atmospheric contaminants. Plants also vary immensely
according to the conditions they are grown in outside.
As we penetrate this jitngle of complexity we come to a conclusion tvhich
we believe will be inereasinglyt shared by others: artificial light sources can
provide light with intensities and spectral qualities that effectively simulate the
natural radiation received during the main light hours of the day‘. eg. a spectrum
with air mass = 2 (Moon, 1940). The confirmation comes from comparing
the morphological and biochemical characteristics of plants grown under these
conditions with those grown under outside or naturally lit conditions. In our
experience it has been found that what were initially thought to be defects of
artificially‘ lit plants were, in fact. typically characteristic responses of plants
to equivalent combinations of temperature. humidity-i. and light conditions
when grown outside.
Once it is accepted that artificial light can adequately duplicate natural light,
we can then unravel the complexities of important physiological interactions of
spectral changes of natural light during the day and between seasons as these
affect efficiencies and the course of development of plants. In saying this. we are
very conscious of the subtietles of many of these interactions between light
environment and the course of plant development. Accepting this principle.
that artificial light can duplicate natural light, one must continuously watch for
situations in which new features need to be built into the artificial lighting
systems so that they do replicate particular sets of extemal-light environment
regimes. This in itself is typical of the fascination, the challenge. and the sense
of trpportunity’ in all aspects of controlled-environment work.
Spectral balance and lamp tgrpes
Table 2A presents results from a comparison of different types of high-pressure
vapor-discharge lamps which were tested at the Climate Laboratory. Each main
Table 2.
A. Plant responses to different light sources.
Lamp type
HPLR-based HPl-based Metalarc~based LSD 0.05
Soybean
RGR (g ~g-' day-'-) 0.130 0.131 0.132 0.008
Stem lenglhtcm) 18.3 18.5 20.8 2.4
Leat carbohydrate (%) 20.5 15.4 201 2,6
Protein (%) 26.5 28.6 25.9 1.4
B. Plant responses to spectral imbalance
Spectral treatment
Blue-biased Balanced Red-biased LSD 0.05
Sorghum
Shoot d- Wt- (9) 11.52 20.11 2115 3,31
Stem length (cm) 58.9 84.1 1115 650
Leaf carbohydrate (%) 71 3] g_g 1_3
Leaf protein (%) 26.7 23.2 191 11
A. From Warrington and Mitchell (1915)
B. From Warrington and Mitchell (1976)