Vergara - 1976 - Physiological and morphological adaptability of ri

146 CLlxL-Yfl-L AND RILTE
DUPLICATION OF NATURAL CONDITIONS
Lighting
The relevance of these heat-exchange physics to the two types of lighting and
their cost implications depends completely on whether the light from the artificial
sources can essentially simulate that received nattirally
From the physical standpoint the artificial source must provide: (l) a spcetium
equivalent to daylight. (Z) an intensity" range equivalent to daylight. (3) an
even. diffuse light over the plant-growing area.
Providing these requirements introduces a very complex subject. First, no one
artificial light source, or any presently known combination of sources at reasonable
cost, can completely simulate a standard daylight spectrum within the
physiologically’ active range of radiation. Second. the important physiological
characteristics of natural radiation conditions and of “normal" plant growth
under external conditions are difficult to define with certainty The more this
is examined in detail, to set operating standards, the more elusive absolute
definitions become
As to radiation. there are variations in the spectral balance according to solar
angle and hence by season. latitude and time of day’ (Fig. l). Some of these
variations become quite substantial, and they fluctuate because of presence or
Spectral imam-ea (w-nrznmh
4.0
20
O6
O4
O2
O I .
300 500 700 900 tl0O
Wavelength l nrn}
l. Spectral lITEldiZlHCB distribution curves for sunlight
xvitlt m » 0. l. 2. 3. 4. S (adapted from Fig. l0. Niloon.
1940)‘