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Composite Lighting for Controlled-Environment
Plant Factories
Joel L. Cuello
The University of Arizona, Tucson, Arizona
915I. INTRODUCTION
One of the consequences of employing artificial lighting to supplement solar irradiance either in a green-
house [1–3] or in a controlled-environment plant growth chamber, wherein solar irradiance is transmitted
through optical cables from solar concentrating systems [4–6], is the subjection of the growing crops to
lighting profiles that differ from the conventional lighting profile. The daily lighting profile of a conven-
tional electric-based plant-lighting system can generally be represented by a rectangular wave (Figure
1A) whose height represents the magnitude of the instantaneous photosynthetic photon flux (PPF, in
mol m^2 sec^1 ), whose length represents the daily photoperiod (P, in hr), and whose area represents the
daily integrated PPF (Q, in mol m^2 day^1 ). For a hybrid solar and artificial lighting system, the daily
lighting profile that results is a composite lighting profile (Figure 1B), typically consisting of an approx-
imately bell-shaped curve, representing the solar component, that is superimposed over a rectangular
wave, representing the artificial lighting component. The total of the area under the solar curve and the
area of the rectangular wave represents the daily integrated PPF.
This chapter would show that composite lighting could significantly influence the physiological re-
sponses of crops, particularly photosynthesis and respiration, and thus could be harnessed as a practical
strategy for improving crop growth and productivity. The adoption of composite lighting for controlled-
environment crop production rests on the principal premise that, depending on the lighting profile em-
ployed, equal moles of photons delivered to two crop treatments do not necessarily result in equal growths
for the two treatments.
II. FEATURES, TYPES, AND PARAMETERS
A. Features of Composite Lighting
Composite lighting is a lighting profile that possesses the following essential features:
- Two significantly distinct instantaneous PPF levels (one high and one low), each applied with
its own photoperiod (Figure 2A). It should be noted that a solar component’s nonrectangular
curve could be represented by an equivalent rectangular wave whose area is equal to that of the
original curve and whose height is the average instantaneous PPF in the original curve.