International Lighting in Controlled Environments Workshop
T.W.Tibbitts (editor) 1994 NASA-CP-95-3309 home | contents
LUMINAIRE LAYOUT: DESIGN AND IMPLEMENTATION (Short Report)
A.J. Both
The following information was presented during the discussion regarding guidelines for PAR uniformity in greenhouses. The data shows a lighting uniformity analysis in a research greenhouse for rose production at the Cornell University campus. The luminaire layout was designed using the computer program Lumen-Micro (Lighting Technologies, Inc., Boulder, CO). A total of 48 luminaires (General Electric, model GHL Low Profile, 400 Watt HPS) were installed (Figure 1). After implementation of the design, accurate measurements were taken in the greenhouse and the uniformity analysis for both the design and implementation were compared (Table 1). A study of several supplemental lighting installations resulted in the following recommendations:
> Include only the actual growing area in the lighting uniformity analysis (i.e., exclude any areas, such as walkways, at the edges of the growing area).
> For growing areas up to 20 m2: Take 4 measurements per m2, i.e., one measurement in the center of each 0.25 m2 (0.5 m by 0.5 m).
> For growing areas above 20 m2: Take 1 measurement per m2, i.e., one measurement in the center of each m2 (1 m by 1 m).
> Use one of the Uniformity Criteria (Table 2) and frequency graphs (Figure 2) to compare lighting uniformity amongst designs.
> Design for a Uniformity Criterion of at least 0.75 (preferably at least 0.90) and the fraction within ± 15% of the average PAR value should be close to 1 (Figure 2).
TABLE 1. Lighting uniformity analysis for the rose greenhouse at Cornell.
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Average Average ± 15% Min - Max Standard Deviation Growing Area (m2) Number of Data Points Number of Measurements m-2 Number of Luminaires Number of Luminaires m-2 Min/Avg Min/Max Uniformity Criterion 1 Uniformity Criterion 2 |
DESIGN 107 91-123 49-159 30 118 220 1.9 48 0.4 0.46 (≥0.80) 0.31 (≥0.70) 0.77 (≥0.75) 0.72 (≥0.75) |
IMPLEMENTATION 97 82-112 28-167 33 118 128 1.1 48 0.4 0.29 (≥0.80) 0.17 (≥0.70) 0.72 (≥0.75) 0.66 (≥0.75) |
TABLE 2 Definitions of two Uniformity Criteria (UC)
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UC 1 = 1 - [(S |Yi - Yave|)/(n * Yave)] |
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UC 2 = 1 - CV = 1 - [_ (S (Yi - Yave)2/(n - 1))]/Yave |
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where: Yi = PAR reading at location i |
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Yave = Average PAR reading over the growing area |
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n = Number of PAR readings over the growing area |
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CV = Coefficient of variation |
Fig. 1. Luminaire layout for a rose greenhouse at Cornell. Additional dimensions are: The bottom of the reflectors is located 1 m above the top of the canopy and the top of the canopy 1.95 m above the floor. The walkway along the left side wall is 1.45 m wide and the one along the right side wall 2 m. The distance between the luminaires in the top and bottom row is 1.22 m and the same distance in the center rows is 2.76 m. The distance between the top row and the top center row is equal to the distance between the bottom center row and the bottom row and is 1.8 m. The distance between the luminaires in the left and right columns is 2 m. The center luminaires of the left and right columns are positioned directly underneath the ridge of the greenhouse. The left most luminaire on the bottom row is positioned 2.5 m from the left side wall and also 2.5 m from the bottom side wall.
Fig. 2. Frequency graph for a rose greenhouse at Cornell.
REFERENCE
Albright, L.D. and A.J. Both (1994) Comparison of luminaires: efficacies and system design. Listed elsewhere in this publication.
Both, A.J. 1994. Luminaire layout: design and implementation, p 299-301. In: T.W.Tibbitts (ed.). International Lighting in Controlled Environments Workshop, NASA-CP-95-3309.
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