Design Tools for Horticultural Lighting

ABSTRACT

Horticultural lighting poses unique problems for professional lighting designers. Simply put, today’s lighting design software is ill-suited to the task of designing lighting systems for greenhouses and vertical farms.

One problem is that existing photometric data formats are based on photopic lumens and human observers. Plants respond to the spectral power distributions (SPDs) of light sources very differently, and so require photon-based metrics such as Photosynthetically Active Radiation (PAR). More generally, the light source SPDs must also be available for design purposes. These issues are being addressed by new ANSI industry standards being developed by the American Society of Agricultural and Biological Engineers and the Illuminating Engineering Society.

Another problem is that greenhouses may require both supplemental electric lighting and automated shades to meet the Daily Light Integral (DLI) requirements of various crops. For design purposes, this requires historical weather data for climate-based annual daylighting design, as well as consideration of the optical properties of greenhouse glazing and covering materials. Efficient algorithms to perform the necessary daylighting calculations, including bidirectional transmittance distribution functions (BTDFs) for diffusing materials, have only recently been developed.

For vertical farms (plant factories), it is important to model the distribution of spectral irradiance at the plant canopy, with a spectral range of 280 nm to 800 nm. Research has shown that while red and blue visible light is sufficient for photosynthesis, ultraviolet light is needed for insect and fungal control, while green light and far-red radiation (700 nm to 800 nm) is important for photomorphogenesis. It is therefore necessary to model the full SPD of light in the horticultural environment, not just the red, green, and blue light considered by today’s lighting design software.

Finally, intracanopy lighting design may require modeling three-dimensional light distributions within the crop rather than just at the crop canopy.

LEARNING OBJECTIVES

1. Explore the opportunities for professional lighting designers in horticultural lighting.
2. Understand the connection between climate-based daylighting and greenhouse lighting design.
3. Learn how and why plants perceive light and color differently from humans.

SPEAKER

Ian Ashdown, P. Eng., FIES
Senior Scientist, SunTracker Technologies Ltd.

Ian Ashdown is Senior Scientist for SunTracker Technologies Ltd. and Lighting Analysts Inc. He holds over 140 patents and patent applications related to lighting design and research, and is responsible for the photometric calculation and architectural visualization engines of Lighting Analysts’ AGi32, ElumTools, and Licaso lighting design software products. He is currently developing lighting design software tools expressly for greenhouses and vertical farms.

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