Horticultural lighting design and Déjà Vu

Before the 1980s, architectural lighting design was more art than science. Electrical engineers needed nothing more than pencil and paper to perform lighting calculations by hand. This all changed, of course, with the introduction of personal computers. Today’s architectural lighting design software began with simple programs that had a particular problem. Luminaire manufacturers published plots and tables of photometric data for lighting designers, but these were useless for computer calculations.

The Illuminating Engineering Society recognized this problem, and in 1981 introduced a standardized computer file format for representing photometric data (ANSI/IES 2019). Unfortunately, the initial response of the major luminaire manufacturers was to simply ignore this development. The argument at the time seemed reasonable enough: the published plots and tables were included in printed catalogs that sales representatives could hand-deliver to their clients. These visits generated sales opportunities that would be lost if lighting designers were able to do computer-aided calculations themselves.

Following this argument, the luminaire manufacturers mostly decided that their product data was proprietary and that clients would be better served by requesting custom light plans through their sales representatives, in a word (or two), déjà vu. Four decades later, this is precisely the argument that most horticultural lighting manufacturers are offering.

With this as historical background, it is interesting to look at the current state of horticultural lighting design. At present, not a single horticultural luminaire manufacturer offers publicly available photosynthetic photon intensity distribution (PPID) or spectral quantum distribution (SQD) information for their products. When asked, the explanation is familiar: the information is proprietary, but custom light plan services are available for qualified clients.

It has been argued that the horticultural lighting industry does not need any more detailed information than this. While architectural lighting design programs such as Lighting Analysts’ AGi32 and DIAL’s DIALux are capable of performing basic horticultural lighting calculations, few people in the horticultural industry are interested in investing the time and effort needed to master these programs. It makes much more sense for clients to simply request custom light plans from the luminaire manufacturers.

One of the tragedies of today’s horticultural lighting industry is that it is, for the most part, years behind academic research in terms of plant responses to the light source spectrum from 280 nm (ultraviolet-B) to 800 nm (far-red). As but one example, most luminaire manufacturers until recently offered products with only red and blue LEDs, arguing that their 450 nm (blue) and 660 nm (red) spectral outputs matched that of the spectral absorptance peaks of chlorophyll A/B and so maximized photosynthesis.

Read the complete article at www.allthingslighting.com.

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