The Artificial Lighting Minefield (Part 2 Lighting Series)

Before the revival of Light-Emitting Diode (LED) technology, measuring and comparing lights for indoor cannabis cultivation was an easy and straight forward process. Like most of the horticultural industry, cultivators typically used High-Pressure Sodium (HPS) or Metal Halide (MH), and light intensity was measured by energy output generally for flowering, ranging from around 400 watts for modest set ups all the way up to 1000+ watts for the more serious cultivators. In those days of old, the increase in light intensity generally came at a cost of both higher energy consumption and elevating temperatures – two things best avoided – and if the budget allowed for it, the higher-output HPS lights were used with appropriate climatic control measures for maximum gains. The era could be looked upon almost nostalgically as a simpler time, especially as, since the emergence of LED cultivation lights, choosing the optimal light; type, manufacturer and settings has become an anxiety-inducing nightmare due to the overwhelming number of companies claiming to have the best lights in the world. Slightly tweaking the light spectrum, reducing energy consumption, reconfiguring layout and position, use of different housing material, on/off ramping, flexible racking, weight of units and more are all considerations that have become part of the headache of choosing the optimal lighting system. One could be forgiven for feeling overwhelmed.

As if to muddy the waters further, there is a lack of standardisation in how manufacturers gauge the productivity of their lights. PPF, PPFD, umol/m2-1/s-1, Lux, PAR, Watts, Lumens, Candela, and Footcandle are some of the terms found when trolling the net for a suitable light manufacturer (OK I put Footcandle in there for fun, but all others are real examples). Some of these units measure energy, some measure brightness, or flow of photons in set areas whilst others measure total flow. Having worked in a lab where the light intensity levels were crucial to the experiments, it is vital to have a standard universal method of measuring light intensity – especially with so many other variables involved in cultivation. This issue is further compounded by the fact that light spectrum plays a huge role in determining the output of plants.

As for the price comparison, HPS and MH lights are generally a good bit cheaper than LED – however, that statement is only true of the initial purchase since running costs of both are very different, with LED being the most favourable. In terms of outright purchasing cost, cultivation lights have a similar story to a cup of coffee from a café. In the mid 1990’s a cup of coffee in a UK café was usually somewhere between 20p – 50p, and the choice was one size, with sugar and/or milk – which you most likely added yourself.

Now the cost of a cup of coffee has spiralled beyond 10 times that, and the options available between cup size, milk type, coffee type, drink style, syrups and toppings etc would allow one to essentially try a different coffee drink each day for the best part of a year! This is every bit like the cultivation lights industry, where costs, choice and options have all spiralled to a point there’s possibly too much to choose from. Any meaningful comparison could only realistically compare 5-10 systems/different light manufacturers before controlling the other variables becomes unmanageable – not to mention space requirements and repetition numbers to validate the data. Therefore, it leaves a hole in the knowledge, adding more mystery to an industry already shrouded in misinformation and ‘bro-science’ and ultimately, an industry that lacks proper clarity at times.

In fact, proper comparisons between HPS and LED have also been sorely lacking in the peer-reviewed literature. There are still, from time to time, cultivators insisting on using HPS simply because it has proven effective in the past – but is this a good reason to continue? In a study set up to compare the different systems, Michel Jenkins and Curtis Livesay show some interesting data in their publication ’Photosynthetic Performance and Potency of Cannabis sativa L grown under LED and HPS Illumination’. In this study, which the authors claim to be a first of its kind, they start by comparing the consistency of light intensity within the area of coverage claimed by the manufacturers. Of the LED light systems tested, not only was there a larger variation than expected, but only one of the three manufacturers showed consistency close to what they claimed. The authors go on to show different metrics such as affect on leaf temperature and light response curves, but the most interesting claim was that LED light when averaged over 11 different cultivars produced ~5% more THCA than the equivalent grown under HPS. Showing that HPS produced an average of 20% THCA (+/- 3%) over the 11 cultivars and LED produced 25% (+/- 2.5%), the authors failed to provide further breakdown of the data. In addition, the study was straightforward and the selected experiments make sense, but there is some unsubstantiated claims in the introduction, and no access to the supplemental data where they break down the comparison of individual cultivars grown under both lighting systems. This data would help explain how cultivars react to the different lighting systems as a function of the genotype – it may reveal that some cultivars are more susceptible to the different lights versus others. However, showing the +/- reduction (range of results) using LED points towards higher consistency at least.

Conclusion

When considering a lighting system, it would be wise to consider the supplier, their reputation, and how their previous customers review and rate the system, as testimonials and third party validation are a useful proponent of the decision-making process. LED lighting for cultivation has become a minefield and it is so easy to get confused by all the options out there. Not understating the importance of competition in the market place to help drive prices down, make bespoke designs and keep driving innovation, but it would be so much handier if all these manufacturers used at least the same units of measurement and provided a comparison to a standard HPS. In addition, a standard ‘model’ cultivar would also increase reproducibility. This is a bit of a pipedream and unlikely to happen anytime soon, but as the industry continues to expand worldwide, cultivators and financers should surely be able to demand better standardisation and higher quality of researched data. It’s high time for an industry standard.