Grow Lighting: LED vs. HPS

With America quickly noticing how much power the cannabis industry draws from the grid (as high as one percent of the country’s total electricity usage), the hunt is on for the most efficient grow light. It’s well known that more expensive LED lights are much cheaper than others, but does this really apply to growing plants? Is it really worth making the switch from HID to LED?

A study published this June concluded that “the most efficient HPS and LED fixtures have equal efficiencies, but the initial capital cost per photon delivered from LED fixtures is five to ten times higher than HPS fixtures.” Yes that’s right, they measured light by the photon; pretty intense right?

Another interesting finding in the study is that light quality is much less important than light quantity. While light quality will govern certain aspects of plant metabolism, it has a small effect on photosynthesis, which is the most important driving factor in plant development. While this goes against what many LED grow light manufacturers have to say about their products and the wavelengths they put out but, the fact remains that HPS lights are still the workhorse of the indoor cannabis industry, and for good reason.

It wasn’t just any kind of HPS light that took the crown in that study: double-ended HPS fixtures were around 60% more efficient than the common mogul-base HPS fixtures.

The study suggests that “just as precision irrigation can improve water efficiency, precision lighting can improve electrical efficiency,” meaning that different arrangements in a grow room or greenhouse would require HPS, LED, or both in tandem. Grow rooms with highly spaced benches will benefit from LED lighting because it provides a more focused beam. On the other hand, grow rooms with more of a “sea of green” would benefit from HPS because less light would be lost to the floor or walls in its wider beam. LED’s have the advantage of being cooler to the touch and they can be used right in between the plants where 100% of light emitted gets captured. The precision delivery of light in LED fixtures also makes them ideal for supplemental greenhouse lighting.

As research in lighting continues, there’s confidence that the cost of LED lighting will go down, and their quality as grow lights will go up. Completely new technology is emerging as well, so-called FIPEL™ Panel Lighting is supposed to hit the market some time next year.

The moral of the story is small-scale growers should stick to HPS lighting if they want to save money, with double ended bulbs being the best option for higher wattage fixtures, say 1000 W. For larger scale operations, a careful layout of the garden and its lighting is essential and can save a grower thousands in electric bills.

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