Are LED grow lights better than HPS grow lights for growing weed?
It's ten years since LED grow lights arrived on the market. However, the first LED grow lights promised performance they could not deliver. Many of them were not as good as the High Pressure Sodium (HPS) grow lights they replaced. This has left a legacy of doubt about the performance of LED grow lights.
How do LED and HPS grow lights compare today? Let's look at the current state of play with LED and HPS grow lights and answer the question; Which technology is better overall for the home grower?
LED grow lights deliver at least 50% more yield than the best HPS grow lights
In the last 5 or 6 years LED grow lights have doubled in light output per watt and more than halved in price. LED grow light companies have also become more accurate and consistent in the claims they make about their products.
LED grow lights are now between 50% and 300% more efficient than HID grow lights. Although the initial purchase price of LED grow lights are higher they pay back due to electricity savings in one year.
Which grow light spectrum is better, LED or HPS ?
There is a misconception that HPS produces a spectrum that LED cannot match. Some growers think that HPS bulbs are unique in delivering a lot of UVA and Far red.
This is not the case.
White LED grow lights with no added UVA or Far red LEDs output a similar amount of UVA and Far red as HPS. LED grow lights can even output a higher percentage of UVA and Far red than HPS with additional UVA and Far red LEDs.
Metal Halide (MH) and Ceramic Metal Halide (CMH) grow lights output a higher percentage of Far Red and UVA than HPS. However the MH and CM fixtures are less than half as efficient as the best LED grow lights. Growers wishing to replicate these spectrums can use LED grow lights with more added far red and UVA LEDs and spend a lot less on energy bills.
What produces a better quality harvest? LED or HPS?
In the last few years many independent tests have been done comparing the performance of LED and HPS. These are controlled tests where the plant genetics, light intensity, environment, nutrients etc. are kept the same but the light sources are different.
The five published and peer reviewed university studies are linked at the bottom of this article. Here is the summary of the results in terms of the cannabinoid levels in the plants grown under LED and HPS grow lights.
All published studies show the Cannabinoid levels of medicinal herbs grown under LED grow lights is the same or better than grown under HPS grow lights.
Dr Bruce Bugbee from Utah State university has also shared results of controlled tests of harvested flower potency under different grow light sources. He found no difference in the potency or herb grown under HPS, LED or MH.
At the time of writing we could find no evidence that HPS can produce a higher quality crop in terms of cannabinoid levels.
Does the added infra red heat emitted by HPS grow lights improve the harvest quality?
HPS has more Infra red radiation (heat radiation) which is 780nm and above. This is not photosynthetically active and will add heat to the upper canopy.
This will heat the upper buds to more than room temperature. This has been proven to cause secondary metabolites such as cannabinoids and terpenes to evaporate therefore reducing potency of the harvest.
This contradicts the theory that some growers get better results with HPS compared to LED grow lights because of the radiated heat emitted from HPS. It suggests the results are better with HPS because of poor optimisation of the LED grow light setup.
Cannabis strains were selected for performance under HPS lights for many years
This is of course true. Breeders have developed strains for many years under HPS lights. This may mean that the strains they developed perform better under HPS than other strains. However it does not prove the strains will perform better under HPS than LED. If the strains were not tried under LED spectrum how would you know?
LED grow lights can replicate HPS spectrum and eliminate this concern, if necessary. In addition breeders are now growing under LED as well as HPS for many years so the genetics will be adopted to LED spectrum and growing conditions.
The general recommendation for increasing terpenes and THC is to stress the plants in someway in the later stages of flowering. Stressing the plant with environment changes encourages the plant to produce its defence mechanisms. This can be done with irrigation, CO2, defoliation, environment or lighting stress. Here at MIGRO we recommend using a UVB grow light for a few hours in the last few weeks of flowering.
Conclusion of LED vs HPS potency
LED grow lights are much more efficient than HPS grow lights and therefore cheaper to own and run.
The spectrum of white LED grow lights is very similar to HPS spectrum and can fully replicate HPS with some added Far red and UVA LEDs.
All published grow tests of controlled comparison of LED and HPS grow lights find that LED grow lights produce at least the same quality harvest as HPS and often better.
Links to LED Vs HPS controlled studies:
Trial A: Photosynthetic Performance and Potency of Cannabis sativa L. Grown under LED and HPS Illumination link: https://www.scirp.org/journal/
