LED or HID? The Future is Looking Bright

by | Apr 9, 2019

The debate has been ongoing for years. It’s quite likely that, if you are making initial design plans for your grow facility, or even if you are currently in operation and you’re looking for alternative lighting, you’ve been faced with a few questions. Are LED lights the right choice for me? Do they perform as well as traditional HID lighting options such as metal halide (MH) or high pressure sodium (HPS)? Is it worth the upfront cost? Undoubtedly, the initial sticker shock can have you turning the other way without mindful consideration. But let’s look at all factors before we make such hasty decisions.

led lights, LED or HID? The Future is Looking Bright

First, let’s just address the most looming concern with LED lighting options. Depending on what specific lights you are comparing, choosing LED lights may mean increasing your initial lighting investment by 200-400%. Now take a breath and look beyond this initial purchase and this is when we begin to see how such an investment may be well worth it.

Over the course of many years, LED technology for horticultural use has come a long way. Certainly, there will continue to be more advancements in LED lighting. Many of the top LED lighting manufacturers have run endless trials of spectral quality and output optimization. In fact, cannabis cultivation alone has been a significant motivating factor for advancing this lighting technology. Lights like MH and HPS were adopted a long time ago for indoor cultivation, and while even this technology has come a long way, it has still been met with limits. Ultimately, they use high powered ballasts and lamps that generate excessive amounts of heat. Efficiency in LEDs means that you can meet the same light output at a lower wattage.

However, it doesn’t end at intensity. While intensity is very important for overall plant growth and development, just as important is the actual light spectrum. You may notice the market has been flooded with cheap LED options, largely in the consumer markets, but the commercial markets have been subjected to this as well. Many of the more reputable LED lighting manufacturers have put a large focus on optimal spectrum. Some even include variable spectrums that can be adjusted throughout the grow cycle. The spectral quality can affect shoot length, bud development, leaf size, cannabinoid, flavonoid and terpene production. Be cautious of any lighting manufacturer that insists on omitting much of the spectrum and overemphasizing purely red and blue diodes, especially if they promote said lights as “full spectrum”.

led lights, LED or HID? The Future is Looking BrightSo, onto more pressing matters. Is this investment worth it? If you break down the numbers we can certainly see how it would be worth it. Consider that lower wattage, means lower energy, thus less thermal output for the same light output. So, while there is operational cost savings due to wattage alone (roughly 40% less energy usage when comparing leading brands in both markets), the true savings comes from decreased BTU output that can be credited to the lower wattage, which means BTU output follows in tandem with the 40% reduction. This means much less load on environmental cooling systems. For anyone familiar with operating costs of an indoor cultivation facility, you will know this can make a dramatic difference in recurring expenses and operating costs. On a final note, quality LED lights, as mentioned before, have a more desirable spectrum over lights such as HPS, which means the energy being used will be more appropriately applied to plant development, rather than spikes in the spectrum that are less desired.

Yet another benefit to utilizing LEDs would be for vertical grow systems. These types of grow models are gaining in popularity. For instance, if you use a two-tiered vertical grow design (whether it be stationary racking or mobile racking systems), this means you are doubling your canopy space while utilizing the same square footage. It doesn’t take much imagination to see how such a model would be extremely valuable. Utilizing HIDs with high thermal output just simply aren’t accommodating for this model and could be extremely problematic.

The yield potential with the latest LED technology has been credited for keeping up pace with HID lighting, possibly giving a slight edge to double-ended HPS. All things considered, this difference is negligible when given the operation cost savings. Choosing the appropriate lights for your operation is certainly something worth investing time into considering. When considering LEDs, don’t just focus solely on the sticker shock of those upfront prices, but look into the future and consider, not just your ROI, but general longterm operating cost reductions.


Now let’s just take a quick moment to give a brief rundown of some lighting terminology that will assist in making informed decisions. And remember, “Lumens are for Humans”…in other words, it’s not an appropriate measure of light quality or concentration for plants as lumens are a measure that are favorable to the human eye. The same goes for lux and footcandles.

PAR (Photosynthetic Active Radiation) PAR describes light within the visible range of the spectrum between 400 and 700 nanometers (nm). It’s often mistakenly used as a measure of light, but this is not accurate as you will see with PPF and PPFD.

led lights, LED or HID? The Future is Looking Bright

PBAR (Plant Biologically Active Radiation)
Discussions of PBAR have become more prevalent in recent history. Especially in the realm of cannabis where we discuss the effects of UV and IR on flower initiation and development as well as cannabinoid and terpene productions. PBAR extends the usage range outside of the standard PAR considerations. Between 280-400nm on the ultraviolet range, and 700-800nm in the far-red range of the light spectrum.

PPF (Photosynthetic Photon Flux)
PPF is a measure of how much light within the PAR spectrum that is being emitted from the light source every second. This is measured as micromoles per second (μmol/s). When discussing lighting efficiency, this is the number used (PPF/Watts=μmol/joule).

PPFD (Photosynthetic Photon Flux Density)
Aside from considering spectral quality, this is the magic number to focus on. PPFD is the amount of light within the PAR spectrum that is actually reaching the plant. This is measured in micromoles per square meter per second (μmol/m2/s). For instance, most manufacturers will provide a recommend height from the top of the canopy. If you hang the light 12 inches above the canopy, the PPFD may read as 900 μmol/m2/s. This is how you know how much light is actually reaching the plant. Height or intensity (in the case of dimmable lights) can be adjusted by utilizing this metric. Hours of light per day can play a role here as well, which is where DLI comes in.

DLI (Daily Light Integral)
The final consideration when it comes to light is DLI. DLI is accumulated light in a given day. This metric relies upon calculated PPFD throughout the light cycle. The math is very simple and this becomes a powerful tool in gauging plant needs and maximizing potential. PPFD x (3600 x photoperiod) / 1,000,000 = DLI To break this down; photoperiod is the hours of light given to the plants per day (typically 18 hours during vegative growth and 12 hours during flowering), 3600 is the amount of seconds in an hour and 1,000,000 is the amount of micromoles in a mole, as DLI is measured is Moles/day. The general recommendation for cannabis (though there can be genetic variability based on region of origin, in other words, some cultivars may have varied light saturation levels, be it more or less) is a DLI of 40 moles. Due to light saturation, you are met with points of diminishing returns. Any light accumulation above this would rely on adjustments of ambient temperature and CO2 levels. So, let’s say your crop is getting 900 μmol/m2/s for 12 hours per day. 3600 x 12 = 43,200 x 900 = 38,880,000 / 1,000,000 = 38.88mol This is a great range for flowering cannabis plants, which are considered a high DLI crop.

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