Led Buyers Guide What to Look For and Why

The purpose of this thread is to help us decide what we want when we’re buying an Led light and why. First off let’s focus on some lighting terminology so we understand what we’re looking at when we read a lights specs. These are general definitions and I encourage you to research each term further if you would like to know more.

PAR stands for photosynthetically active radiation and is a measurement of how much light is available to the plant for photosynthesis, between the 400-700nm wavelengths.

PPF stand for Photosynthetic Photon Flux and is the total amount of PAR a fixture produces and is measured in micromoles per second or μmol·s-1.

PPFD stands for Photosynthetic Photon Flux Density and is how much PAR is reaching your canopy per square meter per second.

μmol/J stands for micromole per Joule and is a measurement of the efficiency of a light, be sure to check if your looking at total fixture efficiency and not just the diodes without the driver attached.

The next thing we’re going to look at are TRUE watts, which is a measurement of how many actual watts of electricity the fixture draws from the wall. It’s not uncommon for a light to misrepresent how many watts it draws especially if your shopping Amazon ect. (Most new buyers will go by watts if they don’t know about the other terms we discussed resulting in inflated claims to attract buyers).

Example of why efficiency matters for sizing your light : 100 watt light with 3.0 umol/j will produce twice as much PPF as a 100 watt with 1.5 umol/j.

Blurples vs “Natural” spectrums: Blurples are made with only red and blue LEDs and give off a “blurple” looking light. These originated from an outdated understanding of what spectrums of light plants use for photosynthesis. We have since found out that plants use more than just red and blue light for photosynthesis and I would recommend against getting a “blurple” light. Mainly because they make it extremely difficult to diagnose minor plant and pest problems compared to lights with a more “natural” spectrum.

Red Vs Blue diodes and why different spectrums have different efficiencies. You may be looking at a light fixtures specs and notice different efficiencies for different spectrums on the same type of fixture. Blue photons are more energetic and require more energy to produce then red photons making red light more efficient to produce then blue.

What about UV A and B (280-400)and Far Red (700-750nm) diodes? As technology and research progresses we are finding that both of these wavelengths have an effect on our plants. UV in particular UVB in small amounts has shown promise in increasing terpene and cannabinoid levels. Currently the most efficient method of producing UVB are dedicated UVB specific fluorescents. There is a ton of info about UV and when to add UV at what amounts if you ever wish to do some further research on lighting spectrums and how they affect growth and shape of plants I highly suggest looking into a few videos of Dr. Bruce Bugbee. Adding a certain amount of far red into the spectrum has been found to increase photosynthesis in comparison to a light that produces the same amount of light with no far red.

Warranties: 3 years is common, 5 years is good and 10 is very rare. The led drivers may have a seperate warranty period then the diodes depending on the company.

DLC Listing: Design Lighting Consortium is a non profit that verifies the specs of various LEDs. I highly recommend DLC listed fixtures as they have independently tested the lights and their results are free for all to view at https://www.designlights.org/

How much light do I need? Plants in Veg can use upto 600 PPFD and 1000 in flower without CO2 if everything else is perfect. If you are using CO2 you can go upto 1500 PPFD at 1500ppm but it is recommended to start at 1000 PPFD and 1000ppm and match the levels as you increase slowly to gauge plant response.

PAR Maps: when PPFD is measured at canopy level at a certain height in different areas to show light spread. QBs often concentrate more light toward the middle of the canopy then bar style LEDs.

COB stands for Chip on board and typically have less even light distribution than regular diodes.

Why do 2 fixtures with the same specs cost different amounts from different manufacturers? Things like branding, advertising, warranty, the company’s reputation and the research the company does on their products can all affect pricing. Consider what fast and reliable warranty service and replacements are worth to you. You may prefer to pay a bit extra for a fixture from a domestic distributor rather than chance waiting weeks for a replacement from overseas.

Internal fans vs. heatsinks: most high quality modern LEDs have heatsinks rather than internal fans because it takes power to run the fans reducing the lights efficiency.

Sizing LEDs may require a quick look at a products PAR chart if you are unfamiliar with similar spec LEDs. Make sure the chart fits your required canopy space and that the PPFD levels are acceptable for your stage of growth. It can be a good idea to get slightly more light then you need if the fixture is dimmable to the required levels because LEDs will produce slightly less light as they age. If the par chart notes that there are no reflective walls used in the test then you will have higher PPFD values especially along the edges if you are using reflective walls.


You have a ton of reading materials here. Morning coffee reading time!

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As Led technology progresses we will see even more commercial growers making the switch from HPS. The technology is advancing fast and new products are hitting the market all the time. And most high end LEDs will actually give a better ROI over time then a HPS. There are no bulb changes, power savings are substantial and they require less HVAC during use.


@treetrunks/@Slym3r very concise and specific information for analyizing and comparing available lighting fixtures…Thanks for you efforts and contributions !!!


I was gonna say its a good thread and we needed it. Its hard to explain to folks when they dont understant and we may not give the correct answers because we didnt understandbthe question because it was asked wrong? That make sense?


Great study about light levels and yeild in cannabis, research done by Jim Eaves at the University of Lavel in Canada. Attached is a link to his study courtesy of @indoorgardenshop


Cannabis can also be vegged in light levels over 600 ppfd and can become more compact with shorter node spacing