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LED lights for large grows

If LEDs really can make 2.4 umoles/J that is quite significant compared to the results from Bugbee’s paper. My question is how are the LED panels at producing a uniform flux over a large grow area? With HID, the reflector design is the key to achieving this.


@Fluence would you like to weigh in?

can I ask a question?

if a 300w light has a umol reading of 1950 from 12 inches wouldn’t the efficiency be 6.5 umols/J

I think the confusion is photon flux vs. total photons. The meters I am familiar with measure micromoles per square meter per second. When the meter measures 1950 that means the flux is 1950 umoles per square meter per second. If the aperture of the measuring device is 1 square inch then you can see that the total number of photons measured is really really small.

The calculation is 144 square inches per square foot and about 11 square feet per square meter so the photons you are measuring is 1950/(144 x 11). That will be the number of photons per second you are measuring.

For the umoles per joule is the total photons per second generated by the light divided by the number of electrical watts required by the light. As mentioned by another poster, you would need an integrating sphere to measure all of the photons being generated by the light. I’m thinking this is a very expensive device. A problem arises when manufacturers make claims about the total umoles of photons per second from their light they seem to know that no one will check on it .


Forgot to include my assumption that the aperture of the measuring device is 1 square inch. It is probably less than that but just assumed that for the purposes of the calculation.

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Im using a hydro farm quantum meter

this light really is impressive, with a spectrometer it has the same spectrum as the spydrx plus

and the meter reads consistent in a 2x2 area 1900 umols

thank you so much for helping me understand. now the way you explained makes absolute sence

Not sure about the 3.32 micromoles per joule as there is more variables to consider. However, the 1900 micromoles you are measuring over the 4 square feet is probably way to high for your grow. There are some technical papers out there that show the photosynthetic rate as a function of micromoles. The graph is pretty linear up to about 800 umoles. After that the curve starts to flatten out. The upshot is, above 800 to 1000 umoles of photon flux produces less increase in photosynthetic processes for the added amount of electricity used.

The upshot is you could double the footprint to 8 square feet and theoretically have the flux be 950 umoles. However, you will get more than half the growth.

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LED panels are fully capable of providing a much better uniformity than any HID fixture since they always employ a multitude of small point sources (each LED), as opposed to a basically single point source as in the case of HID. This makes uniformity much easier to achieve, without having to rely on reflectors to spread out the light beam and on high hanging distance to allow the beams from adjacent lights to blend more. In addition, LED can use secondary optics to further diffuse, spread and blend the light beams for even better uniformity. As a result, a well designed LED fixture can exceed the PAR uniformity provided by any HID fixture, and at much closer distance (less than 2 feet) to boot.


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Hey @kirkcollier, thanks for you question!

Two separate topics
• To address micromoles-per-joule: Bugbee’s research was conducted in 2014, and there continue to be significant advances in LED technology year-over-year. If you review the comments section of his paper, you’ll see he tested our VYPR system in 2016 which was the first broad-spectrum system to achieve over 2 micromoles-per-joule. Since then, we’ve increased our efficacy to 2.3 for broad spectrum, and well above for narrow band spectra.
• To address light distribution: this is not an LED v HPS questions/answer given LED systems can take nearly any shape and size with various optics… which pseudo answers the question: LED fixtures utilize factor and optics (beam angle) to achieve light uniformity. A narrow beam angle will distribute light in a condensed area (with higher PPFD in that area), whereas a broad beam angle will distribute more widely (with a relatively lower PPFD across the area – all things being equal). This is an oversimplification as both instances depend on mounting height above canopy to accurately determine uniform flux density.

Hope that helps!

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Thanks Fluence. We are using HPS and AC/DE reflectors which gives us about 22 ft2 or about 2 m2 of 800 umoles avg. Our bloom room consists of 32 of these lights. If I shop around this costs us about $420 per light. What does it cost for an LED light in a multiple light configuration to cover 2 m2 at 800 umoles? I think that is the question that many growers have before making the jump to LED technology.


Fluence Spydrx Plus for the win!


so 3.32 umols/J