Please correct me if I’m wrong but I have not seen any LED grow light sellers that list the total micromole output of their fixtures. Most all HPS sellers with DE bulbs list 2100 micromoles as the total output of photons from the bulb. Of course this will be reduced by the reflector somewhat, but a buyer knows what they are dealing with.
I see claims for what size HPS that LEDs will replace but that does not instill confidence in the purchase of these relatively expensive lights. As a buyer, I want micromoles!
There are much more qualified people already tagged and responding, but yes, the legit LED manufacturers do publish this info. Make sure it is reported in µmol/s.
We believe it is also important to understand how total µmol output is measured, and how to interpret these measurements in relation to Coefficient of Utilization (CU), which is a metric that describes how much of this total output will fall on the canopy under the fixture.
Total PPF output is most often measured in an integrating sphere or a goniometer / goniospectrophotometer. These instruments quantify light emitted by a fixture in all directions, while flat plane measurements are more specific to the light that falls on the canopy. There are pros and cons with each measurement technique; for example flat plane measurements are affected significantly by the color of the walls and may not accurately reflect light intensity in an array of fixtures.
Assuming that the total output of the fixture actually hits your canopy would be incorrect, as one has to account for the angular distribution of light, or the shape of the beam so to speak. We use Coefficient of Utilization (CU) to describe how much light from a fixture hits a canopy of a certain size at a fixed distance between the fixture and canopy.
We have a blog post about CU that we are working on, but in the mean time, check out this visualization of Coefficient of Utilization of our FluxScale fixture with and without our reflector, on a 4.5’ x 4.5’ canopy, at a height of 1ft, 2ft, and 3ft. This shows the importance of understanding how many lights work together to illuminate the canopy in large scale grows.
Food for thought, are there any quick calculators or equations that can be done to take known measurements given by a company to figure out any missing measurements? Or does that data need to be provided directly from the company?
And a Devil’s Advocate question, is it fair that all the testing data on these numbers be provided by the manufacturer directly? Can the numbers be skewed some how on purpose (beyond normal variance? Is there allowed percent of error in the numbers reported?)
Thanks everyone for the great feedback. I checked the Growers House website and was able to find PPF listed for about half of the manufacturers. The main reason for wanting to see this was to be able to compare how many photons are possible to capture for the amount of electricity used and capital cost. It is universally accepted that LEDs are more efficient than HID lights. The only way to know how efficient they are is to know PPF and divide by electrical watts.
So thanks to everyone for making me read the LED ads more closely.
Sorry for jumping in late, but sounds like you already found what you’re looking for. We list PPF for all of our fixtures on our website in case you weren’t able to find elsewhere. And your approach to dividing PPF by Watts is efficacy (measured in umol/J). It’s a great metric to get a snapshot of fixture energy efficiency, but as others have noted it’s a limited metric if used in isolation without considering CU and other critical factors to overall performance (and efficiency). For example, it’s easy to achieve a very high efficacy with a low-performance and low-wattage fixture with a narrow band spectrum (kind of like an automaker can achieve a high MPG vehicle but typically they are slow and small).
Thanks so much for the reply. It seems that I just know enough to be dangerous but I like getting on this board to see if my perception of things is correct. It would appear that LEDs have an advantage in that if measuring PPF in an integrating sphere the measurement already includes the efficiency of the optics whereas the HPS bulb PPF does not without putting the whole fixture in it. So the claimed PPF of 2100 must be reduced to allow for the efficiency of the reflector. Bugbee’s paper did this I think and came up with about 1750 micromoles that actually escaped from the fixture.
One last point, I think Bugbee’s paper showed that the harder one drives an LED the higher the output and lower the efficiency. Also, blue and red LEDs are more efficient than white or UV. As a buyer it is important to see if the manufacturer produced less photons to achieve a high efficiency, loaded the fixture with only blue and red diodes or advertised a high efficiency and don’t tell you the micromole output. Please comment to test my understanding.
Yes - you’re on the right track when comparing PPF/PPFD from an HPS bulb vs and LED fixture. PPF is a good measurement when comparing one HPS bulb to the next, but not when comparing to LED fixtures. Really what you want/need to know is the PPFD a fixture will produce over your crop canopy and the required energy (watts) to produce it.
Yes, red and blue are the most energy efficient wavelengths of light to produce. So a red/blue “blurple” spectrum will be more energy efficient than a broad spectrum light which includes other wavelengths. Now, the ultimate measure of efficiency is dependent on the yield/quality of crop produced per KwH so if a “blurple” fixture is more energy efficient but produces a lower yielding or lower quality crop than a broad spectrum counter, then it’s not more efficient in the end. The subject of light intensity and spectrum on plant growth and development is a highly researched topic.
Some great responses, pardon us jumping in late here!
PPFD measures the number of photons in the 400-700nm range of the visible light spectrum that fall on a square meter of target area per second, and certainly this is the primary metric that every grower should be focusing on in regards to the quality and efficiency of grow lighting.
However, the PPF metric does not factor in the quantity of photons lost to aisles, walls, and spaces between the plants in your facility. That being said, beware of the footnotes—or the lack of them. More specifically, the distance between the grow-light itself and the plant needs to be factored into the equation, as you want to know not only how much light is released from the fixture but how much of it is actually landing on and being consumed by the plant. So, when evaluating your grow light options look at the distance at which this metric is derived…it should be the same.
We’ve been doing a lot of research and development with advanced optics to control the beam spread of our lights, getting a more directional focus on the plants themselves and avoiding light loss, something we detail on our website if you’re interested.
