It can also assess the performance or efficiency of the light source, when compared to Watts. This measurement is used primarily to determine the actual brightness from a source of bare light. Lumens measure the flow of light, that is to say the total amount of light generated by a device. The first units of measurement was lumens, candela and lux. The units of measure have been refined and new ones were created to measure the light intensity used by plants. We understand better now how plants use light, and the technology has evolved enough to create quality horticultural LED. Until recently, the lack of light intensity in LEDs was a limiting factor for many gardeners and greenhouse growers indoors. I just thought it was easier to have the candela as the slider, because that’s the number you get when you measure with your lux meter at 1m distance, and the calculator does the conversion to cd/mm^2 for you when you put in the die area from the datasheet.Lumens, Lux, Candela, PAR, PPF, PPFD, DLI Units of measurement and terms to qualify horticultural lights.Įveryone knows what « Lumens » are from Physics class… But what about PPFD, PAR, PPF? If you want to do other LEDs that don’t have lambertian distribution you need to take a screenshot of the datasheet relative intensity graph, overlay it on the desmos calculator with some transparency, adjust the size so that it matches, then use trial and error to modify the cos() function until the orange line matches the image from the datasheet.įor tests done by people like koef3 and others, usually they list luminance (cd/mm^2) instead of directly candela, so you can just manually change the luminance to a number and then change the intensity to “l*s” and then you can adjust the luminance slider instead. If we do the CSLNM1.TG, we get 324.5 lumens from the calculator, again very close to the rated 325 lumens. Putting that into the calculator then gives 514 lumens, extremely close to the 515 spec. Here I used cos(1.025*angle) instead of just cos(angle) in order to make the function match the datasheet more closely: If we put 171cd intensity and 1.59*1.25 = 1.9875mm^2 die size we get 86cd/mm^2 and 537 total lumens.Īs I mentioned earlier this is a slight overestimate because of what you can see in the first image.Ĭorrecting for non-lambertian distribution: Here you can see that flat LEDs have almost a perfect Lambertian distribution (orange line), although the intensity drops slightly faster at large angles near 90 degrees, so the lumen numbers given by the calculator are a slight overestimate.īy setting the intensity (candela) and LED die size based on test or datasheet info, the luminance is calculated (cd/mm^2) and then you can adjust the min and max angles of light collection.įor example, the CSLPM1.TG has 171cd and 515 lumens at spec. If the LED does not follow the Lambertian distribution, a special function needs to be used instead of cos(). These LEDs have an intensity that follows Lambertian distribution, which means that the intensity of the LED is proportional to cos(angle), making it very simple to put inside the calculator. (but it can do other LEDs if you put in some effort) This works only for no-dome LEDs such as the black flat, white flat, or CFT90.
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