Tower258 Posted August 15, 2021 Share Posted August 15, 2021 Hey all, So I'm a total nerd and went down a 2 day rabbit hole when I decided to do DIY lights for my 60 Hex project. My big thing is that I had no idea how bright "low", "medium" or "high" light actually was. When I looked it up, I always found vague lumens/gallon or just PAR values. Because I don't want to spend the money on anything that gives a PAR values, I had to figure them out. Most common white LEDs are phosphor-converted type LEDs and they all have a similar spectrum assuming the color temp is the same. This is why this can be done without knowing the specific spectrum of the LEDs you are using. The equation is as follows: PPDF=Fa(lumens/(H(Tan[Φ/2])) (PPFD is what we think of as PAR) Lux*Fa=PPFD Fa-factor from reference link Lux=lumens/area Area= Pi(B/2)^2 B=2H(tan(Φ)) H-Hight of light from substrate. Φ- angle of LED reflector (total angle from side to side) Phosphor LED factors based on color temp; Less than ~ 3000K = 0.017 Between ~ 3000K to 4000K = 0.015 Greater than ~ 4000K = 0.014 Because this is an estimate, I plan to also estimate the angle of the LED reflector, thought down lights will sometimes give them. A source of error in this method is that it assumes 100% of the photons emitted from the LED will hit within the designated area (This also assumes the reflector will absorb no light), Therefore this estimate will likely be on the high side. The equation is best used for a single light, however, if you have a few that are close together it could still be an alright estimate given that the distance between the lights is relatively small compared to the area they are shinning on (most LEDs use this idea). If they are far apart, you can add the values where they overlap (like a Venn diagram). This equation could be changed to estimate a light bar by using B to find Area with a different equation. I'm tired now but will show this if anyone has interest Hope this helps someone save a few bucks! Who says you'll never use trig after high school? 2 Link to comment Share on other sites More sharing options...
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