Hello Radiance community,
I’m trying to reproduce a luminaire similar to a LED strip light. I’ve attached a reference (link) because I’m not sure if “LED strike light” is the correct term. The idea is to simulate, on one hand, two meters, and on the other, 30 centimeters of this LED strip using an .IES file (for example, link).
It’s my first time working with this kind of artificial lighting, so any comments or help would be very welcome.
Juan Manuel
Hi Juan,
Did you mean “LED strip light?” I have never heard of a “strike light.”
In any case, the photometry indicates this device has emission very close to Lambertian, so you may not need to use the IES file if you are OK with a few % of error.
To model a Lambertian emitter, take the total lumen output and divide by pi and the area of the surface. For example, let’s say the 4000K unit is 12 inches by 0.3 inches. (I couldn’t find the actual dimensions of it.) The total flux output is given as 1126.4 lumens. So, we calculate:
emmiter_luminance = 1126.4 / (3.1416 * 12 * .3 * (0.0254 m/in)^2)
which gives you about 15437 candelas/sq.meter. To use this value in Radiance, divide by the standard efficacy of 179 lumens/watt to arrive at 862 watts/sr/sq.meter. Your scene model would then be:
void light LED4000K
0
0
3 862 862 862
LED4000K polygon strip
0
0
12 0 0 0 0.3 0 0 0.3 12 0 0 12 0
I’m assuming in the above that your scene distances are inches and the strip is directed towards +Z, but of course you can adjust this to whatever you prefer. It does not affect the “light” output radiance of 862.
In fact, you can make your strip any length at this width and it should still work, so long as you don’t change the width from 0.3 inches. The total output will adjust with the length. You may also take one short strip and make an array using “!xform -a 5 -t 0 12 0 strip12.rad” or similar.
I tried using ies2rad on the file provided, and it lacks appropriate dimensions for the strip, so it would require some effort to make this work properly with that method.
I hope this is useful.
Best,
-Greg
Hi Greg,
Thanks so much. As you mentioned, I was asking about an “LED light strip”. I found all the information very helpful. I’ll work on it and let you know if I run into any problems. Thanks again for your help!
Best,
JM
Hi Juan, sorry for this very late reply…
Just one more note. If you need to resolve the individual LEDs, you can combine a continuous illum surface (that will illuminate diffusely reflecting surfaces) parametrized according to Greg’s reply with small glow polygons, that match the size and luminance of the individual emitters (and will produce small, bright sources when seen from nearby). The approach is similar to the good old modelling approaches with IES descriptions modifying the emission of an extended (but invisible) illum surface that covers a more detailed representation of the (glow) luminaires.
For distant views and anything covered by a diffuser, this is obviously not necessary/useful.
Best, Lars.
Hi Lars,
Thanks. I’ll keep that in mind. I think it could be very useful for rendering the LED strip in a shot with the camera positioned close to the light, as you mentioned. Thanks again for your help!
Best,
JM