Colors using black body emission?

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Colors using black body emission?

Postby buzby » Thu May 16, 2013 2:51 am

buzby Thu May 16, 2013 2:51 am
Ahmed,

I am trying to match this picture and am having trouble with the lighting. As you can see the light is washing out due to the brightness yet it is not covering the area of the wheel.

The actual picture is taken of a device with 6 LEDs inside aimed out at the wheel at a 90 degree angle from inside the BMW cap. DO I need to create 6 IES LED lights and put them inside the model or can I get away with a blackbody emission? Also how do you change the color of the blackbody emission. I tried the temperature but it is not enough. I want the color blue like in the actual photo. Thanks for all your hard work!
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Last edited by buzby on Thu May 16, 2013 1:03 pm, edited 1 time in total.
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Re: Colors using black body emission?

Postby roeland » Thu May 16, 2013 5:43 am

roeland Thu May 16, 2013 5:43 am
A blackbody emission and a texture emission are almost the same, the only difference is that a texture emission has a flat spectrum by default instead of a blackbody spectrum. The best way to simulate a LED is to use texture emission and change the texture/efficiency input to a gaussianspectrum. You can load an IES file into the distribution input by changing it to a floatimage.

To simulate a blue LED, set the wavelength slider around .25 and the width to around .015. A larger width gives less noise, but if it is too large you get less saturation.

You can also use a RGB color, but you will also get slightly less saturation than with a gaussian.


Mathematical background: Octane uses these formules to get the Gaussian distribution:
μ = 380 + 340 * wavelength (so it goes from 380–720nm)
σ = 800 * width.

You can look up the wavelengths of various LEDs on the internet. For most blue LEDs the wavelength is 470nm (set the wavelength slider to 0.265).

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Re: Colors using black body emission?

Postby buzby » Thu May 16, 2013 1:01 pm

buzby Thu May 16, 2013 1:01 pm
roeland wrote:A blackbody emission and a texture emission are almost the same, the only difference is that a texture emission has a flat spectrum by default instead of a blackbody spectrum. The best way to simulate a LED is to use texture emission and change the texture/efficiency input to a gaussianspectrum. You can load an IES file into the distribution input by changing it to a floatimage.

To simulate a blue LED, set the wavelength slider around .25 and the width to around .015. A larger width gives less noise, but if it is too large you get less saturation.

You can also use a RGB color, but you will also get slightly less saturation than with a gaussian.


Mathematical background: Octane uses these formules to get the Gaussian distribution:
μ = 380 + 340 * wavelength (so it goes from 380–720nm)
σ = 800 * width.

You can look up the wavelengths of various LEDs on the internet. For most blue LEDs the wavelength is 470nm (set the wavelength slider to 0.265).

--
Roeland

Brilliant thank you Roeland! I have the settings correct and the power way down low but I cant seem to get the area lit without the light blowing out at the center. Can you see any adjustment I might make?

There is still no comparison to the original photo. I may end up having to create the 6 LEDs and aim them out like the actual picture
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