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I'm trying to use IES file which is 4FT light source and Cycles renders a reflection of it as a simple spot. If I try to use that IES on Area light instead of Point light to get an actual 4Ft rectangle, IES data simply doesn't work and it just is a regular Area light. As far as I know IES only works with Point lgiht source anyway. In comparison I used the same files in 3Ds Max and it reflects a proper rectangle. Are IES lights simply broken in Blender?

Thank you

3Ds Max Correct Reflection Cycles Incorrect Reflection

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2 Answers 2

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Problem solved. I used a simple mesh and applied emission to it with IES. But mesh itself should be exactly close to IES parameters. For example 4'x2" rectangle. In that case IES texture is displayed correctly. If your mesh is different from what IES is supposed to cover, you won't get right result.

enter image description here

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  • $\begingroup$ Hello :). As far as I know, mesh lights don't support IES profiles. To use IES, you need to connect them to the strength input of your point light. $\endgroup$
    – jachym michal
    Sep 18, 2020 at 5:26
  • $\begingroup$ Hi. that doesn't produce right reflections. It reflects a point in that case even if IES it a rectangle or something else. I consider it a lack of functionality that Blender has. $\endgroup$
    – Nebular Dust
    Sep 18, 2020 at 15:01
  • $\begingroup$ Good to know, I'm no expert on IES lights in Blender :). $\endgroup$
    – jachym michal
    Sep 18, 2020 at 15:02
  • $\begingroup$ I also don't think you are right on mesh lights. I can clearly assign IES to a mesh light and it does change the output. It's just a matter of using the right mesh. $\endgroup$
    – Nebular Dust
    Sep 18, 2020 at 15:20
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Recently I've been using blender for my home lighting design. I also ran into the problem of rendering the lamp reflections correctly. After looking at blender's source code I found that the IES Texture node uses the normal as the input vector by default. For point light, spot light and sun light, it is the vector of light ray. But for area light and mesh light, it is the normal of the surface. Therefore, using the default input of the IES Texture node directly, both area light and mesh light will provide results that do not match the IES data. By using the incoming output of the Geometry node, we can get an IES area light.

BTW: the strength should be 1/pi for area light and 1/(4*pi*projectd-light-emitting-area) for mesh light.

On the left is the point light, and on the right is the area light with IES data. I have used false color to compare the illumination of the different implementations.

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