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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
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.
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.
