HDRI vs Mesh Lights

Leonides02

So, general question: 

I have a powerful PC (3x GTX1080 TI), a big upgrade from my previous 2x GTX 970. Renders generally happen very quickly.

However, HDRI renders always take less than a minute at even very high resolution. However, with the addition of mesh lights or (for instance) iRadiance's Light Probes, renders take much longer. This happens primarily with indoor scenes, but also when I combine HDRI environments with meshlight to simulate specific lighting.

My question is why do mesh lights take so much longer to render vs HDRI environments?

Thanks!

DimensionTheory

My light probes shouldn't be taking any longer to render than HDRIs in the same scenes because they are HDRIs themselves.  Mesh lights take long because the renderer has to run different lighting calcuations that take the shape of the geometry into consideration, textured mesh lights more so because geometry and surface normals then have to be multiplied by the texture's intensities.

Leonides02

You're right, I was thinking about your HDR Mesh Lights. :)

Thank you for the explanation!