Why are 28 real time point lights faster than a lightmap?

Unity Engine
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1

I have been lightmapping my scenes lately to give the environment nice shadows using Beast, but now I am realizing that its costing me upwards of 15-20 fps just for lightmapping. In my current scene I have 28 point lights set to BakedOnly I used for the lightmap, with 4 texels per unit for lightmapping. The lightmap ends up as 1 1024x1024 lightmap and looks ok however the game only runs at 45fps on the ipad. Clearing the lightmap and turning those 28 point lights to RealtimeOnly make the game run at a solid 60fps.

What is the reasoning behind this? In the unity docs it says lightmapping is 2-3 times as fast as having real time lights, but in my case its a significantly slower than real time lights.

For reference I have tried both VertexLit and Diffuse Fast as shaders, and I see no difference in performance with either. However switching to Mobile Vertex Colored then drops my FPS down to 25-30. My scene has about 1.5k visible tris with 20-25 draw calls. Anyone have any advice?

2

Only the four most important lights per object get used when calculating vertex lighting. I’m not sure about the speed of light mapping, but there’s a chance it will get faster in 3.2.

3

Please check that you do NOT use Dual Lightmaps (on Mobiles).

4

I have no idea why, but now that I upgraded to 3.2 and changed all of my shaders to mobile vertex lit, the performance of my lightmapped scene is improved dramatically

5

We have optimized mobile shaders a lot for 3.2.