This is how I did.
1. create a startinglights.ini in your track data folder, like this for example:
2. For the actual meshes they should be named KS_START_LIGHT_0, 1, 2, 3, 4
3. material name I have set is semaphore_AT although I'm not 100% sure if the name matters
4. texture used named as semaphore.dds. It is the lens of the light
5. in sdk use the ksPerPixelAT shader and other normal settings.
That creates 5 lights that light up one by one and then turn off when the race starts.Start lights don't work in replays iirc.