Sounds like you're talking about a headlight (or any type of a lightbulb with a reflector and a lens).
Instead of trying to simulate it using paint, why not make a miniature model of the real thing?
Easiest way is to drill out the front of the lamp and glue in MV lens of the correct size. Then if the reflecor is not supposed to be smooth, take a modeling knife and score some lines into the reflector.
Here is what they look like:
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Or google "mv lenses".
If you can't find MV lenses, drill into the front of the light housing, then apply Bare Metal Foil (or silver paint) to the drilled out area. When the paint is dry, apply a drop of epoxy glue to simulate the lens. Again, you can score the lens with a knofe to make it look more realistic.
If the lamps just have a thin slit in them, just paint the lens over just leaving a slit exposed.
This will look like a real lamp.
Peteski