That sounds like a lighting manufacturer question. Dont remember the last time anybody tried to paint the light fixtures themselves. They have somekind of a baked enamel paint, super white or something of that nature.

Maybe Reflective Paint?

From wise-geek:

Reflective paint is a type of paint which contains thousands of little glass spheres, designed to reflect lots of light, even at night. It is most frequently used for signs on highways, but is also used on license plates, fishing lures, on mobile objects to be tracked (like a golf ball), or as an indicator on certain machinery. The size of glass beads ranges from application to application, but generally, the smaller the bead, the more expensive it is. The beads are sprayed on after paint is applied for the most even possible distribution. The beads are applied over a colored base coat designed to yield maximum reflectivity. A commercially available variety of reflective beads is 3M's Scotchlite product.

The typical glass beads used in reflective paint on highways are fairly cheap, about $5/lb. They are usually mixed with yellow latex paint. This paint is designed to be clearly visible when illuminated by headlights, but is often visible even without headlights due to ambient light. During the day the paint is bright, but not bright enough to be excessively distracting or blinding. Reflective paint is very useful because materials which glow independently, without constantly