Check with your local DOT - here in Seattle you can report a light that won't change for a bicycle and they will fix it. They actually tune the sensors with a bicycle wheel.... Any bike with any metal at all on it should be able to change a light. It has nothing to do with steel - it's not magnetic, nor is it weight. The sensors in the ground operate by inductance - the are more like a metal detector. They are actually more sensitive to aluminum than steel....

Proper position can be crucial. If they haven't been paved over and you can see the sensor cuts its easy - for the circular ones you want your bike to be over the outside of the circle turning the front wheel to match the circumference usually helps. For the square type position your bike over the edge. For the square type with a center cut position your bike over the center cut. If they have been paved over hopefully the DOT will put markings down !

We also have a law that states if you wait a certain amount of time and the light doesn't change you can go through - this is for all vehicles, not just bikes and meant in the case of a broken light.