If you say it's on the inside it could just be dust. There are air vents to let condensation out.
If so, the easiest way to fix it is to remove the bulb and use the hole to clean out the inside with a rag on a stick. Someone sent me a nice tip of using a remote cable operated grabber with a towel wrapped around it.
If so, the easiest way to fix it is to remove the bulb and use the hole to clean out the inside with a rag on a stick. Someone sent me a nice tip of using a remote cable operated grabber with a towel wrapped around it.

