We get asked every now and then about cleaning old light bars, and if its possible.
Whelen Engineering light bars now come with a protective coating, which makes the light bar easier to wash, and prevents the yellowing and hair line cracks we've all seen before on old lenses. Although on newer style LED bars we would just recomend purchasing new lense kits, it is possible to clean faded and yellowing lenses.
In our garage we often have customers come in, for example State Police, who still have some old rotators in service. To clean them, take some automotive "cutting compound" and a clean rag. Apply the compound to the rag and rub onto the lens, making circular motions until it turns into a light haze. With a second clean rag, wipe off the haze and the lens will be as good as new. We'd recomend a light coating of wax to help keep the clearity last longer.
Of course, at some point you'll want to think about replacing the light, and when you do we'll be here to help!