Cleaning LED boards

Not sure if this has been asked before, but how do you clean your LEDs and how often? I have 2xHLG 250r2 and 2x350r and I’ve never cleaned them for as long as I’ve had them.

Pretty sure 99% isopropyl alcohol (rubbing alcohol) and a soft, lint free cloth is most (all?) manufacturers recommendation. For god's sake, check my math and make sure but, like the alcohol, I'm about 99%. Lower concentrations (70% or 90% in the states) should also work. Make sure your light is off, unplugged and cool to the touch. Also, the yellow stuff (phosphor) is supposed to be there. Don't try to scrub it off