I was doing a little research trying to figure out how fast the lens would heat up, assuming it was 92% efficient i.e. would retain 8% of the energy passed through it as heat. I noticed that acrylic/PMMA has a glass transition temperature of at least 85 Celcius. The operating temperature of the diode is 55 Celcius. Presumably as long as I keep the diode under its operating temperature the lens shouldn't overheat, then?
Obviously there will be little niggles like the acrylic isn't as thermally conductive as the metal diode case etc, but still, that seems like a big margin.