Cooking

A lens gently cooks under an LED lamp.
This particular model, though not the rarest kind, is still very sought after. 
The glass has a yellow tint as the manufacturers, back in the 60s and 70s, used radioactive materials which were incorporated into the glass. As the radioactive materials decay, the yellow tint appears. All for the sake of quality and performance. 
Prolonged exposure to bright light will fade the yellow, but it's very difficult to get them back to the clear original. Some folks prefer them with the yellow tint, and will use them as is. 
I'm told they're not hazardous, as long as you don't grind the glass down and eat it. No plans for that at this time. 
It's a beautiful bit of kit, and my quandary is whether to sell it, or keep it. The jury's out.