08 Aug 2009, 02:30
Typically, only the higher-end LEDs used glass crystals. The great majority of the others used colored plastic. Many plastics, especially the colored acrylic usually found on the later models, degrades over time due to exposure to UV light and temperature changes [remember, these are a third of a century old, and counting!]. The damage takes the form of microscopic-to-mm sized fractures and fissures, and can give a cloudy or finely grainy appearance to the surface [it is the plastic equivalent of a cataract, and as such, is a degenerative condition, getting worse with age]. The microcracking actually propagates down into the body of the crystal, and except for very early stages, is not repairable by polishing. The plastic also becomes much more brittle and inelastic, and suseptable to shattering, even from a gentle impact, or mild pressure. Fortunately, there seems to be a fair stock of original replacements out there.