Angel eyes originally came in BMW's.Now they are considered rice by many(not me though)
Basically they are a ring of glass/plastic with cuts behind them to refract the light, which lights up the whole ring.
They by themselves have nothing to do with HIDs.You can get them installed even if your car has reflector housings.
The BMW use a 5Watt halogen bulb to light up the rings/angel eyes and that is the reason they are very bright.
Most of the angel eyes found on after-market projectors use one or two LED's and hence their output is feeble.Using LEDs is not advisable as LED fail when exposed to high heat(mostly in headlight housings).That is the reason why people have to get the LEDs replaced in the rings after some time because the heat from the main headlight bulb(low beam/high beam) cause the LEDs to fail.
Thats all I can think of now.
Thanks for the compliments