I believe that it was David Packard who first described this application for his Master theses.
And the HP200B Audio Oscillator actually used this concept for stabilization.
Luxeon have very expensive and very powerful wide-angle LEDs.
The little LEDs in my solar garden lights have an angle of about 140 degrees.
I have never seen little ones sold except cheap Chinese ones on E-Bay.
The bulk of 'ordinary' LED's is the packaging. The leads themselves are like 10 times or more the size of the actual P/N junction. If you send a REALLY tiny amount of current through a white LED and look down into the top of dome you can even see the fly wire that comes off one of the junctions. And the viewing angle is better cause they don't put the P/N junction in that little cup like that do on typical 5mm LED's.