LED based ring lights are commercially available in a variety sizes from this company:

[www.srelectronics.com]

I have been using the 3200 model for about 6 months and like it very much. On the plus side, continuous light helps to compose and focus. On the negative side, even though it looks quite bright, it has less output than my Nikon ring flash (and thus means longer shutter speeds and/or large apertures with the LED light, which can result in decreased depth of field and greater chance for blur). It also sucks batteries surprisingly quickly (an hour a set) and the batteries left on continuous can get so hot you can barely touch them. Nonetheless, I now use the LED ring light for 95% of my macro work. White balance of the LED ring light is like an electronic flash.

Michael A. Learmonth, B.A.Sc., M.B.A., M.Eng., J.D., LL.B., C.F.E.I., P.Eng.
Senior Associate, Giffin Koerth Forensic Engineering and Science
40 University Avenue, Suite 800
Toronto, Ontario, Canada M5J 1T1
Phone: 416-368-1700 ext. 225
Fax: 416-368-5576