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'White' LED light produced by most integrated white LED packages is in fact a mixture of blue (~460nm), produced by the LED itself and a broad-band yellow (560nm), produced by a secondary phosphor, typically directly coating the semiconductor that emits the primary light. The net effect is a single-source mixed-wavelength light. The eye does not immediately notice the dip in the spectrum around the green (notably, the eye is in fact tuned into green for maximum sensitivity so the spectrum 'appears' smooth to us when in fact it's anything but). These LEDs are awesome for many applications and they indeed do not generate as much heat as incandescent lightbulbs do, but several folks I know have noted that their eyes are more tired after viewing LED-illuminated samples under a microscope. http://powerelectronics.com/power_management/led_drivers/Fig-2-white-LED-vs-RGB-LED-spectrum.jpg Other types of 'white' LED lights employ carefully balanced mixtures of three primary colors, each produced by a separate quantum well. Unfortunately these lights tend to shift colors with temperature and with age and appear different from different angles - feedback compensation is required for precision use. These tend to be much easier on the eye (at least to me), but I am not sure whether any scopes come with these composite LEDs installed. Artem On Sun, Jan 23, 2011 at 7:35 PM, Kevin Corbett <[log in to unmask]>wrote: > Hi everyone, > > I'm looking to buy a new stereo microscope for looking at crystal > trays, and was wondering if anyone could help me answer a few questions: > > 1) Does anyone have experience with LED illumination in the microscope > base? I'm worried that there might be excessive heating of the base, as this > is a huge problem with integrated halogen lamps. Also, can these stands with > LED's accommodate polarizers? > > 2) Any really good (or really bad) experiences with specific > manufacturer/models? > > Any advice is much appreciated. Thanks very much, > > Kevin > > Kevin Corbett, Ph.D. > Stephen C. Harrison Lab > Harvard University Medical School > corbett (at) crystal.harvard.edu > (617)-432-5605 >