Hi Kevin,

	We have 3 Olympus microscopes  with three different lighting options.  The three variations we have on our microscopes are:
 1. a microscope with a reflective light base (internal mirror) that reflects light directed into the microscope base from an external halogen light-box.
 2. a microscope with an integrated, low-power (30 watt) halogen light source (still has a mirror for the trans-illumination)
 3. a microscope with an LED light source

	In general, the LED light source in our microscope produces very little heat so crystal trays should be safe for viewing for quite some time without heating.  And, instead of a mirror, the base has a series of filters/diffusers to modulate the intensity of the light directed through the sample, or a "dark-field" filter.  That can be helpful.  However, the spectrum of light output by our LED light source is very blue (as opposed to the warmer "yellow-heavy" output from halogen or incandescent light sources).  I don't like the "cold", blue tones of the light and find that it contributes to eye fatigue.  I also find that this light doesn't offer as high a contrast for viewing certain drop conditions.  By that I mean that I occasionally find drop conditions for which I feel I can see differences in edge transitions or object boundaries better using the microscopes with the halogen light sources (i.e. comparing same drop with different microscope/light-source combinations).  This doesn't happen often and does not dramatically affect my ability to rate the drop, but it's notable to me.  In summary, I prefer alternatives to the LED light sources, but my dislike of the output spectrum is a matter of opinion.
	NOTE: My understanding is that the "blue-heavy" spectral output of white-light LEDs is a recognized property of LEDs (i.e. it's hard to achieve a true white light with LEDs).  However, the ability to produce LEDs that have a more natural spectra is improving and I know at least Olympus is very close to offering such a version (more $$).

	With regards to polarizers, we just use "screw-on" polarizing filters that attach to a channel/groove near the bottom of our objective lenses.  These are convenient and inexpensive (works with any light source).  They won't, however, fit on all objective lenses depending on the presence of the necessary groove.

-Andy Torelli


-----Original Message-----
From: CCP4 bulletin board [mailto:[log in to unmask]] On Behalf Of Kevin Corbett
Sent: Sunday, January 23, 2011 8:35 PM
To: [log in to unmask]
Subject: [ccp4bb] Stereo Microscope advice

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