Why must light intensity be low for bright field microscopy of oral epithelial cells?

[superwolf]

What is the approximate size of epithelia cells from the human oral cavity? And why must light intensity be low when studying them in bright field microscopy? (I know that phase contrast is better).

 

[Andy Resnick]

Cells obtained by a 'cheek swab' are large- 30 microns across, easily. Now, in vivo (and in cultured monolayers), the epithelial cells pack together and present a cross-section closer to 10 microns.

The intensity doen't need to be low, exactly- what is important is to filter out the IR part of the spectrum and prevent dry-out. Even so, too much light is damaging to cells- not cancer, but photodamage can occur.