[Steve Smith]

Yes they can, and they do.

Manufacturers of dichroic filters think otherwise.

http://www.thorlabs.de/newgrouppage9...ctgroup_id=986
http://www.jnsglass.com/dichroic.php
http://www.uqgoptics.com/product_cus..._dichroic.aspx
http://www.oceanthinfilms.com/produc...hro-light.html

Beseler and Durst think otherwise too:

http://www.beselerphoto.com/light-sources/
http://darkroom.ru/info/manuals/durs...manual_eng.pdf


Steve.