The classic textbook on optics is
Optics, by Hecht and Zajac, but this covers very fundamental materials about the properties of light and does not really go into applications and spectroscopic or microscopic instrumentation (at least, my version doesn't). There are also textbooks specifically dedicated to microscopy, of course, though I cannot with confidence recommend a good one. Olympus has a great website with some basic primers on various topics:
http://www.olympusmicro.com/ . Actually, they seem to have expanded it quite a bit since the last time I visited it. I found this website very useful back when I was building a single-molecule confocal fluorescence system on my own. Some applied spectroscopy textbooks also have some introductory material, such as Lakowicz's Fluorescence Spectroscopy.
But, as Borek mentions, any text related to spectroscopy, microscopy, or optics is going to be pretty heavy on the math, unless you are just interested in applications. It is a fundamental discipline of physics, after all.
NOTE: I looks like later versions of Eugene Hecht may have dropped Zajac as a coauthor. My version is from 1974. Thankfully I don't think a lot of the fundamental stuff has changed in the last 30 years.