Absolutely loved this book and the material. I would say its a fairly simple book and sometimes I wished for more, but I found that most things explain themselves if you read and understand the text, which is easy to do because it is well written. I used this for an introductory biophotonics / pseudo-graduate class and it worked well, it was one of my best classes I've ever taken.
This is a standard text used by many instrumentation courses. However, I found the information out of date. There is also insufficient amount of examples and end-of-chapter problems.