It would take a while to fully explain. I also don't know all of it. I reccomend looking at the wiki pages for PHOT and also FILT, though the FILT page would be less helpful.

As Jakav said, explore the wiki. Namely PHOT and FILT, but ARAY, BRAY, and LDTC may also help if you plan on doing more things.

I made a simple contraption that should help you understand it better:

Explanation:

It shoots out a line of photons, with two wavelengths (26 and 260,000,000, or blue and yellow). A receiver device uses LDTC to capture the wavelength and send it to a strip of FILT. A permanent (subframe) BRAY is shot through the FILT and then through another FILT strip which has the 26 * 10^7 wavelength. This piece of FILT has tmp 1 (bitwise AND) and only passes through BRAY that matches its own wavelengths. If the BRAY passes, it sparks a conductor, flashing a LCRY light. 

You're welcome! Glad I could help.

(Meanwhile, I'm working on a radio station thing that broadcasts messages using this method)