Modelling
Physics 101 - Light
Electromagnetic radiation is energy travelling in either waves or phothons (this is not the place or the time to go into this descssion*.) but Einstein said it well: "But what is light really? Is it a wave or a shower of photons? There seems no likelihood for forming a consistent description of the phenomena of light by a choice of only one of the two languages. It seems as though we must use sometimes the one theory and sometimes the other, while at times we may use either. We are faced with a new kind of difficulty. We have two contradictory pictures of reality; separately neither of them fully explains the phenomena of light, but together they do." -- Albert Einstein and Leopold Infeld, The Evolution of Physics, pg. 262-263. Light, or the visible light spectrum range from $\approx 400 - 700$nm in the electromagnetic radiation spectrum (insert en ref to picture of the spectrum). Above, with higher wavelengths, you will find infrared radiation (also known as IR), and under you will find the ultraviolet radiation (also known as UV).
Physics 101 - LED
Not monochromatic, circuite explanation
Physics 101 - Wavelength
The given wavelength $\lambda$ for a lightsource can be found by XX INSERT FORMULA HERE XX, by knowing the grid spacing, $d$ and angle, $\theta$.
Physics 101 - (Bio)laser
Mirrors, filters
* if you want to read more about the waves vs. photons disussion: https://en.wikipedia.org/wiki/Wave%E2%80%93particle_duality