The two kinds of receptor in the eye are rods and cones. Rods only see in black and white but are very light sensitive (that's why you see in black and white when it is almost dark) and cones which allow you to see in colour.
Light (electromagnetic radiation) forms a continuous spectrum there are no two main types.
Natural Light (sunlight) and Artificial Light (flashes/studio lights)
Alpha and Beta
sun :) lightbulb. NOT THE MOON!
Photo receptors and signal receptors.