VISIBLE LIGHT - Some Details

The shortest wavelength (highest frequency) light our eyes can sense has meters.

Our BRAIN interprets this as BLUE/VIOLET light.

Move to longer wavelengths and we see Green, Yellow, Orange, Red.


If a light source produces all the colors from red through blue, our brain interprets this as white light

It is easy to demonstrate this (white light contains all the colors) by ``dispersing'' the light.

1. Prism

   

2. raindrop

3. magic crystals obtainable from 3/4 of the stores on Pacific Avenue.
• The usual colors we see are due to the reflective properties of objects. This fact can also be used to demonstrate that white light contains all the colors of the rainbow.

• We have white light sources in the room. The color of all the objects in the room aside from the lights is determined by the wavelengths of light that the objects reflect.

• BLACK shirt absorbs all visible wavelengths (that is why black clothes are warmer).

• RED shirt absorbs all the wavelengths except for RED (so, the white lights must be emitting some Red light).

• BLUE shirt absorbs all the wavelengths except for BLUE (so the white lights must be emitting some Blue light).

Q. What wavelengths are reflected by a White shirt?

Q. What color is a Yellow banana illuminated with Red light?

E-M radiation and the atmosphere

• The atmosphere only passes certain ``spectral windows'' (either way).

• The atmosphere is transparent to visible light (why do you think our eyes evolved to be sensitive to these wavelengths?), some parts of the radio spectrum, and some parts of the Infrared.

  Fortunately, UV, X-ray and Gamma ray radiation does not reach the surface of the Earth as they all cause various bad things to happen to humans, other animals and plants. This also means if we want to make observations of X-rays from the Universe we need to launch X-ray observatories into space.