##How Light Works
Visible light has a wavelength in the range of about 380 nanometres (nm), or 380×10−9 m, to about 740 nanometres.   Every color that we see corresponds to a different wavelength, from the very long  (red to orange - 600-700nm) to short (violet to ultraviolet - 440-360 nm).   Beyond that, you have the rest of the electromagnetic spectrum, stretching in each direction as far as the eye can see -- or can't see, as the case may be.   Visible light makes up a very small portion of the electromagnetic spectrum. 

[![EM_spectrum.svg.png](https://i.publiclab.org/system/images/photos/000/001/741/medium/EM_spectrum.svg.png)](https://i.publiclab.org/system/images/photos/000/001/741/original/EM_spectrum.svg.png)
(courtesy of [wikipedia](http://en.wikipedia.org/wiki/Light))

All of the light we perceive falls within that tiny range.    One thing that's interesting here:  you'll notice that white light doesn't show up on the image above.  That's because white light isn't actually a color - it's all the colors mixed together  (or rather, they appear to be mixed, because full spectrum light activates all three types of cone cells in your eye - red green and blue).   It's called [additive mixing](http://en.wikipedia.org/wiki/Additive_mixing).   Consequently, when you see white light, you are actually seeing the full color spectrum. 

Here is a picture of a pretty standard form of visible light -- the sun!

[![THE_SUN.jpg](https://i.publiclab.org/system/images/photos/000/001/739/medium/THE_SUN.jpg)](https://i.publiclab.org/system/images/photos/000/001/739/original/THE_SUN.jpg)

If you take a prism and scatter the light from the sun, you can see the individual colors that make up white light.   You can actually use a second prism to reassemble the spectrum i.e. turn it back into white light.   Alternatively, you can look at the spectrum to get a much more precise idea of what wavelengths are present in your light source.  

[![prism.png](https://i.publiclab.org/system/images/photos/000/001/745/medium/prism.png)](https://i.publiclab.org/system/images/photos/000/001/745/original/prism.png)
(courtesy of [fdecomite](https://www.flickr.com/photos/fdecomite/8530626099/))

##Different kinds of white light

Incandescent
[![incandescent.png](https://i.publiclab.org/system/images/photos/000/001/758/medium/incandescent.png)](https://i.publiclab.org/system/images/photos/000/001/758/original/incandescent.png)

Fluorescent
[![fluorescent.jpg](https://i.publiclab.org/system/images/photos/000/001/759/medium/fluorescent.jpg)](https://i.publiclab.org/system/images/photos/000/001/759/original/fluorescent.jpg)

White LED
[![white_led.png](https://i.publiclab.org/system/images/photos/000/001/760/medium/white_led.png)](https://i.publiclab.org/system/images/photos/000/001/760/original/white_led.png)

Sunlight
[![sunlight_spectrum.png](https://i.publiclab.org/system/images/photos/000/001/756/medium/sunlight_spectrum.png)](https://i.publiclab.org/system/images/photos/000/001/756/original/sunlight_spectrum.png)