# Qn on light

1. Jan 6, 2005

### gunblaze

How is White light form?

I know that it is a combination of 7 colours...But just want to know how the 7 light with different frequencies merged?

2. Jan 6, 2005

### Integral

Staff Emeritus
Actually visible light is composed of much more then 7 colors. The visible spectrum is composed of any frequency in the range 400nm to 700nm. This region was arbitrarily subdivide into 7 colors by Newton. It is said that his believe in numerology dictated the 7. If you look at a rainbow there are only 6 easily identifiable colors. Notice when look at a rainbow that the division between the colors is not sharp, one color bleeds into the next this is an indication that there are a great many different frequencies combining to create the colors we see. Do a wiki search on Superposition principle to learn more about how the different waves combine.

3. Jan 6, 2005

### Galileo

Still, you can divide the visible spectrum into thirds.
On the left end (largest wavelength) is red, in the middle is green and on the other end is blue.
Red, green and blue are considered the primary colors of the visible spectrum.
If you add these colors with equal intensity you will have white light.
You can also get every other color in the visible spectrum by combining (or adding by superposition) these three colors with varying intensities.