Measuring the Color of Light

Ever wondered what the heck 6500 Kelvin has to do with your photos? Here’s an in-depth article from the blog of James Duncan Davidson for better understanding of the whole color and white balance thing in photography.

Measuring the Color of Light by James Duncan Davidson:

Like all settings, the color of light has a unit associated with it. The unit, however, isn’t unique to specifying the color of light. Instead, it’s the same SI unit that is used for temperature: the Kelvin. I know that the first few times I delved into this subject matter, I thought it was a strange unit to use, mostly because light itself doesn’t have a temperature. Since it’s radiation, when it hits a surface it can cause that surface to heat up. But the light itself is neither hot nor cold. So, why the heck is a unit of temperature used to describe the color of it? …

And another in-depth article from James which is a follow up of the above article:
Color Temperature and White Balance