When you look at the television, the colors look natural. Sometimes the screen is predominantly green or yellow or red or blue, depending on the situation. But if you watch a window illuminated by a television set at night, the light shining out always looks blue. Why is that?


Color temperature is a term that a lot of videographers and photographers are very familiar with. It's the overall color of combined wavelengths of light from a light source. For example, blending red light and green light will give you yellow light. Why is temperature involved? To make things a little more confusing, of course! "Color temperature" refers to the temperature in degrees Kelven to which you'd have to heat an ideal source of light radiation in order to get that color. Low temperatures - in the two and three thousand kelvin range - are called warm colors, because they're yellow and red. High temperatures of upwards of five thousand are called cool colors because they are in the blue and white range.

As you go down a dark street at light, you won't just see televisions lighting up windows and making them blue. You'll also see a light bulbs lighting up windows to make them yellow. Have you ever noticed those light bulbs making every room you enter at night a deep shade of yellow? No, of course not. Your eyes adjust and see it as more white. Light bulbs are about 3200 K, and so are yellow when looked at briefly from someone who has other things to compare them to. TVs, on the other hand, give off shades of red, green, and blue which combine to have a color temperature in the 5500 to 6500 K range. That'll make them look bluish for someone walking on the street and comparing them to yellow streetlights and yellow house lights. It will also make them blue if someone is sitting in a room illuminated by a light bulb and looking at a room illuminated by a television.


Incidentally, tv light isn't the only thing that turns blue. Many people have seen an electric-blue evening sky from their lit window only to be disappointed at its dimness and unremarkable color when they turn off the light or go outside. They didn't miss that bright blue evening light, they created it, in their minds, by comparing to the light in their house.

Via CQ and Physics Classroom.