How do television/LCD screens make the color black?

Question

Is it black light, the absence of color, or an optical strategy using multiple colors? Is it possible to create a black light?

Answer 1

I am not sure what length of answer you are looking for, so I will give you some short and long answers

Short answer: You can't have black light. As you mentioned, black is literally the absence of light. Ideally, your monitor or LCD "makes" black by not lighting up the pixels, just like your printer "makes" white by not spitting any ink on the page

Long answer: Creating a black light: You might want to check out a wikipedia article on Color Theory ( http://en.wikipedia.org/wiki/Color_theory ). If you put certain colors together, they actually "cancel" each other out, and appear darker. ANY WAVE, be it microwave, radio, light, or sound, can be CANCELED out by another wave in the opposite phase.
Anti-noise is a good example of wave canceling, and you can find Noise Canceling Headphones that apply this concept. This can be done, theoretically, in the same way with light.
Let's say for argument's sake your LCD is smart. And there's a glare of yellowish light coming through the window, and it's bouncing off making a glare. Your eye will look at the pixel and "see" a yellowish color, which you don't want. Now, since your LCD is smart, it detects a yellowish light in a positive phase, so it "lights" the pixel with the same yellowish light in the negative phase. By the time the light hits your eye, the positive and the negative light will have canceled each other out, so you will see Black. Since there was an existing yellowish color from the window, and the LCD made it look black, it "made" a black light.
Now, unfortunately, there is no LCD that is NEARLY that smart, and probably won't be for a long time. However, in that sense, it is possible to make a "black light" by putting out the same type of light you see, but in a different phase, which kills the light and "creates" black. Other than that, black really is just the absence of light.

Answer 2

Early LCDs had a fixed backlight that was always on at a fixed value, so to create black you had to combine red green and blue. In other words, in current LCDs it is impossible to turn off the backlight in some part of the picture and have it on in another. However, LCDs do have the capability to dim the back light intensity, and hence improve black colors in dark scenes.

As the backlight source switches from fluorescent to LEDs it will be possible to turn the light off at specific areas of the picture, which will create even better blacks.