Luminance¸ or Luma

Brightness of a light emitting object, or the portion of a video signal that represents brightness. Used by itself, the luminance signal is sufficient to produce a full black and white image. It is said that the luminance signal is responsible for the picture detail. This is true because as the video standards (NTSC, etc.) were defined, the luminance signal was given a larger bandwidth to permit the carrying of all of the picture detail while the color signal was deliberately constrained to consume less bandwidth and consequently possess less detail. Those readers who know the difference between "luminance" and "luma" should refer to Prime Disclaimer.