For practical purposes this luminous intensity per unit area is called photometric brightness or luminance of a material and is measured in lambert or millilambert (0.001 lambert) units (one lambert is equal to one candle per square centimetre divided by π).
The monochrome displays of the day suffered from terrible flicker, high contrast and fluctuating luminance.
At the same time, the array of three values simplifies the complexity in the image, so even if a video is of poor quality or a different hue, the information about its relative luminance is retained.
The first phosphor synthesized was probably an impure barium sulfide preparation with very low luminance efficiency and with the serious shortcoming that it was rather quickly decomposed in moist air, yielding hydrogen sulfide.
The ratio of the candle power of a source to its area is called the luminance of the source; luminances range from about 2,000 candles per square millimetre at the surface of the Sun down to about 3 × 10−6 candle per square centimetre (3 × 10−6 stilb) for the luminous paint on a watch dial.
Ordinary outdoor scenes in daylight have an average luminance of several hundred candles per square foot.
The area of the image is Am2, in which m, the magnification, is given by Hence, the image illuminance (E) is The image illuminance thus depends only on the luminance of the source and the cone angle of the beam proceeding from the lens to the image.
To obtain a film image that faithfully records all the tone gradation of the object, this exposure must be matched to the brightness (luminance) of the subject and to the sensitivity or speed of the film.
