At high light output, a display will typically start to bloom in the bright white areas of the picture and over-saturate the colors. The lower the light output, the sharper the image will be. At lower light output levels, you want as little ambient light as possible competing with your display. No display, whether field calibrated or not, can produce a good picture with direct sunlight hitting the face of the display or with glare from a window or bright objects in the room. Yet, no manufacturer advertises that you will need to tightly control the ambient light level to get the best picture on their display. Room accent lighting is acceptable, if properly directed within your room. Consider directional lighting, recessed ceiling lights, and sconces.
Backlighting
For an ideal viewing environment with a smaller display, there should be some light in the room. Watching a direct-view display in a totally dark room strains and fatigues your eyes, because at recommended viewing distances the screen occupies only about 20 degrees of your field of view. The large dark area surrounding the display causes the iris of your eye to open wide. This causes the bright screen image to overload the small lighted portion of your optic nerve.
A small amount of light in the room helps minimize eye fatigue and contributes to a more enjoyable viewing experience. The light source should be dim and be placed in such a way as to minimize glare and reflections on the screen. Usually the best way to accomplish this is to place the light source behind the display. The backlight then produces a dim glow around the display, minimizing the difference between the bright display and the dark surround.
Because of the way our eyes take surrounding light into account when interpreting colors, the backlight should be close to the display's reference white color, D65, which has a color temperature of 6500 Kelvin. A 15 watt fluorescent fixture, containing a bulb with a color temperature of 6500 Kelvin and at least a 90 CRI (Color Rendering Index) works very well. The high CRI means that the light output spectrum will be close to that of sunlight and won't make some objects turn "funny" colors.
Backlighting is usually not required with rear projections TVs and front projection screens. Since the screen is large and the display resolution is high enough that we can't see individual scan lines, the recommended viewing distance usually causes the screen to occupy at least 30 degrees of our field of view. The display image then lights a large enough area of the optic nerve to properly control the eye's iris, for no viewing fatigue.
Back to Video Calibration Details