In an effort to get around the problem of the eye’s iris being wide open, ambient light is added to the environment. The eye’s iris is biased by the ambient light. It is closed down a little, from the original wide open position, and better able to handle the very bright picture transitions. If the bias light is set properly, the eye still has enough dynamic range to allow the person to see into the dark areas of the picture. The need for a bias light has been clearly established as a result of several years worth of human factors research. Introducing this light introduces an environment to the monitor, which will influence the color perception of the picture coming from the monitor. The conditions of this “bias light” become very important.
What are the major considerations of introducing this light? There are some obvious points. The light needs to be in the environment of the display device. It shouldn’t be positioned where it canshine directly on the display or the viewer or be reflected back to the viewer by the display. Ideally, that means that the light should be behind the display aimed in the opposite direction of the viewer. The conditions perceived by the viewer of the light/environment combination are very important.
Knowing that a person’s perception of color is dependent on the environment, is it possible to specify a single environment that will assist in properly determining the color spectrum capability of the television system? Yes, just as the “color” of gray on the monitor itself will effect all the other colors, it turns out that a neutral surround, gray; which contains all colors, is the right choice for the environment. Ideally, the gray in the environment has to match the properly calibrated gray of the monitor.
What about intensity of the light? The SMPTE Recommended Practice document says the level should be less than 10% of the peak white level on the viewing device. How much less? Most viewers in the professional world settle in at around 5%.
Be prepared! The initial reaction of most interior decorators is going to be “off the wall” when this information is first presented. In the past they have managed to destroy proper perception of color in the process of creating a “warm, friendly” environment. There are times when the viewer would like to see the information the system is trying to present. The warm, friendly colors in the environment are not warm and friendly to proper color perception.
With a little creativity, gray does not equate to “drab”. The background grays should have shades, relief, texture, and/or design. There is a great deal of room for individual expression within two basic parameters; the maximum level of light coming from any point in the background should be no more than 10% of the peak white level of the display device, (measured in the plane of the display device), and the background color should be neutral, the same color of gray as the gray scale of the properly calibrated monitor.
For more information about a D65 bias lighting solution, please visit www.biaslighting.com