Light can be classified into two categories: AC light and DC light. AC light varies in intensity and color makeup as a function of time. DC light has uniform intensity and color makeup over time. AC lighting historically has been very bad in any type of machine vision applications, due to varying light intensity and color between frames. This is due to the fact that cameras typically shutter more rapidly than one full period of an AC light waveform. DC lighting has none of these issues.
An additional technique used in Tele-Collaboration projects, known as Imperceptible Structured Light(ISL), also has problems which Digital light can help to solve. ISL applications require that a pattern be projected that cannot be seen by the human eye, but that can be picked up by a camera. Currently, the room must be very dark to demonstrate this, so that ambient light does not wash out the projected imperceptible structured light.
The Solution: Digital Light
Digital Light is a viable solution to the aforementioned problems. Digital Light consist of DC light sources under strict timing control. DC light sources are used in order to eliminate the problems which exist with AC lighting, such a differing color and intensity values for the same point in space over time. The timing control aspect addresses the problem of providing the cameras with enough light without washing out the image on the projection screen. This is achieved by keeping the DC light sources at a low level, and pulsing them at the exact instant when the cameras shutter. This pulsing occurs well outside the range of human perception. This allows humans to perceive a very low level of light in the room, and view a high quality image on the projection screen, while at the same time providing the camera with the necessary room illumination level to generate high quality images. The ISL problem will be solved, by using LEDs to illuminate the entire room. The the LEDs will be turned off during the camera shutter and on at all other times. This will allow the room to be dark to the camera, but provide the humans in the room with normal ambient lighting