White LED Light Source Technology for High-Speed Scanning
To enhance the productivity in offices, multifunction devices (MFDs) have recently been required to read documents faster while consuming less energy. However, increasing the reading speed with a xenon lamp-the light source used for scanners in existing MFDs-poses a problem because higher speed requires higher illuminance, which would result in a large increase in energy consumption.
To solve this problem, Fuji Xerox has adopted white LEDs as the light source for such scanners and successfully increased brightness by 1.5 times, while reducing the energy consumed by this lighting by 70%.
Energy Efficiency of White LEDs
These white LEDs are extremely energy efficient, realizing light 1.5 times brighter than that of a xenon lamp at about one-third the energy consumption. Using these LEDs as the light source for a scanner enables energy-saving, high-speed scanning. Given the good responsiveness to On/Off switching and quickly stabilized illuminance of these LEDs, we were able to shorten the recovery time from energy-saving mode, thereby achieving both energy efficiency and user friendliness.
|Item||Xenon lamp||LED||LED compared to xenon lamp|
|Illuminance of document surface (lx)||14,000||22,000||× 1.5|
|Power (W)||12||3.5||Reduced 70% (1/3 or less)|
|ON/OFF responsiveness (sec)||1 × 10-1 - 10-2||1 × 10-4 - 10-5||1/1,000|
|Energy efficiency(lx / W)||1,170||6,290||× 5.4|
Technology Enabling LED Use in Scanners
LEDs are a point source light and the brightness of each LED is slightly different. An array of LEDs therefore creates nonuniform brightness, resulting in very poor image quality. To address this problem, we developed an original optical component that combines a light guiding device (waveguide) and a special diffuser panel to achieve a distribution of uniform brightness equivalent to that of the xenon lamp in the illuminated area.
The chromaticity distribution of the white LED is more than four times wider than that of the xenon lamp. This causes the emission color to vary, and image quality of the color MFD cannot be maintained or stabilized. Fuji Xerox has overcome this problem by developing a new technology for digitally correcting the color component automatically per machine using an original image processing algorithm, and enabled the effective stabilization of image quality of a level equivalent to that provided by the xenon lamp.