HP Color LaserJet 8500 Service Manual - Page 441

Understanding color variations The printed output might not match the computer screen, and the colors printed on successive pages might not match. While color variations are inherent in this printing method, they also might indicate changes in the printing environment, print media, or printer components. Common causes of color variation The following list outlines the major causes of color variations between computers, applications, and output devices.
Half-tone patterns produced on monitors and the types of patterns used in the print jobs are different and might cause apparent differences between the printed output and the screen.
Different papers have different color, brightness, and gloss, which will affect the color appearance.
Printed colors with identical CMYK or RGB values but with a different halftone (ColorSmart, text, graphic, or image) might look different when printed. Select the manual color option in the driver and change the halftoning options to vary the shading and quality of the colors.
The printed output differs from the image on the monitor because the monitor and the print media have different reference values for black and white. The monitor screen has charcoal gray for the black level, and the white on the monitor screen is actually a light blue. Black on the print media is limited only by the fill capability of the printer, and most good-quality paper has a very high white level. In addition, phosphor (used in color monitors) and toner have entirely different spectra characteristics and different color rendering capabilities. Blues generally match better than reds.
The color of the ambient light changes the perception of color. Fluorescent light emphasizes different colors from incandescent light, and the color range of natural light is broader than any artificial light. When comparing color, choose a standard light source for reference and understand that the perceived color will change as the light changes.
Long-term color variations occur as the paper ages. Use high- quality paper and protect the paper from sunlight to help minimize discoloration.
Environmental changes can cause color variation. The development process places a high potential across an air gap to attract toner to the imaging drum. Changes in relative humidity vary the point at which the toner travels to the imaging drum. The EN Image formation troubleshooting 439