An Evaluation of Office Light Sources for Assessment of Printed Material

Abstract

This study examines the lighting conditions, specifically the light source, when assessing printed material at offices. It assumes that the straight-tube type of fluorescent lamp is used as the light source in most offices. The total of 86 commercially available fluorescent lamps, including general, high color rendering(EDL and SDL), and narrow-band(EX)types, were tested. Using CIECAM02, the colors of printed material viewed under a fluorescent lamp were converted into corresponding colors under the standard illuminant, D₅₀ . The difference between colors under the standard illuminant and these corresponding colors was evaluated according to the acceptable tolerance derived from criterion set by experts in the printing industry. The Japan Color was adopted as a representative of typical offset printing. EDL lamps with natural white color or with the daylight color were evaluated as acceptable in accordance with the tolerance. The secondary level of tolerance, Level-II, was derived from criterion established by common observers. This level is applied for general assessments of printing in which critical judgment is not required. All of the SDL lamps tested were evaluated within Level-II, as were EX lamps with natural white color. Proofs printed using DDCPs were also used as a subject for the assessments. Again, EDL lamps with natural white color or with the daylight color were evaluated as Level-I. All SDL lamps were evaluated as Level-II, as were EX lamps with natural white color and R_a above 88. In conclusion, an EDL lamp with natural white color is required when critical assessment has to be performed. Alternatively, an EDL lamp with daylight color may be used for the assessment. For general day-to-day assessments, which doesn't require as strict assessment decision, an EX lamp with natural white color and R_a above 88 can be used.