Digital Prints

154
Mastering Digital Printing
What Are Normal Display Conditions, and How Are They Measured?
What’s normal? It depends on where you are and whom you ask. According to independent researcher Barbara Vogt, the average amount of light
an image is exposed to in U.S. homes is about 215 lux (lux is an illumination measurement) with the temperature and humidity at an average of
21° C and 50% RH (relative humidity). The Eastman Kodak Company says that 120 lux (with 23° C and 50% RH) is a good, overall estimate
for “typical home display.” Henry Wilhelm has adopted 450 lux for 12 hours per day (24° C and 60% RH) to simulate “standard,” indoor display
conditions. Photographer Stephen Livick along with fade researcher Bill Waterson have settled on 275 lux as “average home daylight lux display
level.” The Montreal Museum of Fine Arts uses 75 lux and 100 lux illumination levels for its exhibits, which it rotates between display and dark
storage. David Matz has measured the light levels in his house. One wall (with art) in his living room gets three hours of sunlight each day at an
intensity of 50,000 lux; when the sunlight leaves, the room lighting drops to under 2,000 lux.
Conclusion? There are no normal display conditions! In fact, there isn’t even agreement that lux should be the measurement used. While the photographic
world promotes lux since it’s based on the human eye’s response to light, prints are also affected to a significant degree by the shorter
wavelengths (320–400 nm) that typically go undetected when using lux as the metric.
Are there other options? ASTM International and researchers like Q-Panel’s Eric Everett recommend watts per square meter (W/m2) for the irradiance
level and joules per square meter (J/m2) for the total radiant exposure. And how are these measurements taken? Unfortunately, only with
expensive radiometers or testing devices equipped for it.
The foyer in this house is lit by a
combination of diffused, indirect
window light and overhead
incandescent spotlights. The midday
illumination level at the sailboat
painting is around 200 lux.