Lighting Research Center Lighting Research Center

Applying Research on Night Vision

Perception of Color, Brightness, and Clarity

We compared visual performance under high pressure sodium (HPS) and metal halide (MH) lamps to extend the LRC's basic research on nighttime (mesopic) visual function into the areas of perception of color, brightness, and clarity.

This study indicates that MH lamps are superior to HPS lamps for nighttime applications where off-axis visual tasks are performed.

Reaction Time: At three typical nighttime luminances (1 cd/m 2, 0.1 cd/m 2 and 0.01 cd/m 2), reaction times to small, flashed, off-axis targets were significantly less under MH lamps than under HPS lamps for equal luminances. This difference was greatest at the lowest mesopic levels. Reaction times to on-axis targets were equal for both sources at equal luminances.

Color Identification: Subjects always identified color more accurately under MH lamps than under HPS.

Pupil Size: For the luminances tested, the pupil was large and independent of light source.
Monocular pupil size as a function of adaptation luminance. Below 1 cd/m 2, there is no significant difference in pupil size between HPS and MH lighting.

Haziness-clarity Rating: A diorama seen under MH was rated slightly clearer than when seen under HPS at the same luminance.
Figure 2a. View of diorama, looking into test apparatus.

Figure 2b. Diorama as viewed from above.

Brightness Matching: Subjective levels of brightness were 50% to 100% greater for MH than for HPS at the same luminance.

Sponsor: U.S. Army

Rensselaer Polytechnic Institute
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