Scotopic

A team of research scientists at the Lawrence Berkeley National Laboratory (LBNL), headed by Dr. Sam Berman, Ph.D., has scientifically shown that light enhanced in the blue-green portion of visible light is superior to regular white light. Scotopic peak response is found at 507 nanometers (nm).

Enhancing the blue-green spectrum of light is referred to as scotopically enhanced light. This is most important to understand, because visual performance is generally improved with smaller pupil size. This is even true for light levels typical of building interiors. This led the LBNL team to propose that reducing pupil size via shifting lamp color of light toward higher scotopic (blue-green) content could compensate for any reduction in visual performance caused by reducing light levels. Reduced light levels lead to substantial energy savings without compromising visual performance.

Scotopic Response

In the drawing on the left, some light rays are absorbed by the iris, which lies in front of the lens. The rays that pass through the lens are scattered along the retinal surface. The rays of light that land on the macula become focusable, while all other rays remain blurred or become peripheral images (confusing rays). The drawing on the right demonstrates how the iris eliminates the confusing rays of light. When the pupil is smaller, the iris absorbs more of the light. This action allows less confusing light rays back to the retinal surface. When the pupil is smaller, the depth of field increases and visual acuity improves. This occurs even though the total amount of illumination received by the retina has decreased.

Please take the time to read Dr. Sam Berman's report that was presented at the 1991 IESNA Annual Conference entitled: "Energy Efficiency Consequences of Scotopic Sensitivity." The report explains the energy saving aspects and cost efficiency of scotopically enhanced lighting.

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