Multiple Modes of Vision

- Sep 04, 2019-

These sensitive light-translating cells at the back of your eye come in two primary distinctions; rods and cones. There are roughly 7 million cone cells in each eye, primarily responsible for receiving and interpreting the subtle differences between color and sharpness. These cones are a mix of red, green, and blue. In well-lit environments, our vision relies primarily on these cones, a mode we call photopic.

Conversely, when the lighting conditions are extremely low, like at night or in a dark room, human vision shifts from this photopic, cone-based mode to a scotopic mode, which relies on the 120 million rods that dominate the eye’s receptor cells. These rods are thousands of times more light-sensitive than their cone counterparts, however they only respond to white light. The scotopic, rod-based mode of vision is ideal for night vision and aids in detecting movement and peripheral vision.

During the low-light conditions in between these two extremes, the eye utilizes a varying combination of both rods and cones. This mode is called mesopic vision and relies on the adjustment of brightness from one mode to the other, often more prominently expressed under moonlight and indoor lighting.

Traditional approaches to the design of lighting in office and industrial environments has been heavily focused on photopic vision in relation to brightness, which preferences the eye’s cones over the rods. This design approach assumes that increasing light levels overall will improve visual sharpness and acuity, however it also correlates directly with energy use.

Modern advances in lighting design for corporate and commercial spaces are beginning to take scotopic and mesopic visionary modes into account so as to incorporate the highly-specialized rod cells of the eye. Research by the U.S. Energy Department suggests that a more comprehensive approach to lighting design, which takes into account a well-balanced mix of light to suit all three modes of vision, demonstrates marked improvements in the quality of light perception for those working in these spaces. Since rods primarily control the opening and closing of the pupil, scotopically enhanced lighting schemes are overwhelmingly preferable to those that do not account for scotopic vision. Of course, these more nuanced lighting displays burn less energy to achieve the added sharpness and deeper perception.