Color blindness affects perception of LED signals
by Rachel Guan, Mn/DOT
Does color blindness affect the perception of green light-emitting diode (LED) signal indications? As the use of LED signals becomes more popular, new issues have emerged that need investigation to determine the impact this new technology has on the driving public.
In the fall of 2002, the Minnesota Department of Transportation (Mn/DOT) received a complaint from a color-blind citizen concerning his ability to properly perceive the new LED indications. Under direct sunlight conditions, especially near the spring and fall equinox, the color-blind individual could not determine which indication, either red or green, was illuminated.
Color blindness, also known as color-vision deficiency, affects up to 8 percent of the male population and 0.5 percent of the female population in the United States. Normal color vision requires the use of specialized receptor cells called cones, which are located in the retina of the eye. There are three types of cones—red, blue, and green—that enable people to see a wide spectrum of colors. Color blindness occurs when the amount of pigment sensitivity per cone is reduced, or when one or more of the three cone systems is absent.
There are two main forms of color blindness. Red/green color blindness (deuteranopia) is the most common deficiency, along with blue color blindness (protanopia), which is an inability to distinguish both blue and yellow (they are seen as white or gray). The following photos illustrate the color-deficient traveler perceptions of traffic signal indications.
Radio Drive & Hudson Road: Protanope
Radio Drive & Hudson Road: Deuteranope
Radio Drive & Hudson Road: Normal
Valley Creek Road at Radio Drive: Protanope
Valley Creek Road at Radio Drive: Deuteranope
Valley Creek Road at Radio Drive: Normal
Valley Creek Road at Queens Drive: Protanope
Valley Creek Road at Queens Drive: Deuteranope
Valley Creek Road at Queens Drive: Normal
Color vision deficiency affects a significant number of motorists. In 2002 and 2003, Mn/DOT teamed with Washington County and conducted a green LED preliminary investigation and field-testing study.
The study involved the purchase of a number of different LED signal indications from multiple manufacturers. The different LED indications varied in their design, with a main variation being the color of the lens or housing of the LED. Some models came with a clear lens and others had a green-tinted lens.
The preliminary investigation found that the clear lens green LED reflection could appear brighter under direct lighting conditions. To further investigate the impacts, different designs of LED signal heads were installed on Valley Creek Road in Washington County, and a field-testing study was conducted by the team. Field testing was conducted from April 8 through April 10, 2003. Both color-blind and non-color-blind subjects were driven through the test intersections, and interviews were conducted at each intersection. The study determined that:
- There is a difference in green LED perceptions between color-blind and non-color-blind people.
- There are different impacts on perceptions from different signal indication designs. The green-tinted lens was better for the color-blind, but the clear lens was better for the non-color-blind.
- The best solutions are very different for color-blind versus non-color-blind travelers. The brand and the design of the head (high LED count versus low LED count) that was best was different for color-blind versus non-color-blind.
The project recommended that more study would be needed to determine whether any of the designs currently on the market can balance the needs of color-blind and non-color-blind drivers.
The study results were published in the August 2004 issue of the ITE Journal. For more information on the field study, please contact Ray Starr, Mn/DOT, ray.starr@dot.state.mn.us; Wayne Sandberg, Washington County, wayne.sandberg@co.washington .mn.us; or Rachel Guan, Mn/DOT, Rachel.guan@dot.state.mn.us.