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Contrast, Glare, Blobs, and Smears

Light That Helps Us See and Feel Better

“Vision is about information,” says lighting designer and scientist Naomi Miller. “Lighting can hinder or help the brain’s ability to process information.” A large part of processing and understanding visual information comes from seeing contrast. It is what enables people to comprehend their surroundings.

Contrast is how we identify edges and boundaries. It’s why we see dark print on white paper and patterns,” explains Landscape Forms. “But glare and overlighting can prevent us from seeing contrast as needed, and, therefore, our visual performance is reduced.”

As light levels get lower, the visual system shifts. The cones in our eyes, which detect details in color, grow less sensitive, and the rods, which see only in black, white, and shades of gray, begin to dominate in processing information. Rods are highly sensitive and pick up contrast at low light levels, especially in peripheral vision. “While we see limited color in very low light, we still can see contrast,” explains Miller. “I may not be able to tell the color of the bedspread if I wake in the middle of the night, but I can see the contrast of it against the backdrop of the room. What is important is having enough information to still see an edge. Our visual system is designed to be an edge detector. We’re good at picking up the edge of a road, the hood of a car, the outline of a building. Contrast is what lets us see that edge.”

Because our vision changes as we adapt to lower light levels, overlighting reduces the eye’s ability to see well. The glare of a high-intensity light can impede vision, for example. “We can pack a lot of lumens into a teeny tiny LED, and it’s blindingly bright,” says Miller. “But just because the technology allows us to do that doesn’t mean we should. Lighting that helps people see and feel better is about quality, not quantity, and more about uniform light distribution at appropriate light levels.”

There are two types of glare: discomfort glare and disability glare; one introduces discomfort and the other inhibits the ability to see clearly. However, light quantity doesn’t solely define glare. Shining a light in someone’s eyes at night will have a different effect than shining a light in someone’s eyes on a bright afternoon. The glare response has to do with current vision adaptation levels.

Discomfort glare doesn’t affect vision but makes you want to look away from the light. You may put your hand up to shield your eyes from a bright light in a parking lot, but you can still see. Disability glare reduces contrast and your ability to see. Bright headlights coming at you as you drive create scatter in the eye and a smear of light on the retina that washes out the retinal image. The result: Your ability to see the roadway ahead is hindered.

"It’s a matter of putting the light where you need it and, just as important, not putting it where you don’t,” says Miller. “More important than lighting brightly is to light uniformly. Avoid dark patch, bright patch, dark patch, bright patch patterns. The visual system shifts up to see details under bright light levels, and it becomes more difficult to shift the system back down to see in lower light levels. Gradual transitions allow people to see more clearly in both bright and dimmer areas, and more uniform light makes it easier to see.”

"We need to move light into useful zones, not into people’s eyes, which translates to glare,” continues Miller. “Light the sidewalk, roadway, or building but do so in a controlled way so there isn’t glare. We need just the right amount of diffusion to reduce glare but not so much to affect light distribution. This avoids a blob that sends out horizontal light and defeats the point of delivering light where you need it. Avoid light trespass. Avoid lighting animal habitats at night. Think about both environmental and human needs. Uplighting interferes with our ability to see the night sky and negatively impacts birds and nocturnal animals because it contributes to skyglow.”

If you’re a specifier and care about human comfort, think about a lighting product that has enough optics in it to avoid hard-edged LEDs but at the same time has a sculptural light distribution that puts light where it is needed. It’s about balancing visual comfort and light distribution,” says Miller.

Miller is a member of the Illuminating Engineering Society’s (IES) Quality Lighting for People in Outdoor Spaces Committee. The committee was charged with creating pedestrian-oriented lighting recommendations for outdoor spaces, which ultimately led to a hierarchy of the things people need from outdoor space. “The hierarchy presents an appropriate way to approach an outdoor lighting problem,” says Miller. Rick explains: “You need to orient, navigate, and be reassured that you’re safe, that you know where you’re going. If people don’t feel comfortable or safe, they won’t engage with the outdoor space. Finally, people may search for specific atmospheres and enjoyment. People can’t enjoy an outdoor space if they don’t feel oriented, reassured, and safe first.”

To encourage people to enjoy the outdoors at night, we want lighting that makes people, buildings, and landscapes look pleasant,” says Miller. “That’s why color quality is so important, even at low light levels. Many people prefer to see warmer colors at night. This may be part of our evolution from fire and moonlight as our nighttime light sources. Under warm-color white LEDs, you can you can see faces, colors, and patterns. Your brain is getting the information it needs to see.”

Naomi Miller is a lighting designer, researcher, author, and scientist. She has worked as an applications engineer and lighting designer with decades of experience in design and installations and taught at Rensselaer Polytechnic Institute’s Lighting Research Center. For the past 10 years as a Senior Lighting Engineer at the Pacific Northwest National Laboratory, a Department of Energy National Laboratory, Miller has worked to make LED products better, educate users and specifiers about them, and speed the adoption of high-quality, energy-efficient architectural lighting.


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