Not all lighting is created equal—some lights, even when meant to help us see better, can make our eyes feel strained or uncomfortable. But why does this happen, especially for individuals with otherwise healthy eyes?
The conditions under which we see objects are not only a function of our eyesight but also of the surrounding luminance conditions. One of the most important components in this respect is the brightness contrast. If this brightness contrast is too large or too small, the image that we perceive has to be deciphered by our eyes with greater effort, which quickly causes discomfort.
When a background luminance value is changed from 0 to 100 cd/m², the image becomes subjectively better, i.e. contrast is increased linearly. However, above a value of 600 cd/m² a relatively dim light source can suddenly appear dazzling and cause visual discomfort. This effect is not primarily caused by the absolute brightness of the light, but by the contrast it has with its surroundings.
The “critical contrast” is the lowest possible contrast at which an object is still recognisable. If the contrast values exceed the adaptation capability of the human eye, for example, due to a too strong brightness or too small viewing angle or bad mounting position, visual discomfort occurs.
Glare is a common cause of eye discomfort. It occurs when a bright light source or reflected light overwhelms the surrounding environment. There are two types:
Direct glare, from looking toward a bright, unshielded light source
Reflected glare, such as sunlight bouncing off a polished surface or screen
Both types cause squinting, visual fatigue, and difficulty focusing, especially when the eyes can’t adapt quickly to the imbalance.
Several technical characteristics of artificial lighting can contribute to visual discomfort:
Flicker: Even when not consciously visible, flicker from fluorescent or some LED lights can cause headaches, eye strain, or migraines.
Color Temperature: Cool, blue-rich lighting can disrupt our circadian rhythms and strain the eyes, especially at night.
Blue Light Exposure: High levels of blue light from screens or LED lights can cause sensitivity, dry eyes, and interfere with sleep.
A poorly designed lighting environment amplifies discomfort. Common issues include:
Low contrast between objects and their backgrounds, forcing eyes to work harder
Uneven lighting that causes shadows and hot spots
Reflective surfaces that bounce light unpredictably
To improve visual effectiveness—a measure of how clearly objects are seen—designers can adjust illumination, contrast, and viewing angles. While boosting light levels can help when illumination is low, this approach has diminishing returns at high levels and may lead to wasted energy. A better strategy is to balance brightness, contrast, and uniformity, creating conditions that support comfort and clarity without causing strain.
Visual comfort is more than just a matter of brightness levels. It is also determined by how the light itself is perceived by the human eye, its interaction with the surroundings, and the task at hand. Studying the human perception of contrast, glare, flicker and blue light, we can create lighting that helps to improve clarity, comfort and well-being in homes, offices and public spaces.
