Excessive luminances or luminance contrasts may also lead to a visual sensation called glare, which, even though it is also light, can impair or disable vision rather than enable it….
Excessive luminances or luminance contrasts may also lead to a visual sensation called glare, which, even though it is also light, can impair or disable vision rather than enable it. Glare is categorized as several different types according to its effects.
Direct glare is caused by directly viewing a light source, such as a bright window or an unshielded high-brightness lamp. Reflected glare is caused by light reflected from a surface, such as a veiling reflection on a glossy magazine or computer screen.
If the bare lamp is visible to the user’s eye, even if is visible above the natural cutoff angle of the eyebrow, users may find it much more comfortable to shield their eyes with their hand or a baseball cap—a condition called overhead glare. Graphic courtesy of Naomi Miller.
is particularly dangerous because vision is virtually disabled. Discomfort glare
occurs when glare sources in the field of view produce a sensation of irritation in the eye. One type of discomfort glare that may occur in open office plans, classrooms and similar environments is overhead glare
, which, unlike the usual discomfort glare, does not occur within the field of view. Instead, it is caused by people performing heads-up tasks, such as office workers typing on keyboards or students observing a teacher, under recessed 2×4 luminaires. The sensation of brightness fades below the line of sight to the glare source, producing a sensation of glare due to light scattering at eyebrow and cornea of the eye. Light may also be reflected into the eyes from the face around the eyes, such as the nose and cheekbones.
What to do
If glare is present, consider the source, the task and their relationship with each other and the user. Changing one or a combination of these should be able to solve most glare problems.
Regarding the source, avoid direct sunlight penetration into the space. Bright windows can be mitigated by placing light on adjacent walls to reduce contrast or providing shading. Avoid excessively bright lamps in luminaires where the lamps are visible. If bare lamps will be a potential source of glare, consider low-brightness luminaires.
Regarding the task, consider placing light on the task’s surround to reduce contrast. Consider changes to the source/task/eye geometry that may solve the problem, such as relocating or reorienting the task. Reflected glare on computer screens should be less of a problem than it was just a few years ago as computer screens have advanced considerably—larger radius of curvature, improved screen brightness, anti-reflectance technology, flat screens, positive contrast in software, etc.—thereby reducing the risk of unwanted reflections.
While glare is typically best avoided, in some cases it can be welcome, such as tiny points of high brightness, or “sparkle,” used to convey an atmosphere of elegance. Examples include bright highlights on silverware in a fine restaurant or in a chandelier mounted over a grand lobby.