Luminance - in theory and practice
How does luminance affect our experience of a space and its function?
Illustration 1 - Good lighting in a classroom: "Efficient lighting with proper luminance distribution creates a comfortable and functional learning environment. Luminance is evenly distributed, providing a visual comfort that promotes concentration and reduces fatigue."
Light plays a crucial role in our perception of the space around us. Among the many parameters that describe light, luminance is one of the most significant as it directly relates to how we perceive the light intensity from a surface.
What is luminance?
Luminance describes how we perceive the light intensity from a surface. It is measured in candela per square metre (cd/m²) and depends on both how much light a surface reflects and how the light hits the surface. A bright surface such as a white wall will have high luminance, while a dark surface will have low luminance.
Luminance differs from other light measures such as luminance lux, which is about how much light falls on a surface. Luminance is about how we perceive the light reflected from the surface. A high luminance area will appear lighter to the eye, while a low luminance area will feel darker. It's important to note that the eye's ability to perceive contrasts between different luminance levels is crucial to our ability to navigate and understand space.
For example, even if a room receives a lot of light (high lux), it can still feel dark if the walls absorb the light instead of reflecting it. On the other hand, a room with less light can feel brighter if the surfaces reflect the light well.
Visual comfort with luminance ratio
Luminance ratio refers to the difference in luminance between different surfaces or objects within the same field of view.
Illustration 2 - "Insufficient lighting with large luminance differences can create discomfort and reduce visibility. Here, shadows and glare can lead to visual overload and make it difficult to concentrate for long periods of time."
Excessive differences in luminance can lead to visual discomfort as the eye has to constantly adapt. For example, a very bright computer screen in a dark room can lead to eye fatigue because the contrast between the screen and the surroundings is too high.
For visual comfort, the luminance ratio between primary and secondary surfaces should be balanced. Contrasts should be sufficient to create depth and texture in the space, but without overloading the eye.
It's not necessary for everything to be the same brightness - quite the opposite. Contrasts add depth and help us orientate ourselves, but they need to be balanced to avoid straining the eye. This is especially important in work environments where screen work, reading or precision tasks require high visual comfort.
Luminance not only determines how we perceive a space, but also how we use it. A well-considered luminance distribution can enhance the functionality of the room so that tasks such as reading, cooking or working can be carried out efficiently.
For example, a work environment where screen work or precision work is common requires lighting that avoids glare and shadows, providing a comfortable and productive working environment. In a retail environment, on the other hand, it is important that the lighting emphasises the products in a way that makes them easy to see and creates a welcoming atmosphere that encourages customers to interact with the products.
Luminance can also be used to create mood in a room. Light and shadow can be used together to create anything from a cosy atmosphere to a dramatic effect, depending on the intended use of the room. Besides function and mood, luminance distribution is also important for safety. Good luminance distribution can help reduce the risk of accidents by making steps, edges and other potential hazards clear and visible.
By understanding and working with luminance when creating lighting solutions, visual and functional needs can be optimised when designing spaces.
