Light & Glare

Added: 25/05/22

In the natural world, we would not be forced to look directly into the sun. In the built environment, however, we are often faced with a window or a light fitting that is directing the light into our eyes without a diffuser or shade. The eye struggles to adjust to the light levels and that triggers a powerful stress response. The eyes move around incredibly fast, the blink reflex is activated, and the pupil dilates and contracts. This “glare” is a stressor, but is it the main form of visual discomfort?

In the built environment we talk about two types of glare - direct glare - where the light shines directly into your eyes - and reflected glare - where it bounces off shiny surfaces and screens. The lighting industry has created a ‘glare rating’ and it’s a way to measure the level of discomfort that an average person would experience in that setting. There are different recommended ‘glare ratings’ for different settings with 19 being the threshold in most situations.

You can ensure that the luminaire itself is designed to minimise the glare but there really is no substitute for being in the space yourself to experience the light first-hand from different positions and at different times of the day. Choose a luminaire that you can focus on or adjust to fine-tune the effect. At Phos, our range is entirely adjustable both before and after installation allowing complete harmony in design.



Glare is not the only thing that causes visual discomfort. The distribution of light within a space is equally important.

The eye adjusts like a camera to different light levels and uses shadows and contrast to identify forms in space and intuitively prefers spaces with a range of light levels.  A natural scene offers a range of luminance with around 50% difference between the brightest and darkest zones so replicating this in the built environment is important. We need light bounce to bounce off a range of different surfaces and textures in a scene to create a varied but broadly even range of light levels. We can see clear preference for images with even distribution of luminance across the scene when we measure response from pleasure centres and track the movement of the eye. (Graham, Daniel & Schwarz, Bianca & Chatterjee, Anjan & Leder, Helmut. (2015).


Contrasting zones of bright and dark in a space, particularly a transitional space like a corridor, can create an extremely uncomfortable feeling and the the ‘window’ of the eye adjusts for the brighter areas which means that your brain is not getting enough information to make out the darker areas, creating a feeling of threatening discomfort.

High contrast zones in a space affect our ability to move confidently between dark and light areas. The pupil expands and contracts to let in the correct amount of light which takes up to 30 minutes to accommodate fully from bright to dark conditions. This means that when we move from a bright area to a dark area, for a moment or two, it’s hard to see and you might feel a bit disoriented or literally caught ‘off balance’. Picture driving or walking in bright sunshine and suddenly entering a tunnel. It feels really dark until your eyes ‘catch up’ or when you’ve been sitting indoors and step outside into the sunshine. This response gets slower with age and with other neurological conditions, which is why most trips and falls happen at thresholds or areas where there is a sharp transition between light and dark areas of space.

The remedy? Use a flexible range with interchangeable optics and softening lenses. Get light to where it needs to be in a way that is soft and organic. Phos fittings are built with flexibility in mind, offering a huge amount of flexibility in design.

Not only do we prefer scenes that reflect a ‘natural’ luminance distribution from a psychological perspective, but there are practical/physical reasons why scenes that offer softer graduations are easier on the eye and brain.

Discomfort from the physical adjustment to light levels is one issue - lighting can also generate psychological unease. If you consider that we evolved under the sun from above, the position of the light falling on another person will give us vital information about where they are relative to us and to potential escape routes . Take a look at these faces, they all have the same expression, but our feeling about them is very different. It’s very important to consider the position of the lights, especially in spaces that involve interaction - social and work - including your set-up for a zoom call!


LED’s are either on or off. To dim, they must be turned off at regular intervals to reduce the total light released. The issue is that our brains are finely tuned bits of kit and can sense this. Sometimes it is obvious, but much of the time it is not. This “non-visual flicker” strains the brain, which works hard to remove the flicker to create a fluid and harmonious experience of the world around us. This flicker from LED lights causes headaches and eye strain, epilepsy and reduces reading speed and accuracy.

Flicker can be created at any stage in the lighting system - from the power input to the switch (especially dimmers) and the luminaire itself. Phos project managers combine with our technical team to ensure non-visual flicker is removed from our fittings, either through use of our non-flicker mains dim drivers or by using more advanced dimming protocols such as 0-10V and DALI.


Glare is one of the biggest contributors to visual discomfort but it is not the only one. Our brains are complex bits of kit and in order to replicate the natural world and optimise the built environment for human beings, you need great products, attentive project managers and the ability to finesse once all items in a project have finally been installed.







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