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Dealing with glare: improving visual comfort

In this exclusive extract from NBS Shortcuts, written by noted industry figure Austin Williams, we introduce the concept of glare.

Even though it is difficult to define, and hard to remedy, glare is often a contributory factor affecting the proper use of computer screens, leading to personal discomfort, and affecting the health, safety and performance of personnel. Contrary to what R.E.M. tells us, "shiny" does not necessarily make for happy people.

Understanding the effects and causes of glare, or "apparent brightness" as it was called by R G Hopkinson way back in 1941, has given rise to a huge industry in research papers since the 1950s. Interestingly, much of it is still subjective with some studies measuring pupil dilation, and others seeming to rely on human testimony; with surveys containing categories of personal assessments such as: "intolerable", "disturbing", "noticeable" and "imperceptible".

Alan Gilbertson's recent guide for the Construction Industry Research and Information Association (CIRIA), CDM2007 - Workplace "in-use" guidance for designers, points out that glare from electrical lighting may induce headaches, and helpfully suggests that, so far as is reasonably practicable: "incidences of unshielded glare or flash should be eliminated". It also points out that glare may inadvertently exacerbate slip and trip hazards. However, the Construction (design and management) regulations 2007 include only a few, minor references to the problems associated with inadequate or inappropriate lighting in buildings, simply noting that: "Every place of work and approach thereto and every traffic route shall be provided with suitable and sufficient lighting, which shall be, so far as is reasonably practicable, by natural light". The Workplace (health, safety and welfare) regulations 1992 does not raise the issue of glare at all but, with minor grammatical differences, contains the same sentence about suitable lighting as that contained in CDM 2007.

Light and shade

In fact, the issue of glare is more than a physiological health and safety issue. Some studies suggest that unevenly distributed daylight can cause psychological harm and frequently leads occupants to close blinds and switch on lights, resulting in the unnecessary use of electricity. Unanticipated glare can also have repercussions in emergency situations. For people escaping from smoke-filled rooms, for example, visibility is key: confronting an Anthony Gormley-esque Blind Light situation - the disorienting installation at Tate Modern - can easily cause confusion and panic. Care should also be taken with the location and direction of external lighting, especially when located near highways, to prevent distracting or temporarily blinding drivers.

The experience of glare is often premised on the response to sources of light within the field of view that are deemed to be too bright relative to the background against which they appear. The International Commission on Illumination, otherwise known as the Commission Internationale de l'Eclairage (CIE), is the international standardisation body for the science of lighting. Its method of glare assessment - used as the universal standard - is the Unified Glare Rating. The CIE defines glare as "visual conditions in which there is excessive contrast or an inappropriate distribution of light sources that disturbs the observer or limits the ability to distinguish details and objects". From this, the Chartered Institution of Building Services Engineers (CIBSE) describes two types of glare:

Disability glare is defined as the situation where "vision is impaired by excessive dazzle from a bright light source or reflection such as light reflecting from a glossy surface or from water"
Discomfort glare is defined as "visual discomfort... caused by very bright light such as direct sunlight or bright lamps". When shiny surfaces are illuminated the resulting reflections, called veiling reflections, produce bright patches of high intensity light.

The discomfort of veiling reflections are often seen on display monitors where the reflection of a luminaire might sometimes block out part of the visible screen. Often, when a monitor is placed, say, in front of a south-facing window, the user may experience disability glare in the form of the intense background light silhouetting out the screen.

Find out more

The full text of this NBS Shortcut is exclusively available as part of a subscription to NBS Building Regulations.

NBS Shortcuts is a new series of illustrated "how-to" articles and guides, covering a wide range of practice, regulatory and design guidance. The easy to follow text and detailed hand-drawn graphics will aid any building designer. They are available online as part of your subscription to NBS Building Regulations.