Complaints about glare in the office: causes and solutions

How to recognise the problem

Glare in the office comes in two forms. With direct glare the employee sees the luminaire itself in their field of view. With reflected glare the luminaire is mirrored in the monitor or the glossy desktop. The second form is less obvious, because nobody looks up, but it produces the same complaints: tired eyes, headaches and loss of concentration.

Signs on a walk-round:

• Monitors stand at an angle on the desk, turned away from the ceiling luminaire.
• Luminaires are covered with paper, or staff ask whether some lamps can be removed.
• The blinds stay closed in overcast weather.
• Complaints increased after fluorescent fittings were replaced with LED.

The standard for workplace lighting asks for 500 lux on the desk, a uniformity of 0.6 and a UGR of no more than 19. Many LED replacements comfortably reach the 500 lux but not the UGR: the light comes from a much smaller and brighter surface than the old louvred fluorescent fittings.

Cause 1: luminaire luminance too high

Whether a light source causes glare depends not on the number of lumens but on its luminance: the brightness per square metre of light-emitting surface, in cd/m². A luminaire that sends 4,000 lumens out of a strip a few centimetres wide is many times brighter than a diffuse panel with the same lumens. Visible LED points behind a clear cover are the classic culprit, as is a UFO high bay in an office with a low ceiling.

For screen work the standard limits the average luminance of luminaires at viewing angles of 65 degrees and above to 3,000 cd/m², and, depending on screen type and task, to 1,500 cd/m². Check it yourself: sit at the desk, look straight ahead and raise your outstretched arm to roughly 65 degrees. Every luminaire above your hand must stay below that limit.

The solution is a larger and more diffuse emitting surface: a light line that spreads the same lumens over its full length. In addition, match the power to the room. The linear luminaires of LINEA can be set per module to 24, 32 or 40 W, so that under a low ceiling you do not light with 40 W where 24 W already achieves 500 lux.

Cause 2: wrong position relative to the screens

The second major cause is the layout. A luminaire directly behind the employee is mirrored in the monitor; a luminaire directly in front, just above the screen, sits as a bright source in the middle of the field of view. The luminaire may be fine, but it is in the wrong place.

Three rules for positioning:

• Mount light lines parallel to the viewing direction, along the length of the desks. Parallel lines give a lower UGR than lines running across the desk.
• Place the line beside the row of desks, between two rows, not above the head or directly above the monitor.
• Position desks at right angles to the window, so that daylight comes from the side.

Check for reflections by switching the monitor off: every luminaire you can see in the black screen from the workstation is a candidate for complaints, including after the desks have been rearranged.

Cause 3: high contrast from dark ceilings and walls

UGR is a measure of the contrast between the luminaires and their surroundings. A bright luminaire against a dark ceiling gives a high UGR; against a light ceiling that reflects some light itself, a lower one. The scale runs from 10 to 30 and a difference of 3 points is clearly noticeable. The standard asks for UGR 19 for desk work and meeting rooms, 22 for a reception and 28 for corridors.

The table value on a data sheet applies to a reference room with reflectances of 70, 50 and 20 per cent for ceiling, walls and floor. An anthracite grey ceiling, an open ceiling with exposed services or dark walls depart strongly from that: a UGR<21 luminaire can then end up above 22, while it stays below 19 in a white-painted office.

The solution: UGR<21 light lines with an indirect component

Anyone who wants to solve complaints for good combines a luminaire with low luminance, the right positioning and an indirect component. The linear luminaires of LINEA have UGR<21 as a table value, spread the light over their full length and can be joined seamlessly in white or black, surface-mounted or as pendants. From a ceiling height of about 2.8 m you can suspend the line as a pendant 0.3 to 0.6 m below the ceiling.

The indirect component makes the difference. With the separate LINEA uplight module you send part of the light to the ceiling, which reflects it diffusely. The ceiling becomes a large, soft light source: the contrast around the luminaire drops, the UGR goes down and shadows become softer. An indirect share of 20 to 30 per cent is enough, provided the ceiling is light, with a reflectance of around 0.7. With a dark or open ceiling you choose surface mounting without uplight.

With 120 lm/W and 24 to 40 W per module, one continuous line between two rows of desks is sufficient in many offices with a ceiling height of 2.7 to 3 m. Whether you stay below UGR 19 in your project follows from a lighting calculation with your dimensions, reflectances and viewing positions, for 350 euros excl. VAT.

Step-by-step plan for complaints

This is how to tackle a complaint in a structured way:

• Step 1: sit at the complainant's desk and look at the ceiling and into the switched-off monitor.
• Step 2: note which luminaires come into view and whether they have visible LED points.
• Step 3: measure the lux on the desk; well above 500 lux you can turn the power down.
• Step 4: assess the ceiling, the walls and the position of the desks relative to windows and lines.
• Step 5: have the room calculated with UGR per viewing position and decide whether to move, adjust or replace.

Replacement is by no means always necessary; sometimes turning a row of desks or painting a ceiling white is enough. If the problem lies in the luminaire itself, a light line with UGR<21 and an uplight module is the lasting solution. Lichtplein supplies businesses only, from European stock within 5 working days.

Frequently asked questions