How many assessments have you done, where the main issue has been related to office lighting, be it migraines, excessive reflection, glare etc. Do you routinely measure lux? If so how useful is this?
What is lux? It is a measure of illumination and one lux is equivalent to the amount of luminance from one candle. It can be easily measured using readily available lux metres and should be between 300 and 500 for office environments, at the higher end where there is increased use of paperwork and potentially lower where screen use is primary.
What is glare? Glare occurs when one part of the visual field is much brighter than the average brightness to which the visual system is adapted. When there is direct interference with vision the condition is known as 'disability glare'. Where vision is not directly impaired but there is discomfort, annoyance, irritability or distraction the condition is 'discomfort glare' and is what most of our clients will report.
So the degree of lux and the amount of glare are not the same thing and in many ways are not related. So how important is lux, or the degree of illumination of a workstation? Well, office work is visually demanding and requires good lighting for maximum comfort and productivity. "Good" lighting means providing enough illumination so that people can see printed, handwritten or displayed documents clearly but are not blinded by excessively high light levels. The level of lighting requirement is different for different people. Requirements usually increase with age and as stated will increase with greater use of printed material, particular if that material is fine print. Since these requirements are so individualised, a sensible approach to office lighting may be to set the general luminance around the 300-400 lux mark and then provide desk lamps to increase luminance where required. This has been shown by the Society of Light and Lighting to reduce overall energy costs.
So if insufficient lux is not what we encounter for the most part, how do we deal with discomfort glare. Well, this can be one of two types: Direct and reflected: Direct glare involves a light source shining directly into the eyes — ceiling lights, task lights, or bright windows. To determine the degree of direct glare, you can temporarily shield your eyes with a hand and notice whether you feel immediate relief (I will often raise my folder to the light and ask the user if they notice a difference). This will give you a good indication of how removing or reducing that light source will benefit. Reflected glare, such as on computer screens, sometimes causes eyestrain. But its worst effect may be causing you to change your posture to an uncomfortable one, in order to see well. Many users will request anti glare screens but be aware, the vast majority of new screens have inherent anti glare properties and adding an additional light filter will not address the reflection and it is the source of the glare that needs to be reduced. Often direct glare from the screen itself (brightness too high) can be mistaken for reflective glare. Reduce the brightness to minimise contrast between the screen and the ambient light to control this.
So. There are some easy practical ways to control discomfort glare. If you want to measure it you can, but this requires a rather complicated equation to give you a Unified Glare Rating (http://www.sciencedirect.com/science/article/pii/S0360132314003485)
My advice: measure the luminance if necessary and tackle the main source of glare using practical measures discussed, which might include the SuperVisor from Posturite (http://www.posturite.co.uk/monitor-cpu-solutions/screen-filters/supervisor-clamp-mount-anti-glare-screen.html).
Office lighting - What's lux got to do with it? A little bit!