The weekly incidence of headaches among office workers was compared when the offices were lit by fluorescent lighting where the fluorescent tubes were operated by (a) a conventional switch-start circuit with choke ballast providing illumination that pulsated with a modulation depth of 43-49% and a principal frequency component at 100 Hz; (b) an electronic start circuit with choke ballast giving illumination with similar characteristics; (c) an electronic ballast driving the lamps at about 32 kHz and reducing the 100 Hz modulation to less than 7%. In a double-blind cross-over design, the average incidence of headaches and eyestrain was more than halved under high-frequency lighting. The incidence was unaffected by the speed with which the tubes ignited. Headaches tended to decrease with the height of the office above the ground and thus with increasing natural light. Office occupants chose to switch on the high-frequency lighting for 30% longer on average.

This paper reports daily and seasonal patterns of lighting use in offices where occupants were able to vary the level of illuminance falling on their working areas. The results show that occupants set a wide range of illuminances, many of which are significantly below CIBSE Code recommendations leading to significant energy savings throughout the year. Although users report use of controls for a variety of reasons, the results of the long-term monitoring of switching behaviour reveals that very few in fact use them for anything other than to switch on upon arrival at work, with further use of systems during the day being rare. Evidence suggests that the way in which systems are configured exerts influence over the level of electric light occupants work under. There is some evidence of an effect of daylight availability on levels set but little evidence to suggest pervasive and consistent user preferences for levels of electric light.

The use of locally addressable dimmable lighting systems has been examined in 14 open-plan office buildings. This paper discusses user attitudes toward control systems and the luminous conditions they produce. The majority of users are satisfied with both the quantity and quality of light on their workstations and are generally positive towards systems. This is despite large numbers of them working in illuminances significantly below current CIBSE recommendations. This indicates a significant potential for energy saving, since increased personal control leads to the use of lower lighting levels without detriment to occupants’ perceived lighting quality and visual comfort.

A study of 14 open-plan offices equipped with occupant controlled general lighting recorded achieved workstation lighting conditions at a number of times of the year. The results confirmed the occurrence of a wide range of workstation lighting levels, many significantly below CIBSE Code recommendations, with average electrical loadings due to lighting in the order of 55% of maximum. System con-figuration had a significant influence on luminaire output, illuminances and energy consumption. In general the lowest luminaire outputs were in buildings where the default reset level was to a low output, with the highest outputs being in buildings having high reset levels and large control groups. In addition locally sited control devices were associated with lower luminaire output.

This paper reviews the current uniformity recommendations and shows that they may no longer be appropriate. A study to investigate the acceptable illuminance uniformity across a desk top is described. The illuminance patterns used were representative of those produced by over-spaced luminaires, selective luminaire dimming, e.g. using HF regulation, or lamp failure. Subjects were asked to carry out simulated office tasks and then to rate the various attributes of the lighting and its acceptability. Their task performance was also measured. The results showed that although the subjects were aware of the lack of evenness of the lighting, for tasks which occupied only part of the desk, an illuminance uniformity across the desk below current recommendations was acceptable and task performance was unaffected.