In a typical contemporary commercial building, artificial lighting is one of the larger
energy consumers, accounting for approximately 30 - 40% of the energy consumption
(Massey University, 1 992). There is considerable scope for significant reductions of energy. The operation of artificial light largely coincides with peak electricity tariffs and new technology for energy efficient office lighting has shown that energy savings
of up to 40% are achievable (Centre for Advanced Engineering, 1 996).
In many commercial buildings, energy efficient triphosphor fluorescent lamps have superseded halophosphate lamps. These lamps have increased light output, minimal
depreciation, a greater lifespan and better colour rendering than halophosphate lamps that are currently used for lighting general office spaces.
Electronic ballasts offer significant energy savings over magnetic ballasts, reducing energy consumption by up to 30%, increasing the life of fluorescent lamps and offering flicker free operation. Magnetic or low frequency ballasts are available as either regular or low loss. The low loss ballasts do not offer the additional benefits of electronic ballasts, but have significantly lower energy consumption.
A less apparent cost of inefficient artificial lighting is the generated waste heat and subsequent demand for chilling in an air-conditioned building. Energy efficient lighting that utilises appropriate lamps, control gear and luminaires require fewer lamps and less heat is produced.
These benefits are already ensurmg a steady uptake of triphosphor lamps and increased use of electronic ballasts in commercial buildings, regardless of any potential benefits to occupants within the office spaces. Further research is required to determine if energy efficient triphosphor lamps and electronic ballast's will impact upon the productivity of office workers, and thus it's economic feasibility and attractiveness to the consumer.
1.3 Summary
Fluorescent light flicker has been highlighted as a potential contributor to asthenopic symptoms experienced in the workplace and has been shown to affect visual performance, fatigue and satisfaction with the lighting (Brundrett, 1 97 4; Wilkins et al., 1 989). A large number of factors influence the perceptibility of the flicker including: • Ballast type • Lamp characteristics • Lamp age • Office configuration • Occupant characteristics
However, research suggests that provided lamps are well maintained, only a small proportion of occupants are likely to be able to perceive lamp flicker (Collins &
Hopkinson, 1 954). This is an important area for future investigation. There is a lack of field studies that evaluate the relationship between flicker perception, lamp maintenance, health symptoms and environmental satisfaction, particularly with modem installations.
In addition to the perception of visible flicker, lamps operating with low frequency ballast's have been shown to influence the physiological responses of the eye and neurological pathways. Visual neurons respond to flickering light at frequencies well above those present in lamps operated with low frequency control gear, firing synchronously in response to the luminous modulation. This subconscious response has been shown to result in less accurate processing of visual information. Several studies have found that flicker frequency can influence visual fatigue, subjective discomfort, post task visual performance, headaches and eyestrain, although this has not been demonstrated in all research. It is theorised that it is these unconscious mechanisms that cause the asthenopic symptoms reported by subjects working under fluorescent lighting (Wilkins, 1 99 1 ) 1 5•
There is evidence to suggest that some physiological conditions can increase sensitivity to flicker, resulting in more asthenopic symptoms in susceptible populations. The only significant field study (Wilkins et al., 1 989) found that headache and eyestrain symptoms were more than halved under high frequency lighting when compared to low frequency lighting. In the study, the occupants carried out a work task at supra-threshold levels. Only a small proportion of the participants experienced headache and eyestrain symptoms. These participants may have been more sensitive to fluorescent light flicker, however the study did not cite the proportion of the participants who could detect flicker or participant demographics.
Future studies should monitor other aspects of the building and occupants' perceptions in order to determine the extent to which lighting contributed to
symptoms in relation to other environmental parameters. In addition, these studies would benefit from collecting the history of vision related health problems and detailed demographic information from participants in order to evaluate predisposing factors that may influence symptoms.
Increasing flicker frequency has been shown to improve task performance on some measures (visual performance, verbal intellectual, psychophysical and reaction speed). These studies had significant visual components. Veitch (2000) suggested that 'the effect of flicker is limited to visual processing only, and does not influence other cognitive processes (arousal and stress)'. This is reflected in studies that have shown
flow-on effects including decreased visual comfort and asthenopic symptoms.
The influence that chromatic modulation has on perceptibility, asthenopic symptoms and visual performance is not clear. Although the persistence of the phosphors influences the modulation depth, this difference has not been shown to significantly affect symptoms in office populations, although it may be influential in some groups.
Taken together, the research strongly suggests that the flicker from low frequency fluorescent lighting may influence the health symptoms, performance and satisfaction of office personnel. Imperceptible flicker may influence visual processing, leading to increased visual fatigue and decreased task performance. In addition, susceptible populations may be able to perceive flicker from lighting installations using low
frequency ballasts. These personnel may experience a higher incidence of visual
discomfort in comparison to other office staff.
Laboratory research has yielded a valuable understanding of the role of fluorescent light flicker in relation to visual performance tasks. However it is not without the
limitations of a laboratory experiment (Kerlinger, 1 968; Boyce, 1 98 1 ; Goldman,
1 994). The isolation of the setting, the desire to perform at one's best, the short time
period, and small population group are all factors that suggest that further research in
a field setting is required.
Specifically, the interventional field study completed by Wilkins et al. (1 989) should be repeated to validate the effect that changing flicker frequency had on symptoms
experienced by office personnel. This study could be extended to include modulation depth as a lighting treatment and the questionnaire should include the participants satisfaction with lighting conditions, including detection of flicker in the office environment.
In addition, laboratory research has shown that flicker frequency affects visual performance, and further research in a field setting is necessary to determine if there is a flow on effect on actual productivity in the work place.
Taken together, the literature strongly suggests that one obvious research direction for further exploring the effect of fluorescent light flicker on office personnel is via further field research. The interventional study by Wilkins et al. (1 989) suggests a valuable starting point in developing an appropriate methodology.