Jennifer A. Veitch

LED lighting flicker and potential health concerns: IEEE standard PAR1789 update

The IEEE Standards Working Group, IEEE PAR1789 “Recommending practices for modulating current in High Brightness LEDs for mitigating health risks to viewers” has been formed to advise the lighting industry, ANSI/NEMA, IEC, EnergyStar and other standards groups about the emerging concern of flicker in LED lighting. This paper introduces power electronic designers for LED lighting to health concerns relating to flicker, demonstrates that existing technologies in LED lighting sometimes provide flicker at frequencies that may induce biological human response, and discusses a few methods to consider when trying to mitigate unintentional biological effects of LED lighting. The paper represents on-going work in IEEE PAR1789 that is vital to designing safe LED lamp drivers.

Assessing Beliefs about Lighting Effects on Health, Performance, Mood, and Social Behavior

Energy conservation through the adoption of new, energy-efficient technologies will succeed only to the extent that the new technologies are not themselves perceived as risk sources. Previous research has found that beliefs about the health effects of fluorescent lighting predict compact fluorescent lamp use in homes. This paper describes the development and validation of a questionnaire to assess beliefs about the effects of common types of interior lighting on human health, work performance, mood, and social behavior. Principal components analysis of the 32-item Lighting Beliefs Questionnaire revealed 6 interpretable components: Lighting Importance, Brightness, Major Health Effects: Fluorescent Lighting, Minor Health Effects: Fluorescent Lighting, Social Setting, and Daylighting. The questionnaire may be used to explore responses to interior lighting and to discover what beliefs are held by end users. This information will assist in allaying unwarranted fears and concerns about new lighting technologies.

Modulation of fluorescent light: Flicker rate and light source effects on visual performance and visual comfort

The effects of fluorescent light spectral composition and flicker rate on visual performance and visual comfort were studied on 48 undergraduate students using two different rates of flicker: conventional low-frequency flicker (120 Hz) and high frequency flicker(between 20-60 kHz); and three different light sources; full-spectrum lamps, cool-white lamps, and filtered-cool-white lamps. The design was a 2 X 3 (Flicker rate X Light source) mixed within-between ANOVA. Visual performance and time on visual performance task were assessed using a Landolt ring task. Visual comfort was assessed by self-report after a period of reading difficult text. Visual performance scores of 18-24-year-old male and female university students were significantly higher in the high-frequency flicker condition than the low-frequency flicker condition. There were no other statistically significant effects. Health status was unrelated to visual performance. Neurophysiological explanations are discussed. The finding that an energy-efficient means of driving fluorescent lamps also can improve visual performance provides added impetus to adopt this new technology.

A critical examination of perceptual and cognitive effects attributed to full-spectrum fluorescent lighting

Full-spectrum fluorescent lighting (FSFL) has been credited with causing dramatic improvements in vision, perception and cognitive performance as compared with other fluorescent lamp types. These effects are hypothesized to occur because of similarity between FSFL emissions and daylight, which is said to have evolutionary superiority over other light sources. This review, covering 1945-98, critically considers the evidence for these claims. In general, poorquality research has resulted in an absence of simple deterministic effects that can be confidently attributed to fluorescent lamp type. Promising avenues for lighting- behaviour research include investigations of cognitive mediators of lighting—behaviour relationships, and flicker rates and colour rendering effects on visual processing, appearance judgements and affect. Good lighting solutions are more complex than lamp type specification.

Lighting quality recommendations for VDT offices: a new method of derivation

An experiment in a mock-up office space gave occupants control over dimmable lighting circuits after a day working under pseudo-random lighting conditions. Data analysis indicated that the lighting experienced during the day influenced the changes in lighting made at the end of the day. Occupants chose to reduce screen glare if any existed. Even after allowing for the effect of glare, desktop illuminance at day’s end varied with the illuminance experienced during the day. Regression of these end-of-day choices relative to the illuminance experienced during the day can yield a preferred illuminance, equivalent to the daytime illuminance at which no change was preferred at day’s end. Using this method, preferred illuminances in the range 200-500 lux were derived. Preferences for luminance ratio were also derived. Interestingly, the deviation between participants’ lighting preferences and the lighting they experienced during the day was a significant predictor of participant mood and satisfaction.

Linking Lighting Appraisals to Work Behaviors

Among those concerned with practical matters of office design, demonstrations that the work environment affects employees’ well-being and work behaviors are thought to be important to support client decision making. Veitch, Newsham, Boyce, and Jones developed a conceptual model in which lighting appraisal and visual capabilities predicted aesthetic judgments, mood, and performance. This article extends that model to include measures of work engagement, using experimental data originally reported by Newsham, Veitch, Arsenault, and Duval. Structural equation modeling showed strong fit to a model in which lighting appraisals indirectly influenced work engagement through aesthetic judgments and mood. This evidence that providing a satisfactory work environment can contribute to employee effectiveness merits further study by environmental and organizational psychologists.

Effects of office environment on employee satisfaction: a new analysis

Two large and detailed field studies of the effect of office environment parameters on aspects of environmental and job satisfaction were conducted. The first study focused on open-plan offices in nine conventional buildings, whereas the second encompassed open-plan and private offices in 24 buildings (12 green and 12 conventional). The data collection for these studies was separated by approximately a decade, but the data collection methods, contexts and analysis procedures were very similar. This offered the opportunity to compare the results of the studies at the workstation level, with the goal of identifying parameters consistent in affecting occupant satisfaction, and of exploring the effects of office type (open-plan versus private) and building type (green versus conventional). Satisfaction with acoustics and privacy was most strongly affected by workstation size and office type; satisfaction with lighting was most strongly affected by window access and glare conditions; and satisfaction with ventilation and temperature was most strongly affected by pollutant concentration. Occupants of green buildings rated all aspects of environmental satisfaction more highly. Finally, job satisfaction was most strongly affected by pollutant concentration and office type.

Preferred Chromaticity of Color-Tunable LED Lighting

Abstract Previous research has demonstrated that individual personal control over light level benefits individuals and organizations. As a first step toward testing whether light source spectrum choices—which are possible with light emitting diode (LED) systems—offer similar benefits, we examined preferences for various spectra in a scale model of an office. Participants judged the model’s brightness, colorfulness, and pleasantness when lit with five preset spectra with measured correlated color temperatures (CCTs) of 2855, 3728, 4751, 5769, and 6507 K created with five LED channels and one fluorescent spectrum (3750 K measured), all at approximately 500 lx. Then they chose their preferred light spectrum using the five LED channels, once as a free choice and once with an illuminance limit. Judgments of the fluorescent spectrum and the LED spectrum with the closest (matched) CCT did not differ. The preset judgments followed a quadratic pattern, with the lowest and highest CCT conditions having lower ratings than the three middle conditions. The free and illuminance-constrained lighting choices did not differ, with individuals’ selections ranging from 2850 to 14,000 K and generally lying slightly below the blackbody curve.

The Effects of Fluorescent Lighting Filters on Skin Appearance and Visual Performance

(2002). The Effects of Fluorescent Lighting Filters on Skin Appearance and Visual Performance. Journal of the Illuminating Engineering Society: Vol. 31, No. 1, pp. 40-60.

Control strategies for lighting and ventilation in offices: effects on energy and occupants

Participants (N=126) spent a day in a full-scale office laboratory, completing questionnaires and standard office tasks. Some participants experienced typical constant lighting and ventilation conditions, whereas others were given personal control over the dimming of lighting in their workstation and over the flow rate of air from a ceiling-based nozzle in their workstations. Half of the participants, some with personal control and some without, were exposed to environmental changes typical of demand—response load shedding in the afternoon: workstation illuminance was reduced by 2% per minute, and ambient air temperature increased by ∼1.5°C over a 2.5 hour period. Results showed that personal environmental control improved environmental satisfaction. Personal control over lighting led to an average energy reduction of around 10% compared to a typical fixed system; participants with personal control also reduced flow rate compared to the constant condition. Use of each control type averaged two—three control actions per person per day, which dropped to less than one control action per person per day in a longer-term pilot study (N=5) conducted in the same space. Load shedding had some small negative effects for occupants, but in practice is unlikely to create substantial hardships, and is a reasonable response to peak power emergencies.