Individual Control Can Be Energy Efficient
Individual Control Can Be Energy Efficient
The NRC Lighting Quality Research Project indicates that individual choice in lighting not only conformed with standards and guidelines but tended to increase user satisfaction as well. Moreover, many participants made choices that led to lower energy consumption.
Many designers, researchers, and building-services personnel Ñ not to mention the occupants themselves Ñ believe that it is desirable to give workers individual control over their own workplace environments. Prevailing opinion suggests that a personally optimized environment will provide greater environmental and job satisfaction, resulting in enhanced performance and economic payoffs for the employer. In spite of the general consensus in favor of greater individual control of office environments, there is little empirical proof of tangible benefits. In fact, some studies have shown that control can actually be detrimental.
Another point of debate is the effect that giving workers enhanced control has on energy costs. Would only certain people raise their local lighting levels, resulting in a lower ambient light level and, consequently, in energy savings? Or are preferred lighting levels so high that giving control to people who donÕt have to pay the energy bills would lead to excessive light levels and compromised energy efficiency? The questions of interest covered by the experiment included:
- What choices do people make?
- How do the choices relate to energy codes?
- How does control influence office worker satisfaction and performance?
Research Methods
This study was conducted in the same space as the first experiment. In this case, a hybrid lighting system was installed on four controllable circuits. These circuits controlled:
- recessed 1Õx 4Õ deep-cell parabolic louvered luminaires overhead
- recessed 1Õx 4Õ deep-cell parabolic louvered luminaires at the perimeter of the space
- partition-mounted indirect lighting, and
- under-shelf task lighting.
The first three circuits were continuously dimmable, whereas the task lighting had a simple on/off control. All luminaires used electronic ballasts and T8, 3 500K lamps with CRI>80.
Useable data were collected from 94 participants (47 pairs). On each testing day, two participants (matched by age and sex) were seated at the two center workstations. One participant in each pair was designated as the "lighting controller", while the other was identified as having "no control". At the start of the day the controller participant adjusted the lighting system to his/her preferences. Because of the symmetry of the space and the lighting design, the no-control participant was exposed to the same lighting conditions as the controller, but was unaware that the controller had selected the conditions. The participants then went about their ordinary office tasks for the remainder of the day, during which no further adjustments to the lighting were permitted. At the end of the session, the participants filled out a questionnaire concerning lighting quality, environmental satisfaction, and glare.
At the end of the day, the no-control participant was given an opportunity to adjust the lighting according to his/her preferences. The controller was asked, in a separate questionnaire, what changes, if any, he/she would, in retrospect, have made to the original lighting setup.
Results
Effects of control. As expected, "controller" participants felt in greater control of the lighting and of the experimental session in general; nevertheless, they did not differ significantly from no-control participants in task performance, mood, level of satisfaction or lighting quality, nor in physical sensation reports (e.g., headache, neck or arm pain).
However, our results did demonstrate that control is associated with a measurable benefit when it is used to improve environmental conditions. Statistical analysis revealed that when non-control participants were handed control of the lighting at the end of the day, they made less use of the perimeter parabolic luminaires than their counterparts who had been in control. This resulted in measurably lower levels of VDT screen glare and lower overall power demand. Interestingly, this finding was consistent with the responses of controller participants on the exit questionnaire: They reported that they would have reduced screen glare by lowering the output of the perimeter parabolic luminaires had they had an opportunity to make lighting adjustments during the day.
Lighting choices and energy use. The lighting conditions created by the controller participants were judged as highly satisfactory by both themselves and their counterparts without control. The mean rating of lighting quality was high for both groups (mean = 4.07 on a scale from 1 to 5). The satisfaction ratings did not differ between the controller and no-control groups to a statistically significant degree.
The lighting choices conformed well to the recommendations for the luminous environments in North American codes and standards. For example, IESNA RP-1 (American National Standard Practice for Office Lighting, 1993) states that desktop illuminance in spaces with VDTs should be lower than 500 lux. More than 70% of the choices made by participants met this criterion (Fig. 3).
The electrical power requirements of the lighting arrangements selected by the participants with control conformed to energy codes and standards (Fig. 3). Even though the installation allowed for choices that exceeded code guidelines, more than 80% of the selections had lighting power densities at or below the recommended level (Fig. 4). Moreover, the mean power density for the sample, at 14.3 W/m2, was 25% lower than the currently recommended density.
Discussion
The results of this study suggest that it might be wise to allow occupants to individually control their lighting environment. Most study participants reported that they would prefer to have control over their lighting, and this was associated with a greater sense of session control in general. Moreover, given the power to control their environment, controller participants tended to select lighting arrangements that were good in both objective and subjective terms. These choices were not only in conformance with standards and guidelines, but were viewed as highly satisfactory as well. No-control participants were able to improve the lighting conditions set by the controller at the beginning of the day by reducing reflected images in their VDT screens.
Finally, the results suggest that individual control over appropriately designed lighting can result in energy savings. The lit environments people selected for themselves had, on average, lower power requirements compared with environments in line with the recommendations in existing codes and standards. In other words, giving people control over lighting might result in lower energy consumption compared with a fixed lighting design.
However, no association was found between increased control over lighting and environmental satisfaction or performance. This lack of association could have one or more of the following explanations: There is no such relationship; control is beneficial only when it allows one to correct markedly poor conditions; the benefits of control are only manifest over longer periods; and benefits are only apparent when control is available continuously.
Summary
The NRC/IRC Lighting Quality research project examined lighting quality and its effects on occupants in two experiments. In the second experiment, participants, using off-the-shelf, present-day equipment for VDT offices, spontaneously chose luminous conditions well within current energy code limits for office lighting, and their lighting choices resulted in high ratings of satisfaction with the lighting. In the first experiment, energy-efficient lighting designs incorporating task and ambient lighting and using electronic ballasts, were superior in terms of a variety of task performance and satisfaction measures. Thus the evidence is clear that energy-efficient lighting, when carefully designed, can be high-quality lighting.
Guy Newsham and Jennifer Veitch
Jennifer Veitch and Guy Newsham work with the Institute for Research in Construction at the National Research Council of Canada.
The authors can be contacted at: jennifer.veitch@nrc.ca, or
guy.newsham@nrc.ca