Electrical lighting in open-plan offices. A laboratory study and simulations on lighting preferences and enegy use.

The need for energy use reduction raises the question of electrical lighting use especially in the non-residential sector. Office spaces are particularly sensitive in this area, as lighting is quite essential, and connected to satisfaction, mood and performance. Literature suggests a wide variety of preferred conditions, although most of the studies refer to older ways of working. This thesis explored the lighting conditions’ preferences through a laboratory study, by exploring the switch-on probability of task light when working in low illuminance levels. On a second level the results of the laboratory study were used to feed simulations on illuminance levels, uniformity and energy use in a hypothetical open-plan office. Through this project, it was revealed that a reduction on illuminance levels is possible and with daylight implementation can lead to remarkable savings in energy. Finally, lighting preferences are crucial to be investigated further.Individuals have their own lighting preferences, when it comes to relaxing, studying or working. But what happens when many individual preferences co-exist in the same space? Although there are requirements considering the lighting levels needed for working and the evenness of the lighting provided, individual preferences affect them in bigger complex spaces. This study is exploring the boundaries of these requirements in order to save energy without compromising lighting quality. A laboratory experiment is the first step of this study. For the purposes of this study, 22 people were asked to work on a laptop, in a room fully covered to exclude any exterior light. The lighting in this room was set to 100 lx. In order to understand these conditions, 100 lux is the condition of a dark heavy-clouded day here in Sweden. The total duration of the experiment was 30 minutes and every participant had the possibility to switch-on a task lamp to raise the lighting up to 300 lx. For all the participants, lighting was measured by a sensor, in order to find out how many of the participants decided to switch-on the task lamp. The percentage of people that switched-on the task lamp is the switch-on probability and was used further on this thesis. After the end of every experimental session, three identical questions were asked to all participants. Those questions are: Do you prefer to work in darkness? Do you ever use task lighting? Do you actively turn on/off lighting? The answers to these questions were used as additional information on preferred lighting environment. This first part resulted that 6 out of 10 people, when they work in low light conditions need to switch-on a task lamp. The interview part revealed a lot also. Although the questions required a yes or no as an answer most of the people felt comfortable to add more comments. Most of the participants felt comfortable to talk about their preference in lighting levels, while some of them mentioned a dissatisfaction with the task lamp generally and during the laboratory study. The results of the switch-on probability were used as input data for the simulations of lighting conditions in an open-plan office, for the second part. In this part, three different scenarios of lighting environment were simulated. The first scenario was a general system providing 500 lx in the horizontal level and uniformity, which expresses the evenness of provided light, of 0.6 as required by the standards. In the second scenario the conditions of the laboratory study were recreated, while the location of the task lamps that are on, were simulated randomly in three different cases, to have more objective results. In the last third scenario, daylight was also taken into consideration. The first two scenarios were examined in terms of horizontal illuminance and uniformity, while all three scenarios were examined in terms of energy use. The three different simulated scenarios showed that uniformity is affected by different behaviors in an open-plan office and it cannot be maintained in the initial level. Moreover, the energy use was reduced with the illuminance levels reduction by 59 %, while in the same conditions, daylight utilization reduced the energy use additionally by 48 %. To conclude, uniformity as a metric is prone to human behavior and cannot be a guarantee of a good lighting environment of more complex spaces. Illuminance reduction is possible and is essential to energy use reduction. Finally, daylight can lead to bigger energy savings