Younju Yoon

Analyses on Human Responses to Illuminance Variations for Resident-Friendly Lighting Environment in a Small Office

This study examines the influence of illuminance variation on visual perception and mood in a small office. Field measurements and annoyance tests were performed in a full-scale mock-up office space. Subjects conducted paper-based and computer-based reading tasks when six instantaneous fluctuation ranges were given under 500 lx and 650 lx base level conditions. Results indicate that equal amounts of instantaneous illuminance fluctuation could influence visual perception differently under these two base level conditions. Visual annoyance under the 500 lx base level was more severe than that under the 650 lx base level. The acceptable illuminance fluctuation ranges that did not cause visual annoyance under 500 lx base level conditions were 141.3 lx for paper-based tasks and 187.3 lx for computer-based tasks. Under 650 lx base level conditions, the acceptable ranges were 200.3 lx and 252.4 lx for paper-based and computer-based tasks respectively. The mean mood and perception responses for visual thresholds under the 650 lx base level showed more positive feelings than those under the 500 lx base level. Multiple linear predictive models showed that feelings of visual sensitiveness to illuminance variation, visual distraction, and stimulation were significant contributors to visual annoyance under fluctuating illuminance conditions.

Analyses on Daylight Variations for Optimum Controls of Daylight Dimming Systems in a Small Office

The influence of outdoor sky conditions on photosensor signals were examined to determine an appropriate index that is effectively used for optimum illuminance fluctuation when a daylight dimming system is used for a small office. Field measurements were conducted under various sky conditions. Results indicate that the outdoor global and vertical illuminance fluctuated within narrow ranges under clear and overcast sky conditions. The fluctuation of sky ratio under partly-cloudy sky caused wide ranges of illumnance fluctuation. A partially-shielded photosensor at backwall produced 56% of light output from fixtures controlled by a photosensor at ceiling. This implies that the photosensor at backwall does not always guarantee target illuminance due to the less output. The fluctuation of light output from fixtures were insignificant under clear and overcast sky. The fluctuation range of photosensor illuminance under partly-cloudy sky caused wide fluctuation ranges of light output. Regression result implies that the outdoor vertical illuminance was recommended for an effective index that is used for control of light output.

Applications of Control Algorithms for Dimming Operations of Electric Lighting Fixtures in a Small Office

This study examines the influence of system components of photoelectric dimming control systems on dimming control performance. Field measurements were performed and a series of computation were conducted. Continuous and integral reset control algorithms were used in connection with two photosensor shielding conditions. Results indicate that the change patterns of daylight illuminance of unshielded photosensor were similar to those of desktop illuminance. When continuous dimming control algorithm was used, unshielded photosensor conditions failed to meet a target illuminance. For the partially-shielded photosensor conditions, lighting fixtures overshot the desktop and less energy savings was achieved compared to the condition of unshielded photosensor. When the integral reset dimming control was used, the system failed to keep enough task illuminance. The desktop illuminance by electric light showed sudden peak values with no dimmed light for a particular time period. Partial shielding conditions were successful under overcast sky conditions, but no lighting energy savings was achieved. Desktop illuminance and light output correlated strongly. The ANOVA test results for the correlation were effective under a significance level of 0.01.

Validation of Computational Algorithms for Prediction of Indoor Daylight Illuminance under Sun and Sky Conditions

This study proposes computational algorithms for prediction of daylight illuminance under various daylight conditions. Five annual daylight simulation methods (ADSM) were developed for the sun and sky. Computer simulations using the ADSM were performed for a classroom with an exterior overhang. In order to validate the simulation results, the results from ADSM were compared with those by Radiance. Results indicate that the prediction by a sunmatching method and reflected daylight coefficient approach were similar to those by Radiance, when methods that consider the effect of sun were used. For the methods that consider the effect of sky, the daylight coefficient approach with four sky patches provided reliable results. The result implies that daylight coefficient approach is a useful method for the prediction of daylight illuminance under daylight conditions. Linear regression models between the results of ADSM and Radiance were acceptable with a significance level of 0.01. This implies that the ADSM can be effectively used for the prediction of indoor daylight illuminance.

Validation of Computation Algorithm for Prediction of Photosensor Signals under Sky Conditions

A theoretical method for the prediction of illuminance under diverse sky conditions was proposed in order to examine the variation of daylight illuminance at photosensors. The method was used to predict the illuminance of photosensor with a full-shielding condition. The prediction results were validated using the results of field measurement under various daylight conditions. Results imply that the predicted values were lower than those of measurement under clear and partly-cloudy sky, but the predicted values were greater under overcast sky. Percent differences between predicted and measured values decreased as the distant between window and photosensor positions increased. The coefficient of determination between predicted and measured global illuminance was greater than 0.9912 under all sky conditions. The correlation between predicted and measured photosensor illuminance was also strong under clear and partly-cloudy sky, but the correlation was weak under overcast sky. Statistical test results showed that the linear regression models between predicted and measured values were acceptable with a significance level of 0.01.

Analysis of Prediction Accuracy for Photosensor Signals of Daylight Dimming Control Systems

A computational simulation method was discussed in this study in order to predict photosensor signals under a variety of sky conditions. Theoretical approaches for a simulation method were proposed for prediction, and simulation results were compared with the results of field measurements. Results indicate that differences between prediction and measurement of outdoor global illuminance were higher under a clear sky condition compared to that under partly cloud and overcast sky condition. A photosensor positioned closer to window generated less difference between predicted and measured photosensor signals. Percent errors between predicted and measured photosensor signals under overcast sky conditions were higher than those under partly cloudy and clear sky conditions. Prediction models showed that strong correlations existed between predicted and measured photosensor signals.