Investigating light level on the perceptions of optimal illuminance : enhancing workplace comfort for occupants in Sri Lanka

Abstract

The recommended illuminance level values applicable for Sri Lanka are specified in the ‘Energy Efficiency Building Code of Sri Lanka’, published in 2021. These illuminance level values were obtained from the ‘CIBSE code of interior lighting’, published in the United Kingdom in 1994. Considering the differences in the climate, culture, technology, economy etc. in the United Kingdom and Sri Lanka, developing and implementing illuminance level recommendations specifically for Sri Lanka could improve the comfort, performance, health etc. of the occupants. For the general offices, the optimum illuminance level for Sri Lanka has been identified as 300 lx considering the performance, while the recommended illuminance level at present is 500 lx. Among the other aspects which are to be considered to develop an illuminance level recommendation, this study focuses on deriving the most accepted illuminance level for general offices, based on the perception of the occupants. A survey was conducted to obtain the perception on available illuminance levels and illuminance measurements. The average of the available illuminance levels was 297.71 lx. Only 10.18% of the readings complied with the recommended illuminance level. The most accepted illuminance level based on the perception was derived to be 255 lx. These results were verified by conducting the same study for a sample of employees who work in laboratories, since the recommended illuminance level for laboratories is the same as for offices. Further, the calculations revealed that the installation cost and energy cost for the most accepted illuminance level are 50% less than the cost for the recommended illuminance level. The method used in this study to obtain the most accepted illuminance level for the occupants of the offices is suggested to be extended to other types of workplaces in developing recommended illuminance level values considering the Sri Lankan context.