Pilot study on a new approach for estimating spatial brightness of a room

Lin Ching-Wei – KU Leuven, ESAT/Light & Lighting Laboratory

1. Motivation, specific objective

Spatial brightness plays an important role in the experience of indoor lighting. How to balance between brightness and energy saving is a challenge for interior lighting design. Nowadays, regulations mostly use illuminance to quantify the amount of light. However, illuminance is not enough to predict the brightness perception of a room. As far as we know, there is no clear model to predict spatial brightness of rooms since there are so many diverse features in different rooms, including lamp positions, light-intensity-distribution of lamps, colour of lamps, room shape, wall and object colour, etc.
With the aim of developing a model, this research focusses on identifying valid experimental indicators for estimating room brightness. This paper reports on the results of an indicator based on the concept of “brilliance”. Brilliance is related to the appearance mode of stimuli and how its changes from a black object, to a clearly reflective objective (containing some grey), to a fluorent object (no grey content visible in object) to finally a self-luminous object as its luminance changes. The luminance thresholds at which appearance switches mode could be used as estimators for room brightness, since immediate surround and observer adaptation state will also impact these threshold levels.

2. Methods

In this pilot study, spatial room brightness will be investigated in a room for 2 correlated colour temperatures and at 3 illuminance levels and 3 kinds of spotlight patterns. According to these 18 different interior lighting conditions, observer magnitude responses of room brightness perception B will be collected by asking them to draw a mark on a scale. After estimating the room brightness directly, observers will have to adjust the luminance of different translucent spheres located at different room positions until those spheres reach a critical luminance which make them appear just self-luminous (defined as GL in brilliant research) and which make them appear just reflective (defined as G0 in brilliant research). Spheres are used in this to equally represent the impact from all directions. The brightness perception B, the critical brilliant luminance values G0 and GL of all testing positions for each room lighting conditions will be statistically analysed.

3. Results and conclusions

Detail results and conclusions will be reported in the full paper. It is hoped that new insights will be gained on which factors drive perceived room brightness and how it is best modelled.