SOURCE AND EFFECT

Three of the most recent Lighting Research and Technology papers focus on the impacts of light in varying contexts both real and virtual, finds Iain Carlile

ee and Lee note that with an

Lincrease in coloured lighting in the built environment, there still exists little empirical research on how people perceive it. They have therefore investigated the effect of coloured lighting on people's pleasure and arousal, and how this may differ with ethnicity.

Using the Mehrabian and Russell’s emotional state model, which measures pleasure, arousal and dominance (PAD), an experiment was conducted to investigate the effect of six lighting colours: red, green, blue, yellow, orange and purple. A controlled laboratory experiment was conducted using a colour-changing LED luminaire and involving 82 participants. Their ages ranged from 19 to 45 years, with an equal mix of male and female, 48 Caucasian and 34 Asian. They were exposed to different coloured lighting states at different illuminance levels to simulate potential different applications. Each participant completed a PAD questionnaire about their emotional states under the coloured lighting.

The results showed significant differences in pleasure and arousal for the six different colours. Ethnicity had significant effects on the impact of lighting colour on pleasure, but not on arousal. Blue was considered the most pleasant colour, being significantly higher than red and purple, with red being the least pleasant. Asians found red and purple significantly less pleasant than all other colours of light and tended to feel less pleasant under red, orange and purple lighting conditions than Caucasians.

Ru et al’s paper examines the acute effects of office illumination on cognitive performance during daytime hours, specifically whether the type of task and level of task difficulty moderate the effect of daytime illuminance on cognitive functioning. An experiment was conducted in a simulated office environment, where 30 participants (mean age 20.46 years +/-1.81, 10 male and 20 female) were exposed to high and low illuminances at the eye (high illuminance of around 1036 lux and low illuminance of around 108 lux) using T8 fluorescent light sources with 6500K CCT (Ra 81). The experiment was conducted during working hours throughout which time the participants were tested on varying difficulties of tasks designed to probe sustained attention, response inhibition, conflict monitoring and working memory. Subjective impressions of mood and sleepiness were also recorded.

The authors found that exposure to high versus low illuminance significantly improved the speed on the response inhibition task, and accuracy and speed in the working memory task. These effects were moderated by task difficulty, showing more pronounced effects for the easy tasks. Subjective sleepiness and negative mood were unaffected by illuminance. No significant effects were observed for the sustained attention and conflict monitoring tasks. The authors conclude that the effect of illuminance on cognitive performance appears to be moderated by the type and difficulty of the task, and cognitive tasks are not necessarily reflected in subjective affective experiences.

A study by Rockcastle et al compares perceptions between a modern immersive head-mounted virtual-reality (VR) display and the real space. An experiment was conducted in which 53 participants took part. The participants viewed either a real space, illuminated with a dimmable LED lighting system, or a virtual representation of the space captured using a high-dynamic-range (HDR) camera. In all 30 participants (11 male, 18 female, one other) viewed the real space while 23 participants (eight male, 15 female) viewed the immersive HDR photographs displayed in the VR head-set. Age was evenly distributed between the groups (around 80 per cent aged 18-33 and 20 per cent aged 34-58). Different lighting conditions were presented to the participants, who rated visual comfort, pleasantness, evenness, contrast and glare.

The results were similar when they evaluated well-lit scenes, but significant differences were observed under dim and highly contrasted lighting scenes. This suggests that virtual reality can be a reasonable surrogate for subjective analysis of realworld lit environments when evaluating well-lit scenes. However, it may not provide an adequate medium for dimly lit or highly contrasted scenes.

Iain Carlile, FSLL, is a past president of the SLL and a senior associate at dpa lighting consultants

Lighting Research and Technology: OnlineFirst

In advance of being published in the print version of Lighting Research and Technology (LR&T), all papers accepted for publishing are available online. SLL members can gain access to these papers via the SLL website (www.sll.org.uk)

Effects of coloured lighting on pleasure and arousal in relation to cultural differences

H Lee and E Lee

Diurnal effects of illuminance on performance: Exploring the moderating role of cognitive domain and task difficulty

T Ru, KCHJ Smolders, Q Chen, G Zhou and YAW de Kort

Comparing perceptions of a dimmable LED lighting system between a real space and a virtual reality display

S Rockcastle, M Danell, E Calabrese, G Sollom-Brotherton, A Mahic, K Van Den Wymelenberg and R Davis