The Influence of Lighting Conditions on Mood, Alertness, and Subjective Wellbeing in Non-Clinical Populations

The last twenty years have seen increasing research on what is known as the non-visual function of the eye. It is established that intrinsically photosensitive retinal ganglion cells send signals to the central part of the brain and influence various body functions such as body temperature and hormone release. Much work is concerned with the effect of exposure to light in the evening on sleep (and subsequent effects on health) and on so-called bright-light therapy which morning exposure to light can be used to treat seasonal-affective disorder. However, this thesis is concerned with the effect of early-morning exposure to light of non-clinical populations and explores the hypothesis that such exposure could benefit subjective wellbeing.

The work described uses various methods to evaluate the effect of light including subjective questionnaires, measurement of ear temperature, and measurement of brain response (EEG). The effect of correlated colour temperature (CCT) of light was evaluated; light with CCT between 5000-8000K generally had a positive effect on emotions and alertness but at higher CCTs the effect was much less or even negative for some measures. In general, some evidence was found that early morning exposure to light can be beneficial in terms of wellbeing in non-clinical populations.

The mode of light delivery was also investigated and frontal exposure, although having some positive effects, can sometimes be uncomfortable. On the other hand, exposure to light behind the head and even through the In-ear can also have some potential benefits and is less likely to cause side effects (such as headaches). In the final part of the thesis subjective wellbeing was explicitly investigated and a model that connects subjective wellbeing with other measures such as PANAS (a subjective questionnaire which is used in many studies) and KSS (a questionnaire that measures sleepiness) was developed.

This work has contributed to our understanding of how lighting of different correlated colour temperature can affect human emotional and wellbeing response. It has implications to the design of lighting in homes, office and public spaces and suggests that lighting has a functional role to play in addition to its aesthetic properties.