This paper was a first attempt to investigate how variations in experimental design affect the conclusions drawn about lamp spectrum and spatial brightness. The topics included procedure, evaluation mode, visual task, and field size. The analyses are made by comparing results from past studies and these tended to be insufficient to draw robust conclusions. The conclusion stated “It is found that further work is needed to enable this comparison.” Further work has indeed been conducted and this is shown in other papers in these lists.
The main recommendations include:
- to counterbalance all options (left-right positions in a side-by-side matching test)
- to observe independent variables (e.g. light settings) in a randomised order
- to include null condition trials to enable internal validation
- to use multiple procedures to test the same set of stimuli
- to describe an experiment in sufficient detail to enable others to repeat the work
- to analyse the results using suitable statistical methods.
CIE report 212:2014. Guidance towards best practice in psychophysical procedures used when measuring relative spatial brightness. Commission Internationale De L’Éclairage, Vienna, 2014. ISBN 978-3-902842-51-0
A literature review was conducted to identify studies investigating the effect of illuminance and CCT on pleasing (or preferred) lighting and brightness. Only those studies meeting the requirements of CIE212:2014 were retained.
The results of these studies demonstrated that:
- Variation in CCT has negligible effect on ratings of brightness and pleasantness.
- Low illuminances (less than approximately 300 lux) may be perceived as unpleasant; an illuminance of 500 lux is sufficient to provide a pleasant environment and further increase in illuminance above 500 lux is of little benefit.
- Higher illuminances are perceived to be brighter and this effect appears to be stronger than for other relationships.
A discussion of research methods, whether planning new work or reviewing published work by others. This paper looks at research quality considerations, research design, internal and external validity, defining lighting conditions, statistical analysis and research ethics.