Energy efficient lighting through glare control
Glary light causes the eye's pupils to contract, thereby preventing part of the light from reaching the retina. The lighting becomes ineffective physiologically. The project will identify and disseminate the real relationship between the eye's reaction and glare conditions (correlation with common calculation methods), and promote energy savings through lighting design that reduces glary conditions.
The more we can avoid glare, the more light reaches the retina, because the pupil size is proportional to the sensation of glare.
Traditionally in Denmark, we have been more preoccupied with glare than elsewhere in the world. Unfortunately, poorly shielded luminaires (e.g. some LED-based) are more energy efficient than luminaires that protect against glare, because the light is not absorbed in the interaction with the luminaire materials. But maybe only if energy efficiency is measured in W/m2.
The project aims to find the optimum balance between glare and energy consumption. M.Sc., Ph.D. Kai Sørensen, who has more than 40 years of experience, has estimated that at least 30% of Europe's energy consumption for street lighting could be saved if the glare conditions were optimal and the eyes got full advantage of the light. Something similar probably applies indoors, but the real connection between glare estimations (expressed as the known calculation indices UGR and DGP) and the retina's supply of light needs clarification.
The project results will be disseminated and applied in two stages:
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Recommendations for reduction of glare throughout Denmark aimed at lighting professional and architects, since it is expected that light levels can be adjusted down if glare is reduced.
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As a powerful stimulus for a large-scale, international, standardization preparatory research project to form new, physiology-based efficiency and glare metrics.
This is the outputs from the project “348- 009 “Energy efficient lighting through glare control” supported by ELFORSK. An abundance of light in a given environment causes the eye's pupils to constrict. This project hypothesises that glary light causes the pupils to constrict excessively, thereby preventing part of the light from reaching the retina. The lighting becomes ineffective physiologically.
Through several pilot tests and a large experiment comprising 16 participants, the project has identified and disseminated a novel description of the relationship between the eye's reactions (pupil areas and gaze directions) in various office-like glare conditions. It has been shown, that indeed some excessive pupil constriction appears, and that up to 4% light may be saved in ordinary office environments alone through careful design. Further, the project has produced some other unexpected, but important findings:
1) Pupil constriction is not (as hypothesized) governed by glare conditions as expressed in the UGR formula, but is strongly correlated simply to the vertical illuminance level measured at the eye. This leads to the conclusion that pupil constriction is just a minor part of the impact that glaring light produces in the visual system and that the mechannisms responsible for the perception of discomfort glare are likely to be found in retinal reactions or in the nervous system including brain processes.
2) The use of wallwashers that reduced contrast in the field of vision greatly affected the pupil constriction stability, which may be an important visual comfort metric.
3) There are great individual differences in both pupil reactions and gaze reactions to the simple and rather ordinary lighting scenes presented to the participants.
It should be noted also that a former research program (ELFORSK 346-046 –2016) dealing with the exploration of preferences in energy efficient indoor lighting showed that wall luminance played a significant role in general brightness of a space. The electric power of new generations of wall washers, counting for about 0.3 to 1,0 W/m2 in typical rooms can often be compensated by reduction of the same power of general lighting, or even more for large spaces.
Dissemination
The results of the project at hand have been communicated in an article for the magazine LYS (to be published 1st December 2017), and through the newsletters of Danish Lighting Center and Danish Lighting Innovation Network. Further, the report will be accessible through the webpage of the Danish Lighting Center. A scientific paper based on the present study will be presented to the international magazine Lighting Research and Technology in 2018. A theme day on glare based on the project results and allowing for more expert input, as well as practical implementation guidelines, is planned for the autumn of 2017. The project was financed by ELFORSK and the contributing partners.
Key figures
Category
Participants
| Partner | Subsidy | Auto financing |
|---|---|---|
| Aalborg Universitet (Fredrik Bajers Vej) | ||
| Aarhus Universitet | ||
| Region Hovedstaden |
