Martine Knoop

A study on overhead glare in office lighting conditions

High-intensity light sources illuminating the human eye may create discomfort glare, or at higher intensities even disability glare. In many office lighting conditions, light from overhead luminaires in the ceiling may deliver stray light into human eyes, and as such create discomfort glare, generally referred to as overhead glare. In this paper, overhead glare for a LED luminaire comprising amatrix array of small LED sources using subjective evaluation methodologies and theoretical models, commonly accepted to evaluate glare, were investigated. The perceived overhead glare of the LED luminaire is evaluated at various luminance levels and at different angles (i.e., between 55 and 90°) with respect to the line of sight of the viewer. The results show that a luminaire comprising a matrix of high-intensity point sources can cause overhead glare and can become glary at lower averaged luminance levels than a luminaire with a uniform light source even at high evaluation angles with respect to the line of sight of the viewer. In addition, the conventional UGR model for predicting discomfort glare needs adaptation for a reliable prediction of perceived overhead glare of complex LED luminaires consisting of a matrix of small-sized high-intensity light sources.

Colored Lighting in Offices the New Caffeine? Looking into Performance Effects of Colored Lighting

Innovations in lighting technology have made it simple to realize a wide range of lighting colors, and effortlessly change settings when desired. According to popular belief, color and lighting influence mood, well-being and performance. However, research is inconclusive regarding such claims; often variables such as brightness are not well controlled, or only subjective and no performance measures are reported. This study aims to address some of these issues. In an office setting, one wall was illuminated with blue or red light with comparable saturation and brightness. These colors were chosen because of inconclusive views on their effect, and their potential relevance for office-tasks. White light was offered in the immediate task-area, to meet illuminance and color rendering requirements. 76 participants were randomly assigned to one condition, and asked to perform several tasks. Mixed effects were found of condition on task performance.

Opinion: Studies on non-image-forming effects – Lighting cold cases?:

A cold case is a criminal case that remains unsolved but one which new investigative techniques may make it possible to solve. In order for this to occur, a detailed documentation of existing evidence and the circumstances in which it was collected is required. I believe this applies to studies of the non-image-forming (NIF) effects of light as well. Presently, there is a lack of any clear pattern in these findings, especially for studies conducted during daytime. Some of these studies can be considered as lighting cold cases! This research field is new, and over the course of the last decade, specific lighting characteristics, previously not considered in detail, have been found to be of importance. One example: In 2013, an interdisciplinary group of researchers concluded that rods, cones and intrinsically photosensitive retinal ganglion cells can all contribute to NIF effects, although it is still unclear to what extent. Following the publication of their statement, most NIF studies have included the spectral power distribution (SPD) of the light sources in the description of offered lighting condition. A future investigative technique addressing the contribution of the various retinal receptors can only be applied to those ‘lighting cold cases’ that have properly documented SPDs. In my opinion, we neglect to document at least one additional relevant lighting variable at present. Even though the scientific basis is small, some research indicates that the area of the retina illuminated also matters. In inducing some NIF effects, inferior or nasal retinal light exposure is said to be more effective than light falling on the superior or temporal side of the retina. In addition, binocular light exposure seems to produce a higher melatonin suppression than monocular light exposure. The commonly used vertical illuminance or melanopic weighted irradiance, both integral measurements, are not appropriate characteristics. They do not provide information about the area of the retina illuminated. Nonetheless, when we conduct NIF experiments in a mock-up room or field study, instead of in an integrating sphere, both the origin of the light and its SPD can be essential lighting characteristics. For a white room, with identical SPDs for all light sources, one luminance image might be adequate additional documentation; situations with different SPDs from different directions require a more elaborate specification. I invite the lighting community to discuss and define a common description of the retinal irradiance pattern so as to allow a detailed analysis of data in the future! And the retinal irradiance pattern is not the only important variable that needs to be recorded. Investigating NIF responses is a complex research topic that requires a similar detailed consideration and documentation of all other possible influencing variables, such as timing and duration of exposure, light history and chronotype. This is not possible without expert knowledge from different disciplines. NIF studies benefit greatly from cooperation between chronobiologists, environmental psychologists and lighting engineers. It is our combined task to prepare and document interdisciplinary NIF studies properly to ensure that rather than a cold case they become a case solved.