Thorbjörn Laike

The impact of flicker from fluorescent lighting on well-being, performance and physiological arousal

In working environments all over the world, fluorescent tubes are by far the dominating light source. Still, there have been very few studies on the impact of the non-visible flicker from fluorescent tubes. The purpose of the study was to compare the impact on subjective well-being, performance and physiological arousal of fluorescent light powered by conventional and high-frequency ballasts. Thirty-seven healthy males and females were subjected to either condition in a laboratory office on two separate occasions with 1 week in between. Although the methodology was quite extensive, only a few general effects were observed. However, when the light was powered by the conventional ballasts, individuals with high critical flicker fusion frequency (CFF) responded with a pronounced attenuation of EEG alpha waves, and an increase in speed and decrease in accuracy of performance. These results may be understood in terms of heightened arousal in the central nervous system in response to the pronounced light modulation caused by the conventional ballasts. In order to alleviate this potential stress source, it is recommended that fluorescent lighting be powered by electronic high-frequency ballasts of good quality.

Residents' perceptions following retrofitting of residential area outdoor lighting with LEDs

The use of light emitting diodes (LEDs) in outdoor lighting has energy-saving potential, but users’ responses to this light source are largely unknown. An intervention study in two residential areas compared conventional lighting installations (high pressure sodium in Area 1 and high pressure mercury in Area 2) to a retrofitted LED-alternative regarding residents’ perceptions of quality of light, visual accessibility and danger. Moreover, energy use was calculated. Residents’ (N = 60) visual accessibility improved and perceived danger remained low in both areas after retrofitting. In Area 2 the perceived quality of light increased, whereas in Area 1 the results were mixed. The retrofitted application reduced energy use by 41–76% and might be a feasible alternative to conventional outdoor lighting in relatively safe areas.

Psychic Changes following Myelography with Metrizamide and Iohexol : A comparative investigation with psychologic tests

Based upon the results of repeated psychologic tests, psychic impairment following myelography has been studied in 60 patients. Thirty of these had lumbar myelography with metrizamide and 30 with iohexol. Psychic impairment was noted in both groups, although with a higher frequency and much more marked in the group which had metrizamide myelography. For this type of examination iohexol is thus to be recommended.

The impact of daycare environments on children's mood and behavior

This study examined the influence of different environmental features at nine daycare centers on 74 childrens (42 boys and 32 girls) emotions in relation to their individual traits. The environments were predominantly assessed by semantic scales, and the childrens emotions using a structured observational technique. Hierarchical regression analysis revealed that the activation level as well as the control of the behavior were related to the individual traits of the children, whereas the directedness and the hedonic tone of the behavior were related to the environment and the situation (meal or free play). Of special interest is the result that extrovert children displayed higher levels of control than the more introvert children. The most important quality of the physical daycare environment was unity, whereas intensity and familiarity were to most salient qualities of the social environment.

Daylight harvesting control systems design recommendations based on a literature review

In indoor spaces, lighting control systems are highly effective to reduce electric lighting use. Daylight harvesting systems (DHS) promise to deliver the greatest energy savings. This article presents a review about DHS based on recent scientific and technical literature. The review shows that the energy saving potential of DHS lies between 20-60% in comparison with non-dimmed installations. However, many studies outline serious limitations of these systems such as e.g. limited user acceptance. The review suggests that, during the design and commissioning of a DHS, the following aspects deserve attention: technical robustness, architectural integration and human acceptance. The review concludes that, while further research in the technical area is still needed, the architectural and human aspects have been so far insufficiently studied. The review emphasizes that competent designers and installers, as well as post-commissioning are mandatory to ensure the success of DHS installations.

A field study of fluorescent and LED classroom lighting

Indoor lighting is facing a massive retrofit to LED lighting. Research is needed to assess whether LED-based lighting can promote energy efficiency, boost visual comfort and support biological functions. This field study considered the lighting of four identical classrooms in an upper secondary school in Helsingborg, Sweden. Two classrooms were fitted with state-of-the-art ceiling pendants containing T5 fluorescent tubes and that had a direct/indirect light distribution (the control rooms). The other two classrooms were fitted with an experimental LED indirect lighting system (the experimental rooms). In the classrooms, 72 students aged 17–18 years performed their usual educational activities over a whole academic year. The light environment, electricity consumption, and students’ mood, light perception and saliva cortisol concentration were monitored. The two lighting systems produced only marginal differences. Overall, the experimental rooms were slightly preferred but achieved only small energy savings due to high parasitic losses.

Optimal office lighting use : A Swedish case study

Purpose – The purpose of this paper is to determine the optimal office lighting use with different types of lighting controls to achieve energy savings and provide visual comfort for individuals. Design/methodology/approach – A case study and field measurements were carried out in 18 single-occupancy offices in Sweden where six different lighting controls were investigated. Occupancy and daylight hours were key issues for determining the lighting use. For each office, occupancy patterns, use of a ceiling luminaire, energy usage and perceptions of office lighting in the spring-summer and autumn-winter were established. Findings – The use of luminaires varied among the occupants and could be habitual. Though the study yielded positive results concerning the potential for manual or daylight dimming with occupancy switch-off controls to increase optimal lighting use, combining dimming controls with manual on/off controls is rather effective if occupants generally sit in their offices most of the day. Research...

Psychologic Tests in the Evaluation of Psychic Changes after Myelography with Metrizamide

The possibility of using psychologic tests to demonstrate psychic changes following myelography with metrizamide was investigated in 15 patients. The tests were made before and after the examination. The results revealed psychic changes of cognitive nature to occur both at 6 and at 24 hours after myelography. Of the tests used determination of the reaction time gave most significant results. Subjectively the patients considered themselves better 24 hours after the examination than after 6 hours. This was not confirmed from the test results—an observation indicating the sensitivity of the test instruments used. Thus, these appear to be well suited to study cognitive changes caused by the contrast media used in this particular type of examination. Since the tests are repeatedly performed, the effect of habituation and of learning cannot be avoided. However, when applied in groups of patients, in whom the effects of different contrast media are compared, the disadvantages of these specific effects can be neglected.

Comparison of Static and Ambulatory Measurements of Illuminance and Spectral Composition That Can Be Used for Assessing Light Exposure in Real Working Environments

ABSTRACT Reliable measurements are of utmost importance when investigating the relationship between light and human reactions. The aim of the present study was to compare two methods for measuring light exposure in real working environments. Ambulatory recordings of illuminance and irradiance were compared with static field measurements of horizontal illuminance at the normal working position, average horizontal illuminance in the room, vertical illuminance at the position of the eye in the normal angle of gaze, and spectral composition of the light radiation at the normal working position and at the position of the eye in the normal angle of gaze. The ambulatory measurements were carried out during a 3-day experimental period and were repeated monthly throughout the year. The static field measurements in the subjects’ offices were conducted five times during the year, in the morning and afternoon during one day. The relationship between the illuminances and irradiances measured with the portable instruments and the static measurements was statistically analyzed. Results from the analyses revealed that more than one third of the static measurements of vertical illuminances recorded were below 200 lx, and only 7% of the measurements exceeded 1000 lx. Measurements of the spectral composition of the light radiation in the rooms suggested that the light, although at a fairly low intensity, included relatively much radiation that can have a non-image forming effect. Furthermore, only a small number of significant correlations between the ambulatory and static measurements were found. Results from the t-tests showed that there were no differences between ambulatory measurements, and static measurements of horizontal illuminance at the normal position, average illuminance in the room and vertical illuminance at the position of the eye during three, five, and seven of the 10 measurements, respectively. There is a need to define appropriate parameters in order to describe the quality of a lit environment with respect to the non-image-forming effects of light radiation.

Seasonal Variation in Bright Daylight Exposure, Mood and Behavior among a Group of Office Workers in Sweden

The purpose of the study was to investigate seasonal variation in mood and behavior among a group of office workers in Sweden (56°N). Thirty subjects participated in this longitudinal study. The subjects kept a weekly log that included questionnaires for ratings of psychological wellbeing and daily sleep-activity diaries where they also noted time spent outdoors. The lighting conditions in the offices were subjectively evaluated during one day, five times over the year. There was a seasonal variation in positive affect and in sleep-activity behavior. Across the year, there was a large variation in the total time spent outdoors in daylight. The subjects reported seasonal variation concerning the pleasantness, variation and strength of the light in the offices and regarding the visibility in the rooms. Finally, the subjects spent most of their time indoors, relying on artificial lighting, which demonstrates the importance of the lighting quality in indoor environments.