Ásta Logadóttir

Investigating the use of an adjustment task to set the preferred illuminance in a workplace environment

An experiment was carried out to examine user preferences for light level using the method of adjustment. The study sought preferred illuminances under lighting from fluorescent lamps of different correlated colour temperature. It was hypothesised that the preferred illuminance would be influenced by variables inherent in the experimental design including the available stimulus range, the anchor (initial setting before adjustment) and adaptation time before onset of adjustment action. The experiment included three different stimulus ranges (21–482 lux, 38–906 lux and 72–1307 lux) and these lead to significantly different preferred illuminances (337 lux, 523 lux and 645 lux, respectively). The experimental results confirmed that stimulus range and anchor have significant effects on the outcome of the adjustment task, confirming the importance of considering and reporting these variables when determining user preference with this method.

Concentrations of Formaldehyde in new Danish Residential Buildings in Relation to WHO Recommendations and CEN Requirements

It is uncertain if current Danish legislation regarding emission of formaldehyde from wood-based panels could assure that concentrations of formaldehyde in the indoor air of buildings containing the material would meet the World Health Organization (WHO) guideline. This is of particular concern since the recent recognition by International Agency for Research on Cancer that formaldehyde is carcinogenic to humans. Therefore, the purpose of this study was to determine whether residents of newly built Danish residential houses could be exposed to safe levels of formaldehyde. Geometric mean concentration of formaldehyde measured in 20 residential buildings was 0.04 mg m−3. Formaldehyde concentrations in two buildings (10%) exceeded the WHO guideline value. In order to explain the relatively high concentrations, a second phase was performed. The aim was to identify the significant formaldehyde sources and to discuss the source strength in relation to field measurements and WHO guidelines. The results showed wide differences between the materials tested, but all steady-state concentrations were below the European standard requirement for class E1. These measurements formed the basis for model calculations of possible resulting concentrations in residential rooms, suggesting that indoor concentrations above the WHO maximum limit could occur. The calculations applied a worst case scenario with all surfaces covered with materials emitting the maximum permissible amount of formaldehyde show indoor concentrations as high as 0.6 mg m−3.

Lamp spectrum and spatial brightness at photopic levels: A basis for developing a metric

Light sources are available in a variety of spectral power distributions (SPDs) and this affects spatial brightness in a manner not predicted by quantities such as illuminance. Tuning light source SPD to better match the sensitivity of visual perception may allow the same spatial brightness but at lower illuminance with potential reductions in energy consumption. Consideration of experimental design was used to review 70 studies of spatial brightness. Of these, the 19 studies considered to provide credible evidence of SPD effects were used to explore metrics for predicting the effect of SPD but did not provide conclusive evidence of a suitable metric, in part because of incomplete reporting of SPD characteristics. For future work, these data provide an independent database for validating proposed metrics.