Visual performance under CMH and HPS lighting systems: NumeLiTe project final report

Outdoor lighting, especially for roadways, is one of the most important areas of power consumption as well as being an important safety issue. Any reduction in the energy used by lighting therefore needs to be controlled without compromising road safety. A three-year research project, NNE5-2001-0082, entitled "An integrated approach to designing high intensity discharge lighting systems", part-sponsored by the European Commission, aimed to prove the feasibility of an optimal and energy efficient outdoor lighting scheme for urban illumination. Six European countries: France, Germany, Greece, Portugal, Switzerland and the United Kingdom were consortium partners in the project. The part of the work carried out at TRL was jointly sponsored by the European Commission, the UK Department for Transport (DfT), and the UK County Surveyors Society (CSS). A primary issue to be addressed was whether whiter light has advantages in visual perception terms compared to the light spectrum, of yellow appearance, from conventional lamps and, if so, can it be produced economically with low energy consumption. The vision of the human eye at low (mesopic) light levels and possible efficiency gains in the lamp, luminaire optics and the control gear have therefore being investigated. The first phase of the work at TRL was an international literature review of vision and outdoor lighting research which comments on the effectiveness of the visual system in road user tasks at these low light levels. The second phase comprised laboratory work carried out by TRL which is also described in this report. This involved assessment of the comparative reflective properties of relevant road surfacing materials under "conventional" and "prototype" light sources. The samples which were tested were from the trial road at TRL and one of the roads in the trial in Albi, France. Also included was a sample of a negatively textured "thin" surfacing, which had been trafficked on the TRL road machine. The measurements were taken in a specially built rig at TRL. Measurements were made on all three of the samples while dry and the TRL and Albi surfaces when wet. The results showed that there was no measurable change in the spectrum of the light from either source on reflection by any of the surfaces and allowed calculation of the specularity factors (S1) and estimates of the average luminance coefficients Q0to be made. In the third and final phase of the work at TRL full-scale trials were performed. These included observations designed to measure, separately, the responses of road users' central and peripheral vision. The trial made use of three male and three female observers covering a wide age range. One test compared the reaction times of the observers in CMH and HPS light, full and dimmed to approximately half power to a change of luminance of a peripheral visual target. In the other test the observers were asked, while driving a vehicle, to detect a 200mm diameter spherical target placed on the road ahead in one of 6 positions, under the same four lighting conditions. The distances at which the target was detected were then recorded. In the peripheral visual observations, the time taken for each observer to detect a change of luminance in a peripheral target, was measured. The results showed that, for the luminance conditions assessed, there was no significant difference between peripheral reaction times or target detection distances under the different lighting systems, either at full-power or dimmed. (A)