The researcher working in the field of illumination can use a number of measurement methods, depending on the requirement. Many practical evaluation methods employ varieties of a configuration where test stations are positioned next to or opposite each other for comparison purposes. Test stations can consist of test booths or even full-sized test rooms when using indoor evaluations. The number of test booths for indoor application may differ from one to three. Most colour and light perception studies thus depend on human observers to provide some feedback or input. It is the human observer who uses illumination devices and it is important that human response to these products be measured. Results achieved from these measurements can, in turn, be used by the lighting designer to optimize the design of illumination products. Many studies in the field of colour perception and/or matching rely on the method of “psychophysics” where humans are used. Reliability of results achieved when using human observers can be questioned. Results achieved with psychometric testing cannot be compared with an established benchmark and/or standard as such a benchmark was itself generated using human observers, endangering the researchers to become entangled in a closed circle of cause and effect where one depends on the other. This study investigated the reliability of human observers when studying colour perception. Repeatability of results achieved when using human observers was measured. A test was repeated using the same set of observers. Even this approach is not safe as human memory may serve the observer so well, that results can be selected, or at least influenced, on the basis of memory and not perception. The solution was to implement extended time between measurements, thereby hoping that sufficient time will lapse to erase details from the observer’s memory. A colour matching task had to be completed to test observers of two distinct age groups. One group was older than 50 years of age and the second group was younger than 40 years of age. The two groups were tasked to complete the same colour matching test at the beginning of a year and after one year. Test procedures and test equipment were identical before and after the year.
Psychophysical colour matching, LED, test booth, chromaticity coordinates, age, colour rendering
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