Effect of Correlated Color Temperature and S/P-ratio of LED Light Sources on Reaction Time in Off-axis Vision and Mesopic Lighting Levels

• Published in: Leukos Vol. 19; no. 1; pp. 4 - 15
• Main Authors: Vicente, E. G., Matesanz, B. M., Rodríguez-Rosa, M., Sáez, A. M., Mar, S., Arranz, I.
• Format: Journal Article
• Language: English
• Published: New York Taylor & Francis 02.01.2023; Taylor & Francis Ltd
• Subjects: Color temperature; Cones; correlated color temperature; Correlation; Excitation spectra; Illumination; LED; Light emitting diodes; Light sources; mesopic; night driving; Parameter sensitivity; Reaction time; Rods; S/P-ratio; Sensory stimulation; spectral power distribution; Spectral sensitivity; Temperature; Time measurement; Vision; Visual effects; Visual tasks
• ISSN: 1550-2724; 1550-2716
• DOI: 10.1080/15502724.2021.1970580

The increasing replacement of traditional lamps by LED technology opens the door to research into visual performance under their multiple possible spectral power distributions. The correlated color temperature and S/P-ratio are considered parameters characterizing the spectrum of a light source. The lack of firm conclusions motivates the analysis in this work of the influence of LED spectrum, which is defined by the correlated color temperature and S/P-ratio, on a representative night-driving task, visual reaction time. A two-channel and four primaries photostimulator was used as set-up for measuring reaction time in off-axis vision, at mesopic illumination conditions and for a range of stimulus contrasts. The experimental conditions included a wide range of correlated color temperatures, ranging from 1870 to 6350 K, and different S/P-ratios for the same temperature. A total of 16 young subjects participated in the experiments. The results show significant shorter reaction times for those conditions in which the spectrum has greater short-wavelength content. This is corroborated by the greater stimulation of rods and S-cones obtained in the calculation of their excitation level. However, the definition of the spectrum using the correlated color temperature and S/P-ratio does not equally define the results obtained. For the same temperature, a higher S/P-ratio provides lower reaction time values, but for the same S/P ratio reaction time is independent of the temperature. LED light sources with high short-wavelength content provide faster response on the basis of a greater excitation of rods and S-cones. The S/P-ratio is the best parameter to justify the effect of spectrum on reaction time, as considers the spectral sensitivity of the visual system in its calculation.