Increase in cortisol concentration due to standardized bright and blue light exposure on saliva cortisol in the morning following sleep laboratory.

Research studies on LED light exposure and cortisol are inconsistent and not comparable due to different types of light, exposure times, and sample sizes. Therefore, one hour of standardized exposure LED light at different intensities and the spectral composition during the post-awakening phase at 7:30 were compared. A sample of 23 (Study 1) and 26 (Study 2) healthy males were randomly assigned to: 1) bright white light (414 lux) and 2) dim darkened light (<2 lux) as well as 3) red light (235 lux) and 4) blue light (201 lux) exposure conditions. Results from repeated measures ANOVA confirm that light exposure affects the cortisol concentration. Study 1 revealed an increase in the saliva cortisol concentration after bright light exposure compared to dim light. An increase in the cortisol concentration of blue light compared to red light (Study 2) and dim light was found. This study shows that bright light and blue light affect the cortisol response in contrast to dim light and red light conditions. The HPA axis showed a stimulatory effect by bright versus dim light and different wavelengths of light exposure.Lay summaryThe effects of LED light exposure on the stress hormone cortisol were investigated. The light exposure took place during the hours people would start working at the office. The results showed that after one hour of exposure to bright light or blue light the stress hormones increase in contrast to dim light and red light conditions. Thus, stress hormones can be altered by the types of light people are exposed to.