Blue light (BL, short wavelength, ca. 480 nm) is known to influence circadian rhythm system, alertness, cognitive and affective functioning of humans (see e.g. Fisk et al., 2018). In this experiment we limited the BL exposure to approximately 10%, by providing the participants with amber contact lenses – to be used continuously during four weeks. Every week of BL blockade, neural, biochemical and psychological variables were registered. Here we present the results of actigraphy, subjective daytime sleepiness assessments, and biological assays of saliva samples. The aim of the study was to assess the influence of prolonged BL blockade on sleepiness-alertness in young individuals. One can assume that wearing amber lenses imitates, to some extent, natural ageing process in the eye, i.e. yellowing of the lenses (it is estimated that the transmission of blue light – at 480 nm – decreases by 72% from the age of 10 to 80 years – Kessel et al., 2010). It may be hypothesised that reduced BL stimulation would result in lowered general alertness and lesser suppression of melatonin secretion, that is, its higher levels and earlier onset time. Two mechanisms may be considered: (1) lack of blue light in the evening earlier DLMO and higher levels of melatonin earlier and better sleep improved general well-being, and/or (2) lack of BL during the day lack of triggering effect sleepiness, lowered mood and energy worsened general well-being.