Both short wavelength (blue) light and caffeine have been studied for their alerting effects on humans. The ability of blue light to enhance alertness, mood and cognitive function via non-image forming neuropathways has been suggested as a non-pharmacological countermeasure for drowsiness across a range of occupational, medical, educational and military settings. Despite this fact, this was the first study to compare blue light and caffeine, and to examine any interaction effects. Thus, the aim of the study was to test the effects of blue light/placebo (BLU), white light/240 mg caffeine (CAF), blue light/240 mg caffeine (BCAF) and white light/placebo (PLA), on alertness and mood. A randomised, controlled, crossover design study was used, in a student population of 21 healthy volunteers. The participants rated their mood on the Swedish Core Affect Scales (SCAS) and their alertness was assessed by the Karolinska Sleepiness scale (KSS) and a reaction time test, prior to and after each experimental condition. The caffeine conditions decreased subjective sleepiness compared to the non-caffeine/white light condition on the KSS. Plain blue light produced an alerting effect, compared to non-caffeine/white light condition measured by the reaction time test. The combination of blue light and caffeine had a medium to large positive effect on mood. The effects of the combination of blue light and caffeine need to be further investigated, and the possibility of a hyper-arousal effect cannot be ruled out.