title: Non-visual effects of light on melatonin, alertness and cognitive performance: can blue-enriched light keep us alert?
abstract: BACKGROUND
  Light exposure can cascade numerous effects on the human circadian process via the non-imaging forming system, whose spectral relevance is highest in the short-wavelength range. Here we investigated if commercially available compact fluorescent lamps with different colour temperatures can impact on alertness and cognitive performance.
  
  
  METHODS
  Sixteen healthy young men were studied in a balanced cross-over design with light exposure of 3 different light settings (compact fluorescent lamps with light of 40 lux at 6500K and at 2500K and incandescent lamps of 40 lux at 3000K) during 2 h in the evening.
  
  
  RESULTS
  Exposure to light at 6500K induced greater melatonin suppression, together with enhanced subjective alertness, well-being and visual comfort. With respect to cognitive performance, light at 6500K led to significantly faster reaction times in tasks associated with sustained attention (Psychomotor Vigilance and GO/NOGO Task), but not in tasks associated with executive function (Paced Visual Serial Addition Task). This cognitive improvement was strongly related with attenuated salivary melatonin levels, particularly for the light condition at 6500K.
  
  
  CONCLUSIONS
  Our findings suggest that the sensitivity of the human alerting and cognitive response to polychromatic light at levels as low as 40 lux, is blue-shifted relative to the three-cone visual photopic system. Thus, the selection of commercially available compact fluorescent lights with different colour temperatures significantly impacts on circadian physiology and cognitive performance at home and in the workplace.
authors.affiliation: Centre for Chronobiology, Psychiatric Hospital of the University of Basel, Basel, Switzerland.
authors.forename: Sarah Laxhmi
authors.initials: SL
authors.lastname: Chellappa
authors.forename: Roland
authors.initials: R
authors.lastname: Steiner
authors.forename: Peter
authors.initials: P
authors.lastname: Blattner
authors.forename: Peter
authors.initials: P
authors.lastname: Oelhafen
authors.forename: Thomas
authors.initials: T
authors.lastname: Götz
authors.forename: Christian
authors.initials: C
authors.lastname: Cajochen
mesh_terms: D002940:Circadian Rhythm / Q000528:radiation effects; D003071:Cognition / Q000528:radiation effects*; D003116:Color; D018592:Cross-Over Studies; D005453:Fluorescence; D006801:Humans; D008027:Light; D008297:Male; D008550:Melatonin / Q000528:radiation effects*; D011930:Reaction Time / Q000528:radiation effects*; D055815:Young Adult
chemical_list: D008550:Melatonin