The Effects of Timed Exposure to Light Therapy: A Fatigue Countermeasure

Primary Investigators:
Kristena M. Kons & Lauren Fowler, Ph.D.
Weber State University, National Science Foundation


  1. The use of light therapy will adjust the circulating melatonin levels affecting participants’ circadian rhythms so as to phase advance on the morning/day shifts and phase delay on the swing shift.
  2. Greater improvement in cognitive performance will occur in the morning/day shifts than in the swing shift with the use of light therapy.


  1. 11 US Air Force air traffic controllers and 2 weapons controllers were tested over 4 shifts and 4 testing sessions using: a) with and without the Feel Bright Light bright light device; b) salivary melatonin tests; c) the ANAM Synthetic Work Task to test multi-tasking performance similar to job requirements.
  2. Participants were on rapidly-rotating 5 day/week work schedules:
    – mornings (07:00-16:00 hours)
    – days (08:00-17:00 hours)
    – swings (15:00-23:00 hours)
  3. Melatonin data were collected early in the week and also at the beginning of the day & morning shifts (7:00-8:00 hours) and at the end of the swing shifts (21:00-22:00 hours).
  4. Fatigue measures were collected before and after bright light treatment.


  1. Use of the bright light prior to the work shift had a significant effect by shift -on physiological fatigue (p<.05). Melatonin levels were significantly suppressed during the swing shift, not the morning/day shifts.
  2. Multi-tasking scores almost doubled with bright light treatment prior to the morning/day shifts (p<.01).

The Effects of Timed Exposure to Light Therapy Graph


  1. Bright light treatment resulted in improved cognitive performance.
  2. The findings demonstrate the feasibility of using an inexpensive and portable bright light device to reduce fatigue-related errors.