Bright Light, an Effective Fatigue Countermeasure

clip bright light


Turn on and turn up the light to reduce fatigue and improve performance. Studies have shown that bright light as low as 750 to 1,000 lux can increase alertness and help you get through your night shift[1]. Most of the research has looked at the ability of constant bright light to suppress melatonin and trick your brain into thinking it is daytime and time to be awake, alert and performing well.

But there is a movement in fatigue research to use light in shorter bursts to temporarily relieve fatigue and improve performance without suppressing melatonin. The strategy is called a fatigue countermeasure. The term “countermeasure” refers to strategies that are aimed at reducing fatigue that manifests during critical operations. This use of the term is consistent with the military origin of the term where an action is taken to reduce an imminent threat; for example, launching a decoy or flare to distract a missile is considered a military countermeasure.

But there is a movement in fatigue research to use light in shorter bursts to temporarily relieve fatigue and improve performance without suppressing melatonin. The strategy is called a fatigue countermeasure. The term “countermeasure” refers to strategies that are aimed at reducing fatigue that manifests during critical operations. This use of the term is consistent with the military origin of the term where an action is taken to reduce an imminent threat; for example, launching a decoy or flare to distract a missile is considered a military countermeasure.

The bright light fatigue countermeasure procedure goes something like this…when you are fatigued or preferably, at the time that you have calculated that you will likely be fatigued[2], you turn on a bright light unit. The unit should be close enough for your eyes to pick up at least 750 to 1,000 lux of light indirectly. You don’t have to stare at the light, but it should be focussed on your eyes. The light should have the wavelength band of 470 to 480 nm filtered out so that melatonin won’t be suppressed if you are using this countermeasure during your normal night time. This will reduce the risk of long term negative health consequences and still allow the bright light to counteract the fatigue. If it is your normal daytime, you don’t have to worry about filtering out the 470 to 480 nm. Melatonin is normally suppressed during daytime. If you can continue operating in the bright light, then you do so. If you cannot, then the question becomes, “how much operational time can a short dose of light yield?”

Answering this question will take some time. The research still needs to be completed and it is a complex question to answer. Preliminary work suggests that the required dose of filtered light depends on many factors such as age, prior light exposure, circadian phase and wavelengths of light. There does however, appear to be a dose response curve and measurable effects from even a short dose of light[3]. This means that the relationship is likely not 1 to 1. It is more likely that one minute of bright light results in more than one minute of improved alertness and performance.


Footnotes:

[1] See for example: Campbell, S., & Dawson, D. (1990). Enhancement of nighttime alertness and performance with bright ambient light. Physiology and Behaviour, 48(2), 317-320.

[2] It is difficult to know when you are actually fatigued, people normally underestimate fatigue and overestimate performance. If you wait until you think you are fatigued, it might be too late. It is better to use fatigue risk factors like continuous wakefulness, acute sleep disruption, chronic sleep disruption and circadian rhythm effects to predict your fatigue risk period and then use your countermeasure at that time.

[3] As little as one minute of 2,000 lux bright light may have measurable effects, see for example: Hayashi, M., Masuda, A., Hori, T. (2003). The alerting effects of caffeine, bright light and face washing after a short daytime nap. Clinical Neurophysiology, 114(12), 2268-2278.