Computer and Phone Light Suppresses Sleep (study summary)

Because light exposure can affect circadian rhythm, researches wanted to know if lamp type (fluorescent and incandescent) and light temperature (kelvin) had different effects upon circadian rhythm, motor skills and cognitive skills.

1. During 2-hour exposure to light in the evening, CF lamp with light at 6500K will attenuate the expression endogenous melatonin levels, in comparison to light at 2500K and at 3000K;

2. CF lamp with light at 6500K will promote an augmentation of subjective and objective alertness levels when compared to light at 2500K and at 3000K during and after 2-hour exposure to light in the evening. Furthermore, it will have an overall effect of enhancing alertness and performance in cognitive tasks specifically associated with sustained attention.

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Three subject groups received light exposure for 2 hours in the evening.

The light does were:

• 40 lux at 6500K compact fluorescent
• 40 lux at 2500K compact fluorescent
• 40 lux at 3000k incandescent

After exposure, researchers tested the subjects’ cognitive and motor skills.

Researchers found that the 6500 K blue light suppressed melatonin. Subjects reported feeling more alert. While they felt well and were visually comfortable, they had significant decreases in their reaction times. This is a counter-intuitive result.  The light exposure did not affect their cognitive performance.

6500K closely matches sunlight color temperature. Our brains react to sunlight with suppressed melatonin so that we are alert during the day.

In this study, 40 lux at 6500K did suppress melatonin, but 40 lux at 2500K did not. Both light sources were compact fluorescent.

The 300K incandescent exposure did not significantly suppress melatonin.

Avoid 6500K light exposure at night to prevent its negative effect on sleep cycles.