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Controlled Clinical Trial
. 2011 Jan 26;6(1):e16429.
doi: 10.1371/journal.pone.0016429.

Non-visual effects of light on melatonin, alertness and cognitive performance: can blue-enriched light keep us alert?

Sarah Laxhmi Chellappa  1 , Roland Steiner, Peter Blattner, Peter Oelhafen, Thomas Götz, Christian Cajochen
Affiliations
Controlled Clinical Trial

Non-visual effects of light on melatonin, alertness and cognitive performance: can blue-enriched light keep us alert?

Sarah Laxhmi Chellappa et al. PLoS One. .

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.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. Protocol design.
Light exposure at 6500K (blue bar), 2500K (orange bar) and 3000K (yellow bar).
Figure 2
Figure 2. Spectral composition (light wavelength by Irradiance µV2/(cm2x nm) of light at 6500K (blue line), 2500K (orange line) and 3000K (yellow line).
Figure 3
Figure 3. Sleepiness and well-being during pre-light, 2-h light (grey bar) at 6500K, 2500K and 3000K, and post-light.
* p<0.05.
Figure 4
Figure 4. Mental effort, visual well-being and glare/brightness during pre-light, 2-h light (grey bar) at 6500K, 2500K and 3000K, and post-light.
* p<0.05.
Figure 5
Figure 5. Distribution of RT, PVT median RT, PVT fastest RT and GO/NOGO RT during pre-light, 2-h light (grey bar) at 6500K, 2500K and 3000K.
* p<0.05.
Figure 6
Figure 6. Salivary melatonin during pre-light, 2-h light (grey bar) at 6500K, 2500K and 3000K, and post-light.
* p<0.05.
Figure 7
Figure 7. Correlations between salivary melatonin and PVT RT and GO/NOGO RT for light at 6500K, 2500K and 3000K.
See this image and copyright information in PMC

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