Light's ability to increase alertness is strongest at very short wavelengths

Subjective alertness levels were significantly higher in 420 nm light compared to 470 nm and significantly lower in 600 nm light.

• A range of non-image-forming light responses in humans is sensitive to short wavelengths between 440-480 nm.
• Healthy male subjects were exposed to light pulses of 420, 440, 470, and 600 nm to assess their effect on alertness.
• The study included 12 participants, with subjective mood and alertness measured using 9-point scales over 4-hour exposure periods.
• Duration of light exposure had a significant impact on alertness, indicating that longer exposure may enhance alertness levels.
• Results indicate that subjective alertness may be maximally sensitive to very short wavelength light, particularly at 420 nm.

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