As illumination decreases, which wavelengths appear brighter?

The perception of brightness in relation to light wavelengths is closely tied to the human visual system's sensitivity. Under lower illumination conditions, the eye's response to different wavelengths changes, favoring shorter wavelengths, typically in the blue and violet spectrum.

As illumination decreases, the cones, which are responsible for color vision and operate best in bright light, become less effective. Instead, the rod photoreceptors, which are more sensitive under low-light conditions, take over. Rods are more sensitive to shorter wavelengths, particularly around 498 nm (blue-green area of the spectrum). This shift in photoreceptor activity effectively makes shorter wavelengths appear brighter compared to the longer wavelengths when light levels drop.

Understanding this phenomenon highlights the way the human eye adapts to varying light conditions, emphasizing the relative sensitivity of our visual receptors based on environmental illumination.