At which wavelength (in nm) is the rod-cone break absent due to equal sensitivity of photopic and scotopic systems?

The phenomenon of the rod-cone break refers to the point at which the sensitivity of the rod photoreceptors (scotopic vision) and the cone photoreceptors (photopic vision) diverge as light intensity increases. In general, rod sensitivity dominates in low light conditions, while cone sensitivity becomes more pronounced in bright light conditions.

At approximately 650 nm, the sensitivity of the cones is still significant, and the rods begin to lose their dominance in terms of visual perception. This wavelength is in the red region of the spectrum, where the cones (particularly the long-wavelength sensitive L-cones) exhibit a greater sensitivity. Therefore, at this point, the contribution of both photoreceptor systems is quite balanced, leading to the absence of the rod-cone break.

On the other hand, at wavelengths such as 500 nm and 580 nm, the differences in sensitivity between the rod and cone systems become more pronounced, resulting in a distinct rod-cone break. At 740 nm, even more so, the sensitivity leans toward the cone system significantly, indicating that the rod function has largely diminished.

Thus, the absence of the rod-cone break at 650 nm stems from the equal contributions of both photoreceptors to