Color vision with a two-photon infrared RGB display.

Human vision is considered limited to the visible range (∼400-700 nm), yet studies have shown that near-infrared light can elicit visual perception through a nonlinear process known as two-photon vision. This occurs when two infrared photons are absorbed simultaneously by photopigments in the photoreceptors, generating a response equivalent to that of a single visible photon. While this phenomenon has been investigated for monochromatic stimuli, its potential for color perception remains unexplored. Here, we present the first functional prototype of a two-photon infrared RGB display and demonstrate that polychromatic color perception can be achieved by using infrared light alone. We have demonstrated that color mixing in this spectral range follows additive principles similar to those of visible light, enabling the perception of a wide gamut of hues, including white. These findings open new avenues for leveraging this alternative visual mechanism in practical applications requiring precise color control, such as immersive display technologies.