Which Wavelength of Light is Beneficial for eyes?

Most of the studies that point to beneficial effects use LEDs as the light source with the vast majority around the wavelength of 670nm (red light). Wavelength and light type/source are not the only important factors though, as the light intensity and exposure time affect the results.

Blue, violet and UV light wavelengths (200nm-480nm) are bad for the eyes, being linked to either retinal damage or damage in the cornea, humour, lens and optical nerve. This includes direct blue light, but also blue light as part of white lights such as household/street LED bulbs or computer/phone screens. Bright white lights, especially those with a high colour temperature (3000k+), have a large percentage of blue light and are not healthy for the eyes. Sunlight, especially midday sunlight being reflected off water, also contains a high percentage of blue, leading to eye damage over time. Luckily the earth’s atmosphere filters out (scatters) blue light to some extent – a process termed ‘rayleigh scattering’ – but midday sunlight still has a lot, as does sunlight in space seen by astronauts. Water absorbs red light more so than blue light, so the reflection of sunlight off lakes/oceans/etc is just a more concentrated source of blue. It’s not just reflected sunlight that can do harm though, as ‘surfer’s eye’ is a common issue related to UV light eye damage. Hikers, hunters and other outdoorsmen can develop this. Traditional sailors such as old navy officers and pirates would almost always develop vision issues after a few years, mainly due to sea-sunlight reflections, exacerbated by the nutritional issues. Far infrared wavelengths (and just heat in general) can be harmful for the eyes, as like with other cells of the body, functional damage occurs once the cells get too warm (46°C+ / 115°F+). Workers in old furnace related jobs such as engine management and glass blowing always developed eye issues (as the heat radiating from fires/furnaces is far infrared). Laser light is potentially harmful for the eyes, as mentioned above. Something like a blue or UV laser would be the most destructive, but green, yellow, red and near infrared lasers can still potentially cause harm.