The discussion centers around the question of why humans cannot see ultraviolet (UV) light. It explores the biological and environmental factors that influence human vision, particularly in relation to the spectrum of light emitted by the sun and the adaptations of the human eye.
Participants generally agree on the biological adaptations of the human eye and the environmental factors affecting UV visibility, but the discussion remains open regarding the implications of these factors and the extent to which they influence human vision.
The discussion does not resolve the complexities of UV light's interaction with human vision, including the role of atmospheric absorption and the evolutionary advantages of sensitivity to visible light over UV light.
The sun is a strong source of ultraviolet radiation, but atmospheric absorption eliminates most of the shorter wavelengths. The eyes are quite susceptible to damage from ultraviolet radiation. Welders must wear protective eye shields because of the uv content of welding arcs can inflame the eyes. Snow-blindness is another example of uv inflamation; the snow reflects uv while most other substances absorb it strongly.