How many lumens does it take to blind someone?

Eighty lumens is sufficient to cause temporary flash blindness in dark conditions, and 200 lumens can cause temporary blindness in daylight. Visible light is not sufficient to cause permanent blindness, regardless of the intensity.

A concentrated beam such as a high-intensity laser is necessary to induce permanent blindness with visible light. Damage to eyes from sunlight and artificial lamps comes from ultraviolet radiation rather than visible light wavelengths. Infrared radiation can also cause blindness by burning the retina. Radiation higher in frequency than ultraviolet light does not cause direct injury to the eye; it passes through the retina with minimal absorption.