When flashblindness occurs, people are unable to see what is going on around them or what they are doing.

A 6 kiloton blast could cause flashblindness 0.5 miles (0.8 km) away on a clear day, or 20 miles (32 km) away at night.

Many people in Hiroshima and Nagasaki were blinded for several minutes. Some cases of flashblindness lasted up to three hours, and one person suffered permanent blindness.

A nighttime blast probably would have caused more severe blinding effects due to the degree of pupil enlargement and focusing actions of the eye.