Original: The visual sensitivity of a human being is from about 4,000 ångströms (violet) to 7,000 ångströms (dark red) so the use of the ångström as a unit provided a fair amount of discrimination without resort to fractional units.
Simplified: The visual sensitivity of a human being is from about 4,000 Ångstroms (violet) to 7,000 Ångstroms (deep red) so the use of the ångström as a unit provided a fair amount of discrimination without resort to fractional units.