I am an undergraduate researcher using a NanoDrop Lite Spectrophotometer to estimate protein concentrations based on A280 molar extinction coefficients. According to the Beer-Lambert Law,

A = c * l * ϵ

where A is absorbance, c is molar concentration, l is pathlength, and ϵ is the molar extinction coefficient. However, I have been taught that this linear relationship only holds true for absorbance values between 0.1 and 1.0 (some say 1.5), so any sufficiently concentrated sample must be diluted to an absorbance of