Spectrophotometry is the science of measuring the light-absorbing and light-transmitting characteristics of a substance. Many substances absorb light and transmit light of specific wavelengths within the ultraviolet (200 - 400 nm), visible (400 - 700 nm) and near-infrared (700 - 1000 nm) regions of the electromagnetic spectrum. These light-absorbing / light-transmitting characteristics of a substance are useful in determining the presence and concentration of that substance in a sample.