Question

Do you think that the light that reaches the detector should be less than, the same, or more than the light that enters the sample? Explain your answer.

Answer 1

A spectrophotometer is employed to measure the amount of light that a sample absorbs. The instrument operates by passing a beam of light through a sample and measuring the intensity of light reaching a detector.spectrophotometer readings are usually reported as absorbance, the instruments actually measure optical density. In the simplest terms, optical density (OD) has the same definition as absorbance:

OD = log( I_o / I)

However, optical density result from any process that decreases the light intensity reaching the detector, and therefore has a variety of causes in addition to the quantum mechanical absorbance phenomenon. One major cause of optical density is light scattering, by either particles or gas bubbles that are present in the sample. Another major cause of optical density is the sample cuvette.

Due to Stray Light
All Monochrometers have a small bit of stray light getting out If you assume that this stray light is not at the wavelength being absorbed, then it will represent a small amount of light that reaches the detector that should not, so the absorbance of the light is lower than expected. This effect gets worse as the concentration of the sample increases, because more and more light is getting absorbed by the sample and the small amount of scattered light
becomes more and more significant.

The scattered light is probably from the most intense light output of the source, and is also probably at a wavelength that the detector is more sensitive to. Hence the scattered light becomes an even larger portion of what that detector sees.

Hence light that reaches the detector sould be more than the light that enters the sample.