Why backing material matters in colorimeter reflectance mode

[xp2334]

Homework Statement

1) What considerations should be taken when interpreting the results of color measured by transmission and reflectance mood for clear/translucent fluids?
2) What possible effects the room lighting has on the results obtained for transparent/translucent/opaque samples measured in reflectance mode?

Relevant Equations

no calculations involved

qns 1 attempt:
In reflectance mode, measurements are taken based on the amount of light reflected from the surface of the sample. Therefore, in clear/translucent fluids, it is critical to have appropriate backing material behind the sample, such as a white and matte piece of paper or cardboard, or else the results may be compromised.

For transmittance mode, the width of the cuvette used will impact the path length of light which impacts the amount of light absorbed. Thus, the type of cell used during the experiment should be taken into consideration when interpreting the results measured.

qns 2 attempt:
For translucent/clear samples, ambient light is reflected and may therefore impact the readings whereas, for opaque samples, the light gets absorbed and therefore isn't reflected.

 

[haruspex]

In reflectance mode, measurements are taken based on the amount of light reflected from the surface of the sample. Therefore, in clear/translucent fluids, it is critical to have appropriate backing material behind the sample, such as a white and matte piece of paper or cardboard, or else the results may be compromised.

if you have a white background some of the light you are observing has come through the fluid, so you are mixing reflected light with transmitted.