I am not a native speaker, nor do I know the proper grammatical name of this kind of words to look up this question. So please excuse the possible duplication or simplicity. But as far as I know, the words mentioned in the subject cannot be used in plural, although they have a grammatical plural form. So you don't say
These two parts have different reflectances.
This document describe radiations reflected from different parts of the machine.
but rather reflectance and radiation.
- Am I correct?
- What is the proper explanation for this? I need to tell it to a colleague.
- How can one determine if this rule applies to a specific word or not, besides the gut feeling?
Best Answer
"Reflectance", like other measurable quantities like "speed" and "area", may be used as countable or uncountable. So
(could be "speeds", but "speed" is more natural, at least to me).
but
"Radiation", not being a measurement, does not pattern this way. It is usually uncountable (so does not take a plural). Like most uncountable nouns it can be used as countable when it refers to different kinds of radiation, but I don't think that this use is very common.
but
(but "kinds of radiation" would be more natural there).
So, in answer to your question
is fine, but "reflectance" would be OK as well.
This would be unusual, especially if the radiation from the different parts was all of the same kind. (I guess "part" was just an error).