I've made a very simple colorimeter. An RGB LED illuminates transparent liquid samples with red, then green, then blue light. A detector detects the intensity of light that comes through the liquid.

I put blue food coloring into water and tested it. I was surprised that it seemed that blue light was NOT transmitted but the other two colors were, with red transmitting the most.

I'm fairly sure I'm interpreting my results correctly, but they are very much contrary to my expectation. Do my results make sense? If so, why?


1 Answer 1


It "reflects" (actually scatters). Transmission of blue is lower.

  • $\begingroup$ Note that colour behaviour of some compound materials can be far from simple, e.g. en.wikipedia.org/wiki/Lycurgus_Cup $\endgroup$
    – dominecf
    Apr 27, 2020 at 9:03
  • $\begingroup$ For example, air is blue. If you look at the white Sun through a long air column, as at dusk, the blue light has been preferentially scattered into other people's daytime skies, and the sunlight which reaches you is reddish. $\endgroup$
    – rob
    Apr 27, 2020 at 9:03

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