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Creating illusions with primary colours

07 Mar 2016  | John Dunn

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Television screens and some outdoor advertisements are built as a matrix of picture elements where each picture element consists of a trio of three separate colour sources that deliver emissions of what we call the "primary colours." Those primary colours are green, red, and blue.

This is not the same definition of primary colours which applies to a surface that is illuminated by white light for which the "primary" colours are yellow, red, and blue, but that's a whole different story. Also, please note that we are not addressing another LED approach, a quite different technology, which delivers just white light from what are perceived to be white light sources like this:

When the green, red, and blue trio of light emitting sources are activated at varying intensities, our eyes mix those emissions and we obtain the illusion of being able to see all the other colours. Thus, when you think you're seeing yellow, orange, violet, brown, and so forth, you are really responding to some combination of the trio of green, red, and blue light sources.

This being an optical illusion not withstanding, it's a very useful visual effect as we know so well from watching colour television.

I have noticed on some Times Square movie theatre marquees that when I come up close enough, I can visually pick out the three separate colours. The illusion does have its limits.

About the author
John Dunn contributed this article.

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