How our phones lie to us

 

For many of us, a screen is the first thing we see in the morning and the last thing we look at before we go to sleep. Yet, for all the time we spend with our beloved devices, how much do we really know about them? What secrets are they hiding?

Let’s talk about how our phones lie to us…

The big lie

The screens of most modern devices use an RGB display. This means the screens are composed of a grid of tiny units called pixels, each containing red, green, and blue-coloured sub-pixels.

When we zoom in on an RGB display, we see a grid of pixels made up of red, green and blue sub-pixels – Image by Anthea Hull

Although each sub-pixel can only produce light of its respective colour, we obviously don’t see just red, green and blue light when we look at our phones. So, what’s going on? How do our phones trick us into seeing colours that aren’t really there?

To answer this, we need to talk about colour.

Colours uncovered

Visible light is a form of radiation, called electromagnetic radiation, which exhibits different properties depending on its wavelength. High energy forms of electromagnetic radiation, like X-rays, have short wavelengths. Low energy forms, like radio waves or microwaves (yes, the kind you reheat your food with), have long wavelengths.

Most forms of electromagnetic radiation are, thankfully, invisible to us – just imagine how chaotic the world would appear if we could see the waves emitted by every mobile phone and radio tower. The reason visible light alone is, well, visible, is because the cells in our eyes exclusively detect a narrow band of wavelengths in the middle of the electromagnetic spectrum. These are the wavelengths of the visible spectrum.

Electromagnetic spectrum – Image by Anthea Hull

Humans eyes contain three types of colour-detecting cells. While each cell type is most sensitive to a specific wavelength, a single wavelength usually triggers more than one cell. In fact, it’s the specific combination of cells, and how strongly they’re triggered by a wavelength, that allows us to distinguish one colour from another.

The colours from the visible spectrum are known as spectral colours, meaning that they are each produced by a single wavelength. As this is the case for the red, green and blue colours produced by RGB sub-pixels, these too are considered spectral,

Not everything is what it seems

The wacky thing is that humans can perceive a single colour for a bunch of different reasons.

To perceive a spectral colour, a single wavelength must stimulate a specific combination of cells in our eyes. However, the same colour can also be created if our eyes detect a combination of different wavelengths, so long as they collectively stimulate our eyes in the same way as the spectral colour.

It’s like paint. Say you want to paint something green – You can either buy green paint from a shop, or you can mix blue and yellow paint together. If you get the ratios just right, you’ll get the same colour either way.

In the case of RGB displays, combinations of colours are used to mimic the way spectral colours trigger the cells in our eyes. Each sub-pixel of an RGB display can appear fully dark, fully bright, or anywhere in between. This means that when activated in the correct combinations, with the correct intensity, the red, green and blue sub-pixels trick us into perceiving an entire range of colours.

If the red and green sub-pixels are fully lit, for example, we perceive yellow. If the green and blue sub-pixels are at full intensity, they create cyan. Add more red and the cyan becomes paler, reduce the intensity of the green and blue to make it appear darker.

If you’re interested, you can find a great interactive tool to experiment with RGB colours at http://www.cknuckles.com/rgbsliders.html.

A little white lie?

RGB displays represent a fascinating intersection between technology and biology, where the quirks of human vision are exploited to trick us into seeing colours that aren’t really there. Although our phones are lying to us, perhaps that’s not necessarily a bad thing. Call me shallow, but I’d take a lying phone with a beautiful RGB display over a honest black-and-white brick phone any day.

 

 


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