## Additive Colour Mixing – Pixels

### Experiment number : 2261

• #### Goal of Experiment

This experiment helps students to understand the way in which displays of mobile phones, tablets, computers or televisions (e.g. LCD or OLED technology) create individual colours.

• #### Equipment

USB microscope, mobile phone display (or tablet, laptop, etc.)

• #### Theory

The colour screens of digital devices around us are made up from so-called pixels. Each pixel consists of three parts – subpixels – which each emits only one colour: red, green and blue. The resulting colour perception that our eye acquires is created due to a so-called additive mixing model of these three colours; this colour model is known by the abbreviation RGB.

The desired colour shade depends on how intense is the light emitted by each individual subpixel. For example, if blue and red subpixels shine at the same time, the eye will evaluate this composition as a purple colour, while its shade will be more “red” or “blue” given by the intensity of red and blue light.

From a technological point of view, individual subpixels in OLED screens are the sources of coloured light, in the case of LCD screens the situation is more complicated. LCD screens are backlit with white light, the intensity of which is determined in each subpixel by rotation of liquid crystals; the colour of the subpixel is then given by a colour filter.

• #### Procedure

1. Using MS Paint, MS Word or another similar tool, prepare several squares of different colours on your computer or tablet screen – red, blue, yellow, white, etc.

2. Run the program that operates the USB microscope.

3. Place the microscope close to the monitor and focus it so that the pixels are not blurred.

4. Examine what the individual colours look like under the microscope.

• #### Sample Result

Red, yellow, blue, white and purple area on a laptop screen observed by a USB microscope. It is obvious that, for example, yellow is created by combining red and green, white is a combination of all three subpixels.

• #### Technical Notes

• Install and test the program that operates the USB microscope beforehand.

• Place the microscope on the monitor surface carefully to avoid scratching the screen.

• USB microscopes are usually equipped with dimmable diodes that illuminate the zoomed object. For this experiment, it is advisable to turn off the diodes completely to avoid reflection from the glossy (but also matte) surface of the screen.

• #### Pedagogical Notes

It may be interesting to point out to students that different shades of red look different under a microscope. At the same time, it can be shown that if you set the proportion of the G (green) and B (blue) components on the RGB colour palette to zero, only the red pixels will actually remain lit.

• #### Related Experiments

Pixels can also be studied quantitatively using a USB microscope, as described in Measuring the Size of a Pixel experiment.