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GCSE level Physics exam revision notes on colour
Visible spectrum and colour: Part 5.
Colour and how the eye and TV screens
work (RGB systems)
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 INDEX of physics my notes: The
visible spectrum and colour of objects
5. The eye and TV screens
(from a physics point of view)
The eye and the brain work together when
see light from objects viewed around us.
Different rods and cone cells at the back of
the eye in the retina can detect red, green and blue light photons.
All
these visible light photons have sufficient energy to trigger a tiny
electrical impulse that goes to the brain from photosensitive protein
molecules.
When all three types of cell (RGB
cones) are triggered we see white, but each type of cone detects mainly red,
green or blue photons.
Combinations of the cell responses create
signals to the brain which it interprets into all the colours of the visible we see
- violet, indigo, blue, green, yellow, orange and lots of shades in
between!
and, things are even more complicated
than that.
e.g. yellow light is detected by
both red and green cones, so you don't really see a pure yellow
colour.
For more on the
structure and
function of the eye (school biology notes)
Infrared photons do not have enough
energy to trigger a response from the retinal cone cells, so we don't
visually detect infrared EM radiation.
Ultraviolet photons have far more
energy than visible light photons and can cause damage from chemical
changes in the retinal cells.
Colour television uses the properties of
primary colours. In an old TV screen there are three electron guns
that hit a sort of paint called a phosphor.
When hit by electrons the
phosphors glow either red, green or blue.
The screen consists of thousands of
pixels each containing a set of the three phosphors - the RGB system.
By making these three
phosphors glow at different intensities (brightness) they create the
illusion of all the colours you experience when viewing the screen.
Digital cameras and colour printing
also work on the basis of the three primary colours.
Modern digital TV and
computer screens also use an RGB system, but these screens are made up of
tiny
pixels, each containing sub-pixels: one red,
one green, and one blue.
Variation of the intensity
of the digital signal for each sub-pixel, the screen creates millions of colours.
INDEX of my physics notes: The
visible spectrum and colour of objects
Key points for
COLOUR -
RGB system and its applications
Information
sources for Doc Brown's key points: IGCSE-GCSE physics are based on textbooks
& syllabus-specifications for students taking the UK AQA,
Edexcel, OCR 21st Century Science, OCR Gateway science suite, WJEC, CCEA &
CIE GCSE
physics 9-1 level science examinations.
A syllabus-aligned
revision guide on RGB colour mixing, TV screens, and
the human eye, tailored for students preparing for GCSE/IGCSE Physics across
WJEC, CCEA, CIE, AQA,
Edexcel, and OCR:
RGB Colour Model – Additive Colour Mixing
- Primary colours of light:
Red, Green, and Blue
(RGB).
- When combined in different
proportions, they produce all other colours of visible
light.
- Additive mixing:
- Red + Green =
Yellow
- Green + Blue =
Cyan
- Blue + Red =
Magenta
- All three together =
White light
RGB is used when mixing light,
not pigments. Think of screens, not paint!
How TV and Computer Screens Use RGB
- Screens are made up of tiny
pixels, each containing sub-pixels: one red,
one green, and one blue.
- By varying the intensity
of each sub-pixel, the screen creates millions of colours.
- This is how images, videos, and text
appear in full colour.
Real-World Examples:
- Smartphones, tablets, TVs,
monitors all use RGB
pixels.
- LED displays
and projectors also rely on additive colour mixing.
The Human Eye and Colour Perception
- The retina at the
back of the eye contains photoreceptor cells:
- Rods:
Detect brightness (black and white), work well in low light.
- Cones:
Detect colour, work best in bright light.
- Three types of cones:
Red-sensitive, Green-sensitive, and
Blue-sensitive.
- The brain interprets signals from
these cones to perceive colour.
Example:
- When both red and green cones are
stimulated, we perceive yellow.
Tip:
The eye’s cones match the RGB model — that’s why RGB works so well for
screens!
Required Practical Applications
- Use colour filters
and light boxes to explore additive mixing.
- Observe how TV screens
or phone displays show colour under a magnifying glass.
- Investigate how filters
affect the appearance of coloured objects.
Exam Tips for Students
- Use correct terminology:
additive mixing, sub-pixels, photoreceptors, retina, cones.
- Be able to label diagrams
of the eye and RGB pixel structure.
- Understand the difference
between additive (light) and subtractive (pigment)
mixing.
- Practice past paper questions
that ask about colour perception and screen technology.
- Link physics to biology:
explain how the eye detects RGB light and how screens exploit this.
Keywords, phrases and learning objectives for
visible light and RGB colours
Know that the eye and TV/computer screens work on
the mixing of the primary colours red, green and blue (RGB
systems)
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INDEX of physics notes: The
visible spectrum and colour
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Revision notes on how a laptop/TV
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for students taking IGCSE/GCSE level physics examinations, summary
revision notes and key points on how a laptop/TV screen uses the RGB
pixel system for students taking the AQA
igcse/gcse physics notes on how a laptop/TV screen uses the RGB pixel system, Edexcel gcse
physics notes on how a laptop/TV screen uses the RGB pixel system, OCR 21st century GCSE
physics notes on how a laptop/TV screen uses the RGB pixel system, OCR gateway
GCSE physics notes on how a laptop/TV screen uses the RGB pixel
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RGB pixel system, CCEA
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physics, exam revision notes on
how a laptop/TV screen uses the RGB pixel system, useful for US grade 9-10 physics courses,
importance of how the eye processes
light to create colour
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light to create colour for
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INDEX of my physics notes: The
visible spectrum and colour of objects
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