Mixing Light
Red, green, blue — and why an apple needs red light to be red
What this lesson covers
Why it matters
Your TV has never owned a yellow lamp. Every yellow you've ever seen on a screen was red and green light, mixed right under your nose.
Predict first
Shine a RED and a GREEN spotlight on the same white wall. The patch where they overlap looks…
Light adds: red + green = YELLOW, green + blue = cyan, red + blue = magenta, all three = WHITE. (Paints work the other way — they SUBTRACT.)
- yellow — coloured lights ADD up — correct
- muddy brown, like mixing paints
- it stays red — red is stronger
What you do
Switch the three lamps: build yellow, then white — then turn off red and watch the red apple lose its colour.
Check yourself
The primary colours of LIGHT are…
RGB — every screen you own builds its millions of colours from just these three lamps.
All three primary lights together make…
Adding all of light's colours rebuilds white — the reverse of the prism splitting it.
A red apple in pure GREEN light looks…
An object's colour is the light it REFLECTS. The apple reflects only red — offer it none, and it has nothing to show you.
- red, green and blue — correct
- red, yellow and blue
- black and white
- white — correct
- black
- brown
- black — there is no red light for it to reflect — correct
- red as always
- green