Understanding light
Light & colour
Everything in Photonica starts from one idea: light is a wave, and its colour is its wavelength. Get comfortable with that and the rest of optics falls into place.
Colour is a length
Visible light is an electromagnetic wave with a wavelength between roughly 380 nm (violet) and 750 nm (deep red). A nanometre is a millionth of a millimetre, so about two thousand waves of green light fit across a human hair.
| Colour | Wavelength | Where you meet it |
|---|---|---|
| Violet | 380–450 nm | The far edge of the rainbow; blacklights sit just beyond |
| Blue | 450–495 nm | The sky; the 486 nm hydrogen F line used in lens design |
| Green | 495–570 nm | Where your eye is most sensitive; 532 nm laser pointers |
| Yellow | 570–590 nm | Sodium street lamps; the 587.6 nm d line, the reference for glass |
| Orange / red | 590–750 nm | Sunsets; 632.8 nm helium-neon lasers; the 656 nm C line |
White is a mixture
White is not a wavelength — it is what your eye reports when many wavelengths arrive together. That is why a prism can "split" white light: there was never one colour there to begin with. The light source in Photonica offers three spectra:
| Spectrum | What it traces | Use it for |
|---|---|---|
| Mono | A single wavelength you choose | Lasers, clean measurements, wave experiments |
| RGB | Three wavelengths: 640, 532 and 450 nm | Seeing colour separation quickly and cheaply |
| White | 24 wavelengths spread across the visible range | Rainbows, dispersion, photoreal renders |
How colour gets drawn
Each ray is traced at its own wavelength and then converted to a screen colour for display. A 532 nm ray is drawn green because 532 nm looks green, not because anything in the simulation is labelled "green". When rays overlap, their light adds — which is why the middle of a dispersed fan goes white again where all the colours still coincide.
Brightness versus power
Two separate things control how light looks:
- Power (mW) is physical. It sets what the detector reads in milliwatts and W/cm², and it is what you change if you care about the measurement.
- Brightness and Laser power in the Photo panel are display gains. They change how bright the render looks and nothing else.