Light is electromagnetic radiation between 380 and 780 nanometres. Below that, infrared (heat). Above, ultraviolet (sunburn). Everything else in lighting design flows from this one fact. Plus: why some properties of light need waves to explain and others need particles.
Four ideas to carry into the next specification conversation you have.
Same family as radio, microwave, X-ray. Only the wavelength differs. Visible band: 380–780 nm.
Red ~700 nm. Green ~550 nm. Violet ~400 nm. White is a mixture of all visible wavelengths.
Wave model explains reflection and refraction. Particle (photon) model explains the photoelectric effect and LED emission.
UV damages skin and yellows plastic (EP10). IR is heat, what makes incandescent inefficient (73% of power lost as IR).
Wavelengths shown in nanometres (nm) for visible light. The full EM spectrum spans many orders of magnitude.
| Band | Wavelength | What it does |
|---|---|---|
| Radio / TV / radar | 1 cm – 100 km | Communications |
| Microwave | 1 mm – 1 cm | Cooking, Wi-Fi |
| Infrared (IR) | 780 nm – 1 mm | Heat, sensed by skin |
| Visible red | 620 – 780 nm | Long-wave warm light |
| Visible green | 490 – 570 nm | Peak eye sensitivity |
| Visible violet | 380 – 450 nm | Short-wave cool light |
| Ultraviolet (UV) | 10 – 380 nm | Sunburn, sterilisation |
| X-ray / gamma | < 10 nm | Medical imaging, radiation |
Five facts that explain why some lamps look different than others.
James Clerk Maxwell in 1865 showed that light is an electromagnetic wave. The same equations predict radio, microwave, and visible light from the same set of laws, they only differ in wavelength.
Einstein's 1905 paper on the photoelectric effect (which won him the Nobel) showed light is also discrete packets of energy, photons. LEDs emit one photon per electron transition across the p-n junction.
Human evolution optimised vision for the sun's peak output, which falls in this range. Other animals see further into UV (bees) or IR (snakes).
Sunlight is continuous across all visible wavelengths. Low-pressure sodium is monochromatic (589 nm yellow only). White LEDs are blue + phosphor with a yellow dip. The discontinuity is what makes colour rendering hard.
UV-C (200-280 nm) sterilises water. IR penetrates skin and warms tissue. Visible light barely affects skin. The same EM family, wildly different biology by wavelength.
Every NLC fixture spec lists the spectral power distribution (SPD), CCT, and CRI, because the physics matters, and we sell to engineers who care.
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