What wavelength is red light?

Red light occupies the wavelength range of approximately 620 to 750 nanometers (nm) in the visible electromagnetic spectrum. This corresponds to a frequency range of 400–484 THz and a photon energy of 1.65–2.00 eV.

Why does red light scatter less than other colors?

Red light scatters less due to Rayleigh scattering, where scattering intensity is proportional to 1/λ⁴ (one over wavelength to the fourth power). Because red has a longer wavelength than blue or green, it scatters far less in the atmosphere. This is why sunsets appear red and why red warning lights are visible through fog.

Why do sunsets appear red?

At sunrise and sunset, sunlight travels a longer path through the atmosphere. The shorter blue and green wavelengths scatter away via Rayleigh scattering (proportional to 1/λ⁴), leaving the longer red and orange wavelengths to reach the observer directly, producing the characteristic red-orange sky.

Optics & Perception of Red

Q: How is red produced in modern display technology?

Modern displays use several approaches: OLED displays use organic electroluminescent compounds that emit red light when electrically excited. Quantum dot displays use precisely-sized cadmium selenide nanocrystals (CdSe) that emit pure red at exact wavelengths due to quantum confinement. The Rec. 2020 color space standard pushes red primaries to 630 nm for maximum color gamut.

Red occupies the longest-wavelength end of the visible spectrum, spanning approximately 620 to 750 nanometers. Of the three types of cone photoreceptors in the human retina, L-cones (long-wavelength sensitive) peak near 564 nm but extend their sensitivity well into the red range, allowing us to perceive these wavelengths as the vivid color we call red. This physiological sensitivity is not accidental — it evolved to help primates detect ripe fruit against green foliage.

Red light scatters less in the atmosphere than shorter wavelengths, which is why sunsets and sunrises appear red: when sunlight travels a longer path through the atmosphere at low angles, blue and green wavelengths are scattered away, leaving red and orange to dominate the sky. This same principle makes red ideal for warning signals — red light penetrates fog and haze more effectively than blue or green.

In display technology, red has undergone a revolution. Early CRT monitors used europium- doped yttrium oxide phosphors to produce red. Modern OLED displays achieve red through organic electroluminescent compounds, while quantum dot displays use precisely-sized cadmium selenide nanocrystals to emit pure, saturated red at exact wavelengths. The Rec. 2020 color space standard pushes red primaries to 630 nm, demanding ever-purer red sources from display manufacturers.

Key Physical Properties

Wavelength range: 620–750 nm
Frequency: 400–484 THz
Photon energy: 1.65–2.00 eV
Rayleigh scattering: Minimal (1/λ⁴ dependency favors longer wavelengths)
Photoreceptor peak: L-cones at ~564 nm, extended sensitivity to 700+ nm

Optics & Perception of Red

Key Physical Properties

Frequently Asked Questions