What is the wavelength range of visible light?

Human vision spans roughly 380 to 750 nanometres. Violet sits at the short end near 380–450 nm, and red at the long end near 625–750 nm. Wavelengths below 380 nm are ultraviolet and above 750 nm are infrared, both invisible to the eye.

How do I convert wavelength to frequency?

Use f = c/λ, where c is the speed of light (about 2.998×10⁸ m/s) and λ the wavelength in metres. For 550 nm green light, f = 2.998×10⁸ / 550×10⁻⁹ ≈ 5.45×10¹⁴ Hz, or about 545 THz. Shorter wavelengths give higher frequencies.

Why does red have a lower frequency than violet?

Frequency and wavelength are inversely related through c = λ·f. Red light has the longest visible wavelength, so it has the lowest frequency and the least energy per photon. Violet has the shortest wavelength and therefore the highest frequency and energy.

Are the colour boundaries exact?

No. Colour perception is continuous and varies between people and lighting, so the nanometre ranges for each colour are approximate conventions. Different sources draw the violet–blue or yellow–orange line a few nanometres apart, and there is no sharp boundary in the spectrum itself.

Where do the colours of a rainbow come from?

A rainbow forms when sunlight refracts and reflects inside water droplets. Because refractive index varies slightly with wavelength, each colour bends by a different amount and separates out — violet bends most, red least — spreading white light into the visible spectrum you see as bands.

Visible Light Wavelength Reference

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Visible light is the narrow band of the electromagnetic spectrum the human eye can see, from violet at about 380 nm to red at about 750 nm. This reference maps each colour to its wavelength and frequency range and includes a lookup that names the colour for any wavelength and computes its frequency.

How it works

Each colour corresponds to a band of wavelengths, measured in nanometres (billionths of a metre). To find the frequency, use the wave equation:

f = c / λ

where c ≈ 2.998×10⁸ m/s and λ is the wavelength in metres. Because the speed of light is fixed, frequency rises as wavelength falls. Violet light, with the shortest visible wavelength, has the highest frequency (around 670 THz), while red light, with the longest wavelength, has the lowest (around 430 THz).

Reading the spectrum

The order from short to long wavelength is violet, blue, cyan, green, yellow, orange, red — the familiar rainbow sequence reversed depends only on whether you list by wavelength or by the order you see them refracted. Green sits in the middle near 550 nm, where human eyes are most sensitive in daylight, which is why safety and high-visibility gear often uses yellow-green.

Example and notes

A 633 nm helium-neon laser glows red: the tool places it in the red band and computes a frequency of about 474 THz. The colour boundaries here are approximate conventions — colour perception is continuous, and different references draw the lines a few nanometres apart, so treat the ranges as guides rather than exact cut-offs. Values just outside 380–750 nm are flagged as ultraviolet or infrared.