The visible spectrum of light is the part of the electromagnetic spectrum that the human eye can detect. It contains the colors we commonly describe as violet, blue, green, yellow, orange, and red.

A commonly used approximate range for visible light is 380 to 700 nanometers (nm), although the exact boundaries are not sharp and can vary somewhat depending on the reference and viewing conditions.

Visible Light Wavelength Range

Visible light is only a very small portion of the complete electromagnetic spectrum.

A useful approximate breakdown is:

These ranges are approximate because colors transition gradually rather than having perfectly defined boundaries.

The basic sequence is:

380 nm → Violet → Blue → Green → Yellow → Orange → Red → 700 nm

What Is a Wavelength?

Light behaves as electromagnetic radiation, and wavelength describes the distance between repeating points of a wave.

It is commonly measured in nanometers for visible light.

One nanometer is:

1 nm = 0.000000001 meter = 10⁻⁹ m

Shorter wavelengths are found toward the violet/blue end of the visible spectrum, while longer wavelengths are found toward the orange/red end.

Violet Light

Violet occupies the shortest-wavelength region of visible light, approximately 380–450 nm.

Near the lower end of this range, visible violet approaches ultraviolet radiation.

Common violet LED wavelengths include approximately:

405 nm / 410 nm / 420 nm

405nm LEDs are often described as violet or violet-blue rather than conventional blue.

Blue Light

Blue light generally occupies approximately 450–495 nm.

Important LED wavelengths include:

450 nm — Royal Blue
455 nm — Royal Blue
460 nm — Blue
470 nm — Blue

450nm is especially important in LED technology. It is commonly used in horticultural lighting and as the blue pump wavelength in many phosphor-converted white LEDs.

Green Light

Green light occupies approximately 495–570 nm.

Typical green LED wavelengths include:

520 nm / 525 nm / 530 nm / 535 nm

The human visual system is highly sensitive in the green region under daylight-adapted conditions, with the photopic luminosity function peaking around 555 nm.

This is one reason optical power and perceived brightness should not be treated as the same thing.

Yellow Light

Yellow light occupies approximately 570–590 nm.

Yellow and yellow-green wavelengths can be used in indicators, signage, decorative lighting and specialty applications.

The transition between green, yellow and amber is gradual, so terminology can vary between LED manufacturers.

Orange and Amber Light

Orange is approximately 590–620 nm, although LED terminology often distinguishes amber from orange.

Common examples include:

590–595 nm — Amber

600–610 nm — Orange

Amber LEDs are used in signaling, automotive applications, decorative lighting and specialty outdoor lighting.

Red Light

Red occupies the longest-wavelength portion of the visible spectrum, approximately 620–700 nm.

Common LED wavelengths include:

620–630 nm — Red

660 nm — Deep Red

660nm is especially important for horticultural lighting and is also used in certain photobiomodulation devices.

Beyond the visible red region are longer wavelengths such as 730nm far-red and near-infrared wavelengths such as 810nm, 850nm and 940nm.

What Comes Before and After Visible Light?

Visible light is positioned between ultraviolet and infrared radiation.

A simplified electromagnetic spectrum is:

Ultraviolet → Visible Light → Infrared

In terms of wavelength:

UV < Visible < IR

For LED applications, a simplified representation could be:

365nm UV-A → 405nm Violet → 450nm Blue → 525nm Green → 590nm Amber → 630nm Red → 660nm Deep Red → 730nm Far Red → 850nm NIR → 940nm IR

Not all of these wavelengths are visible.

Is 365nm Visible?

365nm is UV-A, so it is outside the conventional visible spectrum.

The violet or bluish glow people sometimes observe around UV equipment can arise from visible emissions, fluorescence of nearby materials, or spectral characteristics of the source rather than 365nm itself being conventional visible light.

Is 405nm Visible?

Yes. 405nm is generally visible, although it is close to the violet boundary.

It normally appears violet or blue-violet.

This is why 395nm and 405nm LEDs can look significantly different even though their wavelengths are separated by only 10nm.

Is 450nm Visible?

Yes.

450nm is clearly visible and is generally described as royal blue.

It is one of the most important wavelengths in LED lighting because blue LED dies around this region can be combined with phosphor materials to produce white light.

Is 660nm Visible?

Yes.

660nm is visible as deep red, although the human eye is much less sensitive to 660nm than to wavelengths around the green region.

Consequently, two LEDs producing the same radiant power at 555nm and 660nm would not appear equally bright.

Is 730nm Visible?

730nm is normally categorized as far-red and lies beyond the conventional 380–700nm visible-light definition.

However, the human eye's response does not suddenly become zero at exactly 700nm. Under suitable conditions, some people may detect very deep red light beyond 700nm.

For practical LED engineering, 730nm is usually treated as far-red rather than conventional visible light.

Is 850nm Visible?

No. 850nm is near-infrared (NIR) and is outside normal human vision.

Some high-power 850nm emitters can appear to have a faint red glow, but this should not be used to judge their infrared optical power.

850nm is widely used for:

• Night vision

• Security cameras

• Machine vision

• Sensors

• Infrared illumination

• Some photobiomodulation equipment

Wavelength and Frequency

Wavelength and frequency are related by:

c = λf

where:

c = speed of light
λ = wavelength
f = frequency

As wavelength becomes shorter, frequency becomes higher.

Therefore:

Violet → shorter wavelength, higher frequency

Red → longer wavelength, lower frequency

Wavelength and Photon Energy

Photon energy is also related to wavelength:

E = hc / λ

This means shorter-wavelength photons carry more energy than longer-wavelength photons.

For example, a 450nm blue photon has more energy than a 660nm red photon.

However, this does not mean a blue LED automatically consumes more electrical power or produces more optical power. Those characteristics depend on the LED design and operating conditions.

How Do White LEDs Relate to the Visible Spectrum?

A white LED does not normally produce just one wavelength.

Many white LEDs use a blue LED die, often around 450nm, together with phosphor materials.

The blue light excites the phosphor, which produces broader longer-wavelength emission.

The combination appears white:

Blue LED + Phosphor → Broad-Spectrum White Light

This is very different from a monochromatic red or blue LED, which has a relatively narrow spectral output.

Visible Spectrum and Color Temperature

The visible spectrum should not be confused with color temperature (CCT).

Wavelength describes spectral position and is usually measured in nm.

CCT describes the appearance of white light and is measured in Kelvin (K).

For example:

2700K → Warm White

3000K → Warm White

4000K → Neutral White

5000K → Daylight White

6500K → Cool Daylight

A 3000K white LED does not mean the LED emits a “3000K wavelength.” Its white appearance comes from a combination of wavelengths across part of the visible spectrum.

Visible Spectrum in Horticultural Lighting

The visible spectrum is particularly important in horticultural LED design.

Photosynthetically active radiation, or PAR, is conventionally defined as 400–700nm.

Important horticultural wavelengths include:

450nm — Blue

660nm — Deep Red

Many modern grow lights combine these wavelengths with broad-spectrum white LEDs.

Far-red around 730nm may also be added for specific plant responses, even though it lies outside the traditional PAR definition.

Visible Spectrum in LED Manufacturing

SMD LED manufacturers can produce components covering many spectral regions.

For example, LEDestar-type LED solutions may use packages such as 2835, 3030, 3535 and 5050 for different white-light and monochromatic applications.

The package size does not determine wavelength.

A 3535 LED, for example, might be designed as blue, red, deep-red, UV or infrared depending on its semiconductor structure and intended application.

For professional LED sourcing, important spectral specifications include peak wavelength, dominant wavelength, FWHM, radiant power, luminous flux, CCT and CRI, depending on whether the source is monochromatic or white.

Visible Light Spectrum Summary

The easiest way to remember the visible spectrum is:

Violet → Blue → Green → Yellow → Orange → Red

with wavelengths increasing approximately from:

380nm → 700nm

Below this region lies ultraviolet, while beyond the red end lies infrared.

For LED technology, this spectrum is fundamental because different wavelengths are selected for different applications—from 450nm blue for horticulture and white-LED pumping, to 660nm deep red for plant lighting, and wavelengths beyond the visible spectrum such as 850nm for infrared systems.

The visible spectrum therefore isn't simply a rainbow of colors. It is a specific region of electromagnetic radiation that forms the foundation for LED lighting, displays, horticulture, optical systems, and many other photonic technologies.