Light Spectrum Wavelengths

Light is a form of electromagnetic radiation that travels in waves. The electromagnetic spectrum covers an enormous range of wavelengths, from extremely short gamma rays to radio waves that can be kilometers long.

The portion humans can see is called visible light, which generally covers wavelengths of approximately 380 to 700 nanometers (nm). However, many important lighting technologies—including UV LEDs, horticultural LEDs, and infrared LEDs—operate outside this visible range.

What Is Wavelength?

Wavelength is the distance between two corresponding points of consecutive electromagnetic waves, such as two peaks.

It is represented by the Greek letter:

λ (lambda)

For light and LED applications, wavelength is commonly measured in:

• nm — nanometers

• µm — micrometers

• mm — millimeters

• m — meters

One nanometer equals:

1 nm = 0.000000001 meter = 10⁻⁹ m

Visible and LED wavelengths are therefore extremely small.

Electromagnetic Spectrum Wavelengths

The electromagnetic spectrum can be divided approximately as follows:

The boundaries between these categories are conventions rather than perfectly sharp physical divisions, so ranges can differ slightly among references.

Visible Light Spectrum Wavelengths

Visible light is the part of the electromagnetic spectrum detected by the human eye.

A useful approximate range is:

380 nm → 700 nm

Different wavelengths produce different color sensations.

There are no perfectly sharp boundaries between these colors. Human color perception changes gradually across the spectrum.

Violet Light: 380–450 nm

Violet occupies the shortest-wavelength region of visible light.

Common LED wavelengths include:

• 405 nm

• 410 nm

• 420 nm

• 430 nm

Violet LEDs can be used in specialty lighting, fluorescence excitation, curing-related applications, horticulture, and scientific equipment.

At the lower end of this range, violet light approaches ultraviolet radiation.

Blue Light: 450–495 nm

Blue is one of the most important wavelength regions in LED technology.

Common LED wavelengths include:

450 nm, 455 nm, 460 nm and 470 nm

Blue LEDs are used in:

• White LED production

• Displays

• Horticultural lighting

• Aquarium lighting

• Stage lighting

• Phototherapy equipment

Most phosphor-converted white LEDs begin with a blue LED die, often with emission somewhere around the mid-450 nm region.

The blue photons excite phosphor materials that emit longer wavelengths. The combination appears white to the human eye.

Green Light: 495–570 nm

Green light lies approximately between blue and yellow.

Typical green LEDs may operate around:

• 515 nm

• 520 nm

• 525 nm

• 530 nm

• 535 nm

The human photopic visual system is particularly sensitive around the green-yellow region, with peak photopic sensitivity near 555 nm.

Green LEDs are widely used in indicators, displays, RGB lighting, signage, horticulture, and specialty illumination.

Yellow Light: 570–590 nm

Yellow wavelengths fall approximately between:

570–590 nm

Yellow LEDs are commonly used for:

• Indicators

• Warning lights

• Signage

• Decorative lighting

• Specialty spectral applications

The exact perceived color depends on the LED's peak wavelength and spectral width.

Amber Light: Around 590 nm

Amber is often treated separately in the LED industry because it is commercially important.

Common monochromatic amber LEDs operate around:

585–595 nm

with approximately 590 nm being a widely used target.

Applications include:

• Automotive turn signals

• Warning lights

• Street and outdoor lighting

• Decorative lighting

• Low-blue-light applications

A monochromatic 590 nm amber LED should not be confused with a phosphor-converted warm-white LED with a very low CCT.

Orange Light: 590–620 nm

Orange sits between yellow/amber and red.

Common LED wavelengths include:

• 600 nm

• 605 nm

• 610 nm

• 615 nm

Orange LEDs are commonly found in signaling, automotive, decorative, and architectural applications.

Red Light: 620–700 nm

Red covers the longest wavelengths normally classified as visible light.

Common red LED wavelengths include:

620 nm, 625 nm and 630 nm

Deeper red LEDs commonly operate around:

650–660 nm

Red LEDs are widely used for:

• Indicators

• Displays

• Automotive lighting

• Horticultural lighting

• Stage lighting

• Photobiomodulation devices

Deep Red: 660 nm

660 nm is especially important in horticultural lighting.

It lies in the deep-red portion of the spectrum and corresponds well with important photosynthetic absorption regions.

As a result, 660 nm LEDs are frequently combined with blue and white LEDs in professional grow lights.

A common horticultural spectral design might include:

450 nm Blue + White + 660 nm Deep Red

The exact combination depends on crop, growth stage, fixture architecture, and production goals.

Far-Red: 700–750 nm

Far-red lies just beyond the conventional 400–700 nm PAR definition, although plants can respond strongly to it.

One of the most commonly used LED wavelengths is:

730 nm

Far-red can influence plant photomorphogenesis through the phytochrome system, affecting responses such as stem elongation, canopy architecture, and flowering in some species.

Modern horticultural fixtures may therefore combine:

Blue + White + Deep Red + Far-Red

Ultraviolet Light

Ultraviolet wavelengths are shorter than visible violet light.

UV is commonly divided into:

Common UV LED wavelengths include:

365 nm, 385 nm, 395 nm and 405 nm

Note that 405 nm is generally classified as visible violet rather than UV under the conventional 400 nm boundary, although commercial terminology can sometimes blur this distinction.

UV LEDs have applications in curing, fluorescence, inspection, printing, sensing, disinfection, and specialized horticultural systems.

Infrared Light

Infrared begins beyond the red end of the visible spectrum.

A broad definition is:

~700 nm to 1 mm

Infrared can be divided into several regions depending on the scientific or industrial classification being used.

Common LED wavelengths include:

• 730 nm

• 810 nm

• 830 nm

• 850 nm

• 940 nm

850 nm and 940 nm are particularly common in IR LED products.

Applications include:

• Security cameras

• Night vision

• Remote controls

• Sensors

• Machine vision

• Biometric equipment

• Photobiomodulation equipment

Because infrared is outside the visible spectrum, an IR LED can produce substantial radiant power without appearing bright to the human eye.

Wavelength vs. Frequency

Wavelength and frequency are inversely related.

The relationship is:

c = λf

where:

c = speed of light
λ = wavelength
f = frequency

Therefore:

Shorter wavelength → Higher frequency

Longer wavelength → Lower frequency

For example, blue light has a higher frequency than red light.

Wavelength vs. Photon Energy

Photon energy is also related to wavelength:

E = hc / λ

This means:

Short wavelength → Higher photon energy

Long wavelength → Lower photon energy

Therefore, a violet photon carries more energy than a red photon.

This becomes particularly important when comparing UV, visible, and infrared radiation.

LED Wavelengths

LEDs are especially useful because semiconductor technology can produce relatively narrow spectral bands.

Some commonly specified LED wavelengths are:

Peak Wavelength and Dominant Wavelength

When selecting LEDs, it is important to understand that LEDs do not normally emit only one exact wavelength.

For example, a product described as a 660 nm LED has a spectral distribution centered around a particular region.

Two common specifications are:

Peak wavelength (λp) — wavelength where the spectral output reaches its maximum.

Dominant wavelength (λd) — a colorimetric measurement describing the perceived color of visible light.

These values are not necessarily identical.

Spectral Bandwidth and FWHM

Another important specification is FWHM — Full Width at Half Maximum.

FWHM describes the width of an LED's spectral output measured at half its maximum intensity.

For example, two LEDs may both be described as 660 nm products but have different spectral bandwidths.

This can matter considerably in horticulture, medical devices, machine vision, sensing, and other wavelength-sensitive applications.

White LEDs Are Different

A white LED is usually not described by one visible wavelength because it emits across a relatively broad spectrum.

Instead, white LEDs are commonly specified using:

• CCT (Correlated Color Temperature)

• CRI (Color Rendering Index)

• Chromaticity coordinates

• Spectral Power Distribution (SPD)

Typical CCT values include:

2700K — Warm White

3000K — Warm White

4000K — Neutral White

5000K — Daylight

6500K — Cool White

Therefore, comparing a 660 nm red LED with a 4000K white LED requires different optical parameters.

Why Wavelength Matters in LED Selection

Selecting the correct wavelength can be critical for professional LED applications.

For horticulture, blue, deep-red, and far-red wavelengths can influence photosynthesis and plant development.

For photobiomodulation, red and near-infrared wavelengths such as 630, 660, 810, 830, and 850 nm are commonly investigated and used.

For machine vision, wavelength selection can improve contrast between objects and backgrounds.

For security cameras, 850 and 940 nm infrared LEDs are common.

For automotive lighting, wavelength and color specifications help ensure appropriate signaling performance.

For general illumination, however, CCT, CRI, luminous efficacy, and SPD are usually more useful than specifying a single wavelength.

The light spectrum covers an enormous range of wavelengths, while human vision occupies only a small region of approximately 380–700 nm.

Within the visible spectrum, shorter wavelengths appear violet and blue, while longer wavelengths appear orange and red. Beyond visible light are important regions such as UV and infrared.

For LED applications, commonly used wavelengths include 365/395 nm UV, 450 nm blue, 525 nm green, 590 nm amber, 630 nm red, 660 nm deep red, 730 nm far-red, and 810–940 nm near-infrared/infrared.

Understanding wavelength is particularly important when selecting LEDs for horticulture, outdoor lighting, photobiomodulation, machine vision, automotive lighting, displays, sensing, and other specialized applications. For professional LED selection, wavelength should be considered together with radiant power, spectral bandwidth, efficiency, drive current, thermal performance, and reliability.