Electromagnetic Spectrum Wavelengths: Complete Reference Guide

What Is the Electromagnetic Spectrum?

The electromagnetic spectrum is the complete range of electromagnetic radiation, organized by wavelength or frequency. All electromagnetic waves travel at the speed of light (299,792,458 m/s in vacuum) and consist of oscillating electric and magnetic fields.

The key relationship connecting wavelength and frequency is:

Since the speed of light is constant, wavelength and frequency are inversely proportional:

• Longer wavelength = Lower frequency = Lower energy
• Shorter wavelength = Higher frequency = Higher energy

The spectrum spans roughly 24 orders of magnitude in wavelength, from kilometers to femtometers.

Complete Electromagnetic Spectrum Overview

Here is the complete electromagnetic spectrum organized from longest to shortest wavelengths:

Radio Waves

Radio waves have the longest wavelengths in the electromagnetic spectrum, ranging from about 1 millimeter to over 100 kilometers.

Radio Wave Bands

Radio Wave Properties

• Propagation: Can travel around Earth's curvature (HF) or require line-of-sight (VHF/UHF)
• Penetration: Low frequencies penetrate water and soil; higher frequencies blocked by obstacles
• Energy: Extremely low photon energies, non-ionizing
• Detection: Antennas and electronic circuits

Common Applications

• AM radio: 535-1605 kHz (561-187 m wavelength)
• FM radio: 88-108 MHz (3.4-2.8 m)
• WiFi 2.4 GHz: 12.5 cm wavelength
• WiFi 5 GHz: 5.5 cm wavelength
• Cellular 4G: 700-2600 MHz (43-12 cm)
• 5G mmWave: 24-47 GHz (12-6 mm)

Microwaves

Microwaves occupy the region between radio waves and infrared, with wavelengths from about 1 millimeter to 1 meter.

Microwave Bands

Key Applications

• Microwave ovens: 2.45 GHz (12.2 cm) excites water molecules
• Weather radar: 2.8 GHz and 5.6 GHz
• Satellite communication: C-band, Ku-band, Ka-band
• Automotive radar: 77 GHz (3.9 mm) for collision avoidance
• Cosmic microwave background: Peak at 160 GHz (1.9 mm)

Infrared Radiation

Infrared (IR) radiation lies between microwaves and visible light, with wavelengths from about 700 nanometers to 1 millimeter.

Infrared Subdivisions

Thermal Radiation

All objects emit infrared radiation based on their temperature. Wien's law gives the peak wavelength:

Examples of thermal emission peaks:

• Human body (310 K): Peak at 9.35 μm (long-wave IR)
• Earth (288 K): Peak at 10.1 μm
• Sun (5778 K): Peak at 502 nm (visible green)
• Light bulb filament (2700 K): Peak at 1.07 μm (near-IR)

Applications

• Remote controls: 940 nm
• Fiber optic communication: 1310 nm and 1550 nm
• Night vision: 0.7-1 μm (active IR) or 8-14 μm (thermal)
• IR spectroscopy: Molecular fingerprinting 2.5-25 μm
• Heat lamps: 700 nm - 5 μm

Visible Light

Visible light is the narrow band of electromagnetic radiation that human eyes can detect, spanning wavelengths from about 380 nm (violet) to 700 nm (red).

Visible Light Colors

Key Wavelengths

• Peak human eye sensitivity: 555 nm (green-yellow)
• Red laser pointer: 650 nm
• Green laser pointer: 532 nm
• Blue laser pointer: 445 nm
• Sodium street lights: 589 nm (yellow)
• LED colors: Red 625 nm, Green 520 nm, Blue 465 nm

Why We See These Wavelengths

The sun's peak emission is in the visible range, so evolution optimized our eyes for these wavelengths. The atmosphere is relatively transparent to visible light (the "optical window"), allowing sunlight to reach Earth's surface.

Ultraviolet Radiation

Ultraviolet (UV) radiation has wavelengths shorter than visible light, from about 10 nm to 400 nm. UV carries enough energy to cause chemical reactions and biological effects.

UV Subdivisions

Biological Effects

• UV-A: Penetrates deep into skin, causes premature aging and wrinkles
• UV-B: Causes sunburn, triggers vitamin D production, primary cause of skin cancer
• UV-C: Most dangerous but blocked by atmosphere; used for sterilization at 254 nm

Applications

• Black lights: 365-400 nm (UV-A)
• Germicidal lamps: 254 nm (UV-C)
• Phototherapy: 311 nm (narrow-band UV-B) for psoriasis
• EUV lithography: 13.5 nm for advanced chip manufacturing
• UV curing: 365-405 nm for adhesives and coatings

The Ozone Layer

Ozone (O₃) in the stratosphere absorbs most UV-B and virtually all UV-C radiation. The ozone absorption peak is around 250 nm. This protective layer is essential for life on Earth.

X-rays

X-rays have wavelengths from about 10 picometers to 10 nanometers, with energies capable of penetrating soft tissue and ionizing atoms.

X-ray Classifications

X-ray Production

X-rays are produced when high-energy electrons strike a metal target. The resulting spectrum has two components:

• Bremsstrahlung (braking radiation): Continuous spectrum from electron deceleration
• Characteristic X-rays: Discrete lines from inner-shell electron transitions

Medical Applications

• Radiography: 40-120 kV (0.01-0.03 nm) for bone and chest imaging
• Mammography: 25-35 kV (soft X-rays for tissue contrast)
• CT scans: 80-140 kV
• Radiation therapy: 4-25 MV (mega-voltage, very hard X-rays)

Other Applications

• X-ray crystallography: Copper Kα at 0.154 nm determines molecular structures
• X-ray fluorescence: Element identification in materials
• Security screening: Baggage and cargo inspection
• X-ray astronomy: Observing black holes, neutron stars

Gamma Rays

Gamma rays have the shortest wavelengths (below ~10 pm) and highest energies in the electromagnetic spectrum. They originate from nuclear processes.

Gamma Ray Sources

Properties

• Highly penetrating: Can pass through meters of concrete or lead
• Ionizing: Energetic enough to strip electrons from atoms
• No charge: Not deflected by electric or magnetic fields
• Wavelength smaller than atoms: Cannot be focused by conventional optics

Applications

• Nuclear medicine: Tc-99m imaging at 140 keV
• PET scans: Detect 511 keV photons from positron annihilation
• Gamma knife surgery: Co-60 for brain tumor treatment
• Food irradiation: Cs-137 or Co-60 for sterilization
• Industrial radiography: Inspecting welds and materials

Gamma Ray Astronomy

The highest-energy photons in the universe come from extreme cosmic events:

• Gamma-ray bursts: Most energetic explosions, from collapsing stars
• Active galactic nuclei: Supermassive black holes
• Pulsars: Rotating neutron stars
• Cosmic ray interactions: High-energy particles striking atoms

Atmospheric Transparency

Earth's atmosphere blocks most of the electromagnetic spectrum, allowing only certain "windows" to pass through:

Atmospheric Windows

What Gets Blocked

• Gamma rays, X-rays, UV-C: Absorbed by upper atmosphere
• Most UV-B: Absorbed by ozone layer
• Most IR: Absorbed by water vapor and CO₂
• Low-frequency radio: Reflected by ionosphere

Electromagnetic Spectrum and Human Health

Ionizing vs Non-Ionizing Radiation

The boundary between ionizing and non-ionizing radiation occurs around 10 eV (124 nm), roughly in the extreme UV range:

• Non-ionizing (radio → visible → UV-A): Cannot break chemical bonds in DNA; thermal effects only at high intensity
• Ionizing (UV-C → X-rays → gamma): Can damage DNA and cause cancer; requires careful exposure limits

Safe Exposure Guidelines

• Radio/microwave: Limited by thermal effects (heating)
• Visible light: Eye damage from high intensity (lasers, sun)
• UV: Skin cancer risk increases with cumulative exposure
• X-rays: Measured in mSv (millisieverts); 1-10 mSv typical medical exposure
• Gamma rays: Occupational limit typically 20 mSv/year

Quick Reference Conversions

Convert between wavelength, frequency, and energy:

Use our wavelength calculator to quickly convert between any wavelength, frequency, and energy units across the electromagnetic spectrum.

Detailed EM Spectrum Applications by Band

Every region of the electromagnetic spectrum has unique properties that make it suited for specific applications. The following comprehensive table maps each spectral band to its most important real-world uses, the technology involved, and the physical principle exploited.

Visible Light Color Wavelengths with Hex Color Codes

The visible light portion of the spectrum spans only about 380-700 nm but contains the full rainbow of colors perceivable by the human eye. The following table provides specific wavelengths, corresponding colors, approximate hex color codes for digital representation, and associated photon energies.

Note that hex color codes are only approximations. True spectral (monochromatic) colors cannot be perfectly reproduced by RGB displays because they fall outside the sRGB color gamut. The human eye is most sensitive at 555 nm (yellow-green) under daylight conditions, which is why green lasers appear dramatically brighter than red or blue lasers of equal power.

EM Radiation Properties Comparison

Different regions of the electromagnetic spectrum have vastly different properties in terms of how they interact with matter, whether they can ionize atoms, and what sources produce them. This comparison table summarizes these key characteristics for each major band.

The boundary between ionizing and non-ionizing radiation occurs approximately at the UV-B/UV-C transition, around 10 eV photon energy (124 nm wavelength). Below this energy, photons cannot eject electrons from atoms or break chemical bonds. Above it, radiation becomes progressively more dangerous to biological tissue, which is why X-ray and gamma-ray exposure must be carefully controlled with shielding and dosimetry.

Penetration ability is inversely related to frequency for radio through IR (lower frequencies penetrate better), but this relationship reverses at higher energies: X-rays and gamma rays are more penetrating than UV precisely because their high-energy photons interact less frequently with matter through the dominant photoelectric effect at these energies.

Summary

Key points about the electromagnetic spectrum:

• All EM radiation travels at the speed of light in vacuum (299,792,458 m/s)
• Wavelength and frequency are inversely proportional: λ = c/f
• Energy increases with frequency: E = hf = hc/λ
• The spectrum spans ~24 orders of magnitude from radio waves to gamma rays
• Visible light (380-700 nm) is a tiny fraction of the full spectrum
• Ionizing radiation (UV-C, X-rays, gamma) can damage DNA; non-ionizing cannot
• Atmospheric windows allow only certain wavelengths to reach Earth's surface

Frequently Asked Questions