Light Waves – vs – Radio Waves

Same Physics. Vastly Different Journeys.

When we switch on a Wi-Fi router, talk on a walkie-talkie, tune into a ham radio net, or stream a 4K movie over fiber, we are using electromagnetic waves. Some of these waves are called radio waves, others light.

They come from the same family.
They obey the same equations.
Yet their behavior, reach, speed, and use cases feel radically different.

So what really separates light from radio waves?

Let’s go deeper than wavelength charts and explore how they propagate, how they carry information, and why sometimes they are interchangeable and sometimes absolutely not.

1. Same Family: The Electromagnetic Spectrum

At a fundamental level: Light and radio waves are the same thing. They are both electromagnetic (EM) radiation.

They differ only in frequency and wavelength.

Property	Radio Waves	Light (Visible / Optical)
Frequency	kHz → GHz	Hundreds of THz
Wavelength	Kilometers → millimeters	~400–700 nm
Energy per photon	Very low	Much higher

But frequency alone does not explain their real-world behavior.
The real differences emerge when these waves move through space and matter.

2. Propagation: How They Travel Through the World

Radio Waves are The Masters of Reach

Radio waves are extremely forgiving.

They can:

• Diffract around obstacles
• Penetrate walls, foliage, and terrain
• Reflect off the ionosphere
• Bend slightly due to atmospheric conditions

This gives rise to:

• Ground-wave propagation
• Sky-wave (ionospheric) propagation
• Tropospheric ducting
• Non-line-of-sight (NLOS) communication

Radio doesn’t demand visibility, it demands physics cooperation.

Light Waves are Strict, Elegant, and Demanding

Light behaves very differently.

It:

• Travels almost strictly line-of-sight
• Does not diffract significantly around obstacles
• Is easily blocked by walls, fog, smoke, dust
• Reflects and refracts in predictable ways

This means:

• No sky-wave or bending around terrain
• Precision alignment is critical
• Propagation paths must be engineered

That’s why optical fiber, laser links, and free-space optics require tight control and accuracy.

Light demands discipline.

3. Carrying Information: Modulation Is the Great Equalizer

Here’s a beautiful truth:

Light and radio carry information in exactly the same way.

Both use:

• Amplitude modulation
• Frequency modulation
• Phase modulation
• Quadrature modulation
• Advanced digital schemes

Whether it’s:

• CW on HF
• QPSK over satellite
• Ethernet over fiber
• Laser links between buildings

The math is the same only The medium is different.

4. Data Rates: Why Light Wins on Speed

The capacity of a communication channel depends largely on:

• Available bandwidth
• Signal-to-noise ratio

Light’s Superpower is Enormous Bandwidth

Visible and infrared light operate at terahertz frequencies.

That means:

• Massive bandwidth availability
• Extremely high symbol rates
• Dense wavelength multiplexing

Modern fiber links routinely carry terabits per second.

Radio’s Constraint is Crowded Spectrum

Radio waves:

• Operate in limited, regulated bands
• Face interference from countless sources
• Must obey power and emission limits

Even with:

• MIMO
• Beamforming
• Millimeter wave
• Carrier aggregation

Wireless struggles to match fiber’s raw capacity.

Radio trades speed for freedom.

5. Interaction With the Environment

Aspect	Radio Waves	Light Waves
Walls & Buildings	Often penetrate	Mostly blocked
Weather	Usually minor effect	Fog, rain, dust are critical
Directionality	Can be omnidirectional	Highly directional
Interference	High (shared spectrum)	Very low (controlled paths)

This explains:

• Why Wi-Fi drops indoors
• Why lasers fail in fog
• Why HF thrives at night
• Why fiber is immune to EMI

6. Energy & Safety

Despite sounding powerful:

• Radio waves are extremely low energy per photon
• Visible light photons are far more energetic

Yet:

• Both are non-ionizing
• Both are safe within regulated limits

Ironically:

• A focused laser can burn
• A kilowatt HF transmitter usually won’t as much

Power density matters more than frequency.

7. Where Light and Radio Are Used for the Same Purpose

Identical Use Cases, Different Mediums – This is where things get fascinating.

Use Case	Radio Implementation	Light Implementation
Internet backbone	Microwave links	Optical fiber
Point-to-point links	RF microwave	Free-space laser
Satellite comms	RF transponders	Optical satcom
Data centers	Copper/RF	Fiber optics
Secure links	Spread spectrum RF	Narrow-beam lasers

In all these cases:

• Protocols are similar
• Error correction is similar
• Modulation is similar

Only physics and constraints change.

8. Why We Need Both

If light were perfect:

• We wouldn’t need Wi-Fi, LTE, or ham radio

If radio were perfect:

• We wouldn’t need fiber optics

Reality demands:

• Radio for mobility, reach, resilience
• Light for speed, capacity, precision

They are not competitors but they are partners.

9. A Ham’s Perspective

For radio amateurs and communication engineers:

• Understanding light explains why higher frequencies behave differently
• Optical comms feel like VHF/UHF on steroids
• Terahertz bridges the gap between RF and optics
• The future blends radio intelligence with optical speed

The electromagnetic spectrum is a continuum, not silos.

Final Thought

Light and radio waves are siblings separated not by nature, but by scale, discipline, and opportunity.

One conquers distance.
The other conquers data.
Together, they carry the modern world.

73, DE VU2JDC