How to Use Light to Send Morse Code Signals: A Practical Field Guide
Flashing a light to send Morse code is one of the oldest visual signaling methods—and it still works. Whether you're signaling across a valley, communicating during a power outage, or just want a backup to electronic communication, light-based Morse is a skill worth learning properly. Here's what actually works, what doesn't, and how to do it right.
Why Light Signals Still Matter
Radio requires equipment. Voice requires proximity. But light? A functioning flashlight, the sun reflected off a mirror, or even a campfire can transmit Morse code for miles under the right conditions.
During the 2021 Caldor Fire evacuation in California, ham radio operator Mike Paulson (KM6YPF) used a tactical flashlight to signal his location to search teams when his radio battery died. "I had maybe 30 seconds of charge left on the radio, but my flashlight had hours. I flashed SOS and my grid square in Morse. They found me within 40 minutes."
This isn't a common scenario. But when you need it, nothing else substitutes.
The Physics of Light Signaling: What Determines Your Range
Before diving into technique, understand the variables:
Distance Factors
| Factor | Effect | Practical Implication |
|---|---|---|
| Light intensity | Lumens determine base visibility | A 1000-lumen flashlight beats a 100-lumen one |
| Beam focus | Narrow beams travel farther | Zoom/focus flashlights extend range |
| Atmospheric conditions | Haze, rain, fog reduce range dramatically | Clear nights can achieve 10-20x the range of foggy conditions |
| Background contrast | Dark background helps | Night signals are visible at 10-50x daytime distance |
| Observer preparation | Dark-adapted eyes see more | Waiting 20-30 minutes in darkness improves reception |
Realistic Range Expectations
Direct light source (flashlight):
- Urban environment, daytime: 100-300 meters
- Rural, clear night: 2-10 kilometers (depending on lumens)
- At sea, clear night: Up to 15 kilometers with powerful light
Heliograph (mirror flash):
- Clear day: 50-150 kilometers (with proper technique)
- U.S. Army Signal Corps records from the 1890s document heliograph communications over 200 kilometers in Arizona
The heliograph's range advantage comes from reflecting concentrated sunlight rather than generating light—the sun provides approximately 100,000 lumens per square meter on a clear day.
Equipment: What You Need and What Actually Works
Flashlights for Morse Signaling
Not all flashlights are equal for Morse code. The critical feature isn't maximum brightness—it's switching response time.
Essential characteristics:
Tested recommendations by price range:
| Budget | Model Type | Notes |
|---|---|---|
| Under $30 | Basic tactical with tail switch | Look for "instant on" in specs |
| $30-80 | Quality EDC with programmable UI | Convoy, Wurkkos, Sofirn brands offer good value |
| $80+ | Dedicated signaling lights | Fenix TK series, Streamlight have fast switches |
Avoid for Morse signaling:
- Headlamps (poor aiming, usually slow switches)
- Lanterns (diffuse light, no directionality)
- Phone flashlights (slow response, poor intensity, drains battery)
Jim Crawford, a former Coast Guard signalman, puts it simply: "I've trained dozens of people in visual signaling. The number one equipment mistake is using whatever flashlight they have instead of one that actually switches fast. A $20 tactical light from Amazon outperforms a $150 multi-mode flashlight if the cheap one has a proper tail switch."
Heliograph and Mirror Signaling
For daytime signaling, reflected sunlight travels much farther than any flashlight.
Commercial signaling mirrors:
- Usually have a sighting hole or grid
- Provide 2x2 inch to 4x4 inch reflective surface
- Cost $10-30 for quality models
Improvised options:
- CD/DVD (surprisingly effective, compact)
- Any polished metal surface
- Rearview mirror from a vehicle
- Phone screen (low efficiency but works)
Aiming technique (critical):
This "double V" sighting method was standard military procedure because it works without specialized equipment.
Proper Timing: The Part Most People Get Wrong
Light Morse code follows the same timing rules as sound, but people consistently make the same errors:
International Standard Timing
| Element | Duration |
|---|---|
| Dit (dot) | 1 unit |
| Dah (dash) | 3 units |
| Gap between dit/dah in same letter | 1 unit |
| Gap between letters | 3 units |
| Gap between words | 7 units |
The common mistake: People make dits and dahs the right length but rush the gaps. A letter gap that's too short turns "A B" (.- / -...) into something unreadable.
Choosing Your Speed
Speed is measured in words per minute (WPM), based on the word "PARIS" (50 units total).
| WPM | Dit duration | Good for |
|---|---|---|
| 5 WPM | 240ms | Beginners, long distance, poor conditions |
| 10 WPM | 120ms | Comfortable conversation pace |
| 15 WPM | 80ms | Experienced operators |
| 20+ WPM | 60ms or less | Impractical for visual signaling |
Practical recommendation: Start at 5 WPM for light signaling. Even experienced CW operators should slow down for visual work—your hand and eye coordination differs from keying.
"I can copy 30 WPM on radio," says Sarah Kim, an amateur operator in Oregon. "But visual? I max out around 12, and that's after years of practice. There's something about the light that's harder to parse at speed."
Character Priority: What to Learn First for Light Signaling
If you're learning Morse specifically for light signaling, prioritize these characters:
Emergency Characters (Learn First)
| Character | Code | Why Priority |
|---|---|---|
| S | ... | Part of SOS |
| O | --- | Part of SOS |
| E | . | Most common letter, easiest |
| T | - | Second most common, easiest |
| A | .- | Common, simple |
| N | -. | Common, simple |
SOS sequence: ... --- ... (no letter gaps—it's a single prosign)
Numbers for Coordinates
If signaling location, you'll need numbers:
| Number | Code |
|---|---|
| 0 | ----- |
| 1 | .---- |
| 2 | ..--- |
| 3 | ...-- |
| 4 | ....- |
| 5 | ..... |
| 6 | -.... |
| 7 | --... |
| 8 | ---.. |
| 9 | ----. |
Notice the pattern: numbers go from five dahs (0) to increasing dits replacing dahs (1-5), then reverse (6-9). This makes them easier to remember.
Practical Exercises for Building Skill
Exercise 1: The Kitchen Table Drill
Practice with a partner across a room before going outside.
Target: 90% accuracy at 5 WPM before moving outdoors.
Exercise 2: The Parking Lot Distance Test
Once comfortable indoors:
Document your results. Knowing "my flashlight works reliably to 200 meters" is more useful than guessing.
Exercise 3: Mirror Aiming Practice
For heliograph work:
Real-World Protocols: How Visual Morse Actually Gets Used
Calling and Answering
Standard visual calling sequence:
Error Correction
If you make an error while sending:
End of Message
Send AR (.-.-.) to indicate message complete. If expecting reply, send K (-.-) If no reply expected, send SK (...-.-) meaning "end of contact"
Emergency Signaling: SOS and Beyond
The SOS Prosign
SOS is sent as a single unit: ... --- ... with no gaps.
Why SOS? Contrary to popular belief, it doesn't stand for "Save Our Souls." It was chosen in 1906 because it's distinctive—the only prosign with this pattern—and easy to recognize even in degraded conditions.
Signaling Aircraft
If signaling to search aircraft:
When NOT to Use Light Signals
Light signals can work against you:
- In hostile situations: You're also signaling your position to everyone
- During lightning storms: You won't be seen and risk exposure
- In dense fog: Light scatters; sound travels better
Maintaining Skills: Practice Schedule
Visual Morse is perishable. A realistic maintenance schedule:
| Your Goal | Practice Frequency | Session Length |
|---|---|---|
| Emergency backup only | Monthly | 15 minutes |
| Casual proficiency | Weekly | 20-30 minutes |
| Reliable field skill | 2-3x weekly | 30 minutes |
For conversion practice and character lookup during training, any Morse code reference can help verify your accuracy. The key is consistent, deliberate practice—not cramming before a camping trip.
Advanced Technique: Combining Light and Other Signals
Experienced field operators often combine methods:
Light + Audio
In noisy environments, simultaneous light and whistle/horn signals reinforce each other. The timing stays identical; the light confirms what the ear might have missed.
Light + Radio
During emergency exercises, operators sometimes relay visual signals via radio for recipients beyond visual range:
"Station 2, I'm receiving visual from Station 1. They're sending: W-A-T-E-R space N-E-E-D-E-D..."
This radio relay of visual Morse extended practical range during the 2017 hurricane responses in the Caribbean.
Common Questions
"Can I use my phone flashlight?"
In an emergency, yes. For practice or reliability, no. Response time is too slow, and you'll drain your phone battery."How do I practice alone?"
Record yourself and play back. Watch for rushed letter gaps—they're the biggest source of errors."What's the longest practical distance?"
A Coast Guard signalman named Rodriguez documented clear visual Morse at 28 miles (45 km) using a heliograph between San Diego and Catalina Island in optimal conditions. For flashlights, 5-10 miles is a realistic maximum with high-powered lights on clear nights."Should I learn the visual alphabet chart first?"
No. Learn the sounds (or in this case, the rhythm). Visual charts create translation overhead—you'll be slow forever. Learn dits and dahs as a rhythm pattern, then apply that to light.The Practical Bottom Line
Light-based Morse code is genuinely useful in specific situations:
- Power outages
- Equipment failure
- Long-distance silent communication
- Emergency signaling
It's not a replacement for radio or phones. It's a backup, and a reliable one if you've practiced.
The skill itself isn't difficult—it's simple physics and memorization. The hard part is maintaining it. Monthly practice, proper equipment, and realistic expectations about range and conditions separate people who can actually use this skill from those who just read about it.
Field notes compiled from: U.S. Army Field Manual 21-60 (Visual Signals), Coast Guard Auxiliary signaling training materials, interviews with amateur radio operators experienced in field communications, and personal testing with various equipment configurations.