How to signal Morse code with a flashlight
To signal Morse code with a flashlight, let the light show for one unit of time for a dit and three units for a dah, and keep it dark for one unit between the parts of a letter, three units between letters and seven between words. Pick a unit long enough to see clearly, about half a second while you learn, and keep it steady. The light carries the same rhythm a radio tone does, only slower.
That is the whole method. The rest is about doing it cleanly enough that someone across a field, a parking lot or a dark yard can read what you meant. One rule comes before all of it: if anyone needs help, call your local emergency number first, wherever you can. A light can add to a call; it never replaces one.
Choose a unit you can keep
Morse timing is built on one unit, and every part of the signal is a whole number of them. With sound, a unit at 20 words per minute is 60 milliseconds. With light, that is far too fast: the eye needs longer to tell a short flash from a long one, and your hand needs longer to make them. Start slow.
| Unit | Dit (light on) | Dah (light on) | Gap between letters | Gap between words | Speed |
|---|---|---|---|---|---|
| 0.25 s | 0.25 s | 0.75 s | 0.75 s | 1.75 s | about 5 WPM |
| 0.5 s | 0.5 s | 1.5 s | 1.5 s | 3.5 s | about 2.4 WPM |
| 1 s | 1 s | 3 s | 3 s | 7 s | about 1.2 WPM |
The gap inside a letter, between one flash and the next, is always one unit. The speeds come from the standard rule that a dit lasts 1200 divided by the words per minute, in milliseconds. That is slow by radio standards and fine for light: a clean slow signal beats a quick one nobody can read.
Count to keep the unit even. Say “one” to yourself for a dit, “one, two, three” for a dah, and count the dark gaps the same way. If counting in your head drifts, tap your foot, or let a metronome tick the unit for you while you practice. Morse code timing: the 1, 3, 7 rule explains why the gaps matter as much as the flashes.
Switching or covering the light
There are two ways to make a flash: switch the light on and off, or leave it on and block it.
Covering is usually cleaner. Turn the flashlight on, then cover and uncover the lens with your palm, a book or a piece of card. Your hand can move faster and more evenly than many switches, and the light stays at full brightness the whole time. A card held in front of the lens and swung aside works like a shutter.
Switching works if the switch suits it. Some flashlights have a momentary mode, where the light stays on only while you hold the button; that behaves like a Morse key. Many do not. A click switch you must press fully and release for each flash can be slow and tiring, and on some LED flashlights quick clicks step through brightness levels or into a strobe, which garbles the message. An old filament bulb may also take a moment to brighten and fade, which can soften short flashes. If your light misbehaves, cover it instead.
A phone flashlight is usually awkward to switch from the screen at Morse pace. Turn it on once, then cover and uncover it with a finger.
Whichever way you choose, hold the light still. Brace your elbow on a wall, a car roof or your knee. A beam that wobbles between flashes can sweep off the person watching, and to them a moving light reads as a gap.
Send a message, step by step
- Write it out first. Put the message on paper in dots and dashes, one letter per group, with a slash between words. Short messages work best: HI, OK, a name, a meeting time. Reading from the paper keeps your mind on timing instead of on remembering the code.
- Agree on a start. Before you begin, decide how the watcher will know a message is coming. A few seconds of steady light, then dark, is an obvious choice.
- Send at your chosen unit. OK is O
---then K-.-: three long flashes, a three-unit gap, then long, short, long. - End clearly. Send AR,
.-.-., for “end of message”, or K,-.-, for “over, your turn”, if you have agreed on those. - Repeat it. Light is easy to miss. Send the whole message twice, with a long dark pause between.
If you make a mistake, send the error signal, eight dits ........, then send the word again. It is better than trying to patch a single letter.
Reading a light from a distance
Receiving light is harder than sending it, so give the watcher every chance.
- Watch the dark as well as the light. A dah is three times a dit, and a word gap is a little more than twice a letter gap. Many misreadings come from the gaps, not the flashes.
- Write as you watch. Mark a dot or a dash on paper for each flash and a space for each letter gap, without trying to decode. Decode afterwards, when the light has stopped. Two people help: one calls out “short” and “long”, the other writes.
- Shade your eyes from other lights. Street lamps, car headlights and a bright screen near you all make a distant light harder to follow.
- Mind the afterimage. In the dark, a bright light can leave a glow in your eyes that makes a short gap harder to see. Slow the unit down for night signals.
Answer with the same light. R, .-., means “received”. If you could not read it, send RPT, .-. .--. -, for “repeat”, or agree beforehand on a simpler “say again” signal.
Never point a light at anyone’s eyes, and never at vehicles or aircraft. Up close, practice by pointing the light at a wall, a ceiling or the ground between you, or turn it to its lowest setting. Over a distance, aim toward where the watcher stands, never into their face, and use no more brightness than they need.
Practice SOS the right way
SOS is not three letters. It is a prosign: one character of nine elements, sent as ...---... with only the one-unit gaps that belong inside a character. With a flashlight that means three short flashes, three long, three short, each separated by one unit of dark, with no longer pause between them. Sent with letter gaps, as ... --- ..., it is the letters S, O and S.
At half a second a unit, the nine flashes and their gaps take 23 units, about 11.5 seconds. Add the seven-unit word gap and the signal comes round every 15 seconds or so. Practice it slowly, indoors or against a wall, where nobody could take it for a real distress signal. SOS in Morse code: how to send it correctly goes through the rhythm in detail.
Know SOS, but never use a flashlight instead of calling for help. If someone needs help, call your local emergency number first, wherever you can; a light can add to that call, never replace it.
Getting the rhythm into your hands first
Flashing is easier once each letter is a rhythm you know, not a pattern you look up. Dot & Dash has no light of its own; it is a Morse machine you press on a Mac, with a tone and a paper tape on screen. Keying letters on it in its course, then flashing them, means your hand already knows that K is long, short, long. Its Text to Morse turns any message into dots and dashes you can copy onto a card and read from while you signal.
Light signaling has a long history at sea, where signal lamps still flash Morse between ships; flashing Morse at sea covers that side. If you have no flashlight at all, tapping and blinking shows how to send Morse with nothing but your hands and eyes.
Questions
How long should a flash be for a dit?
About half a second is a good start for light. Keep every dit the same length, make each dah three times as long, and grow the dark gaps in the same proportion: one unit inside a letter, three between letters, seven between words.
Is it better to switch the flashlight or cover it?
Covering is usually cleaner, because your hand can move faster than many switches and the light stays at full brightness. Switching works best with a light that has a momentary mode.
How do I flash SOS?
Three short flashes, three long and three short, all separated by one unit of dark and with no longer pauses between them, because SOS is sent as one continuous character. Leave a long dark pause before you repeat it.
Can I read Morse from a light at night?
Yes, and lights are easiest to see in the dark, but a bright light can leave an afterimage that makes short gaps harder to see. Slow the signal down and write down short and long flashes as they come, then decode afterwards.