Morse code flashlight

1. 1

   Type a message, or tap a quick message: SOS, CQ, HELP, OK, HELLO or I LOVE YOU.

2. 2

   Set the speed. 5 to 7 WPM is easy to read by eye; the screen stays at 7 WPM or slower.

3. 3

   Turn on Repeat until stopped, a red flash for night vision or Beep with each flash if you want them.

4. 4

   Choose the light: Use the flashlight (Android in Chrome; allow the camera once), Flash the screen (any device, after a warning), or Preview here on the page’s lamp.

5. 5

   Point the light at whoever is reading. Tap Stop, press Esc or go back to end it.

6. 6

   To flash by hand instead, hold Hold to flash (or Space) for as long as the light should be on, or tap Tap on the full screen to make the whole screen the key.

• A real flashlight. On Android phones in Chrome, the page switches the camera’s flashlight on and off. It asks for the camera once, when you tap Use the flashlight, and keeps the flashlight ready for more messages.

• Safe screen flashing. The whole screen flashes white, red, green or blue and black at 7 WPM or slower, in full screen, after a warning. If your system asks for reduced motion, the screen and the lamp don’t flash.

• Each letter shown. The lamp on the page shows the letter being sent and its code, with a progress line. It mirrors the flashlight only at 7 WPM or slower.

• SOS as one signal. The SOS button sends ...---... with no gaps between the letters, the way the distress signal is sent.

• Beep with each flash. A tone in step with the light, to learn the code by eye and ear at once.

• Red for night vision. Red light keeps your eyes, and the reader’s, used to the dark.

• Flash by hand. Hold the key (or Space) and the light stays on while you hold it; or turn the whole screen into the key.

Light uses the same Morse timing as sound (ITU-R M.1677-1): the light is on for one unit for a dot and three for a dash, and off for one unit between the parts of a letter, three between letters and seven between words. Speed is counted with the word PARIS, so one unit lasts 1.2 ÷ WPM seconds: 240 ms at 5 WPM.

The screen is held to 7 WPM. At that speed the fastest flash, a dot and its gap, takes 343 ms: under three flashes a second, the limit WCAG 2.3.1 sets for flashing content (W3C).

The flashlight, which you point at someone, goes up to 15 WPM, though a phone can be slow to switch it, so slower reads more reliably. The lamp on the page mirrors it only at 7 WPM or slower.

How to read Morse code light

Watch for two lengths of light: a short flash is a dot, a flash about three times as long is a dash. The dark pauses come in three lengths:

• A short dark pause separates the parts of a letter.
• A longer one (three dots) ends the letter.
• A long one (seven dots) ends the word.

Write each letter’s dots and dashes down as it ends, then look them up in the Morse code alphabet. Ask the sender to go slowly (5 WPM or less) and to repeat.

To read flashes with your phone, point the Morse code light translator at them; to practice by eye, play Lighthouse keeper.

Blinking Morse code with your eyes

Blinking uses the same code: a quick blink is a dot, and a long blink, eyes held shut about three times as long, is a dash. Keep your eyes open for a pause between letters and a longer one between words. Go slowly and repeat, because the reader may not be able to ask.

The best-known case: in 1966, US Navy pilot Jeremiah Denton, a prisoner of war in North Vietnam, blinked T-O-R-T-U-R-E during a filmed propaganda interview (US National Archives).

To practice, set the speed to 3 WPM and preview the message: blink while the lamp is lit, open your eyes when it goes dark.

Common messages as light:

Worked out for SOS: nine flashes, three short, three long, three short, with one-unit gaps and no letter gaps. That is 3 + 3 × 3 + 3 = 15 units of light and 8 of dark, 23 units in all. At 5 WPM a unit is 240 ms, so one SOS takes 5.52 seconds.