Morse Code Light Signal
Your screen becomes the lamp. Type a message and let it blink.
Light is the oldest way to send Morse code and the one that still works when nothing else does. It needs no radio, no network and no shared language - only a lamp that can be switched and someone at the other end who knows the rhythm. A phone screen at full brightness carries surprisingly far in the dark.
Why the speed is limited here
This is the one tool on the site that can genuinely harm someone, so it is worth being plain about it.
Flashing light between roughly 3 and 55 times per second can trigger seizures in people with photosensitive epilepsy. Morse code at ordinary speeds lands squarely in that range: a run of dots at 20 words per minute flashes over eight times a second. The accessibility guidelines draw the line at three flashes per second, which corresponds to about 7 words per minute.
So this page starts at 7, shows the flash rate as you change it, and marks it when you go past the limit. Full screen only happens when you ask for it, and if your system is set to reduced motion the flashing does not run at all. None of that stops you sending faster if you need to - it just means you are told.
Sending light in the field
- Slow beats fast. Someone reading light without practice needs long marks and long gaps. Five words per minute is not too slow when the alternative is not being understood.
- Aim, then send. Point the lamp at the target before starting. A signal swept across the horizon reads as a flicker, not a message.
- Repeat with a pause. One transmission is easy to dismiss as a reflection. The same pattern three times with a gap between reads as deliberate.
- Keep it short. SOS, a name, a direction. Anything longer will not be copied correctly by an untrained receiver.
A dedicated torch beats a phone: it is brighter, more directional, and it does not run your battery down when you may need it for other things.
Where light signaling is still used
Navies still train signaling by lamp, because it cannot be intercepted at a distance or jammed, and it works under radio silence. Aldis lamps are still carried on warships for exactly that reason.
Beyond that it turns up wherever radio is not an option: between climbers, from a stranded vehicle to a search aircraft, across a valley, or through a window. It also works through glass, which sound does not.
Frequently asked questions
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How do I send Morse code with a light?
Short flash for a dot, a flash about three times as long for a dash. Pause briefly between letters and clearly longer between words. This page does the timing for you; outdoors, count the beats yourself.
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Is flashing light dangerous?
It can be. Flashing above three times per second can trigger seizures in people with photosensitive epilepsy. At speeds above about 7 words per minute this page crosses that threshold, which is why the rate is shown and marked.
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How far does a phone screen carry?
In full darkness, a few hundred meters with a clear line of sight. A torch reaches considerably further and is easier to aim, which matters more than raw brightness.
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Why is the light not white?
A softer tone is easier on the eyes for a signal that repeats, and it makes no difference to readability - the rhythm carries the message, not the brightness.