Flash-to-bang: how far is the lightning?

Light arrives essentially now; thunder takes time. Counting the delay gives a rough distance. It is a field estimate, not a storm-tracking system.

Rule of thumb

A common teaching rule is about 3 seconds per kilometer or about 5 seconds per mile. Those assume a typical speed of sound and a straight path. Temperature, humidity and wind shift the true speed a little; terrain and reflections shift what you hear a lot.

Why apps still help

Manual counting works, but reaction time and forgotten counts get messy. A tap-to-tap timer, or automatic flash and boom detection with pair review, removes some of that friction while staying honest about uncertainty.

Lightning and Fireworks modes

DecibelDock's Distance tool supports Lightning and Fireworks framing. Tap mode needs no camera. Automatic mode pairs a brightness jump with a sound onset and lets you reject bad pairs.

What this is not

Flash-to-bang does not say whether a storm is approaching, where lightning will strike next, or whether you are safe. If thunder is close, follow local safety guidance from weather authorities — not an app estimate.

Temperature and speed of sound

Sound travels roughly 343 m/s near 20 C, a bit slower when cold and a bit faster when warm. Apps that let you set air temperature are adjusting that constant. The change is real but usually smaller than timing and path errors in a thunderstorm.

Multiple flashes

Storms produce overlapping events. Pairing the wrong boom with a flash invents a distance. Automatic modes should offer review; tap modes rely on your attention. When unsure, discard the pair.

Fireworks mode

The same timing idea applies to fireworks: see the burst, hear the boom, convert delay to distance. Crowds, echoes between buildings, and overlapping shells create the same pairing problems as thunder. Review candidates carefully and discard doubtful pairs.

Stay where local rules and common sense say is safe. An app distance is curiosity, not a seating chart for danger.

Putting it to work in DecibelDock

Open Flash-to-bang Distance after you read this guide so the ideas attach to real controls. Use the same phone, the same weighting or instrument preset, and the same physical position whenever you compare two scenes. Prefer a blank reading, a held value, or a written rejection over a number that looks definitive but came from silence, clipping or chaos.

DecibelDock is built for exploration and relative checks on Android. It is not a calibrated or certified sound level meter, not a medical device, and not a substitute for professional instruments when safety, health or compliance are on the line. Direction, Doppler and Distance stay approximate and depend on your phone. The learn section exists to make those limits understandable — and to help the feature pages show up for the questions people already type into a search box.

When you are done experimenting, skim a related article below and the matching feature page. Internal links are intentional: each guide should send you somewhere useful next, not leave you on a dead-end paragraph.

If something in the app disagrees with this guide after a future update, trust the in-app How to use notes for that build, and treat marketing copy as secondary to what the screen actually shows.

Key takeaways

• Use the same phone and setup when you compare scenes.
• Prefer a blank or rejected result over a confident wrong number.
• Phone tools are for exploration and relative checks, not certification.
• Read the matching feature page for what the app actually shows on screen.