At What Distance Can the Human Eye Detect a Candle Flame?

TL;DR

This study uses CCD observations to determine the maximum distance at which the human eye can detect a candle flame, establishing it at approximately 2.6 km, contrary to some claims of 10 miles or more.

Contribution

It provides an empirical measurement of candle visibility distance using calibrated CCD data, clarifying misconceptions about human visual detection limits.

Findings

Candle flame detectable up to ~2.6 km by human eye.

A candle flame at 2.6 km has brightness similar to a 6th magnitude star.

Human eye cannot detect a candle flame at 10 miles or more.

Abstract

Using CCD observations of a candle flame situated at a distance of 338 m and calibrated with observations of Vega, we show that a candle flame situated at ~2.6 km (1.6 miles) is comparable in brightness to a 6th magnitude star with the spectral energy distribution of Vega. The human eye cannot detect a candle flame at 10 miles or further, as some statements on the web suggest.