How far can the human eye see a single lit candle?

Question

You light a candle how far away can people see it

Answer 1

Under ideal conditions, about three and a half miles.

For a point source against a dark background, and with a fully dark-adapted human eye, the threshold for human visibility T (in footcandles) can be found by this equation:

ln T = .0828 [K ln(B)]^2 + .194[K ln(b)] - 9.73

... where B is the background brightness in nanoLamberts, and K = .4343. A perfectly dark, clear night sky will have a brightness of about 100 nanoLamberts, and this equation is valid only for backgrounds of 0.1 nanoLamberts or greater, which is essentially totally dark.

Solving this equation for T, the threshold visibility against a background of 0.1 nL gives us 5.3 x 10^-5 footcandles, which is the brightness of 1 candle at 18,792 feet, or 3.6 miles.

Allowing for atmospheric attenuation will reduce that number a bit.

Answer 2

Sorry, but scientists at Columbia University in1941 demonstrated that the human eye can seea flickering candle at a distance of 30 miles. Another more recent source shows that the human eye can see a 100 watt uncandescent bulb as 118 km, or over 60 miles.

Answer 3

Light A Single Candle

Answer 4

Idiotic answers. Ok, for those answers above, lets do this experiment. Take a loaded gun and place it to the head of the people giving these answers, held by a 20 something year old person with 20/20 vision, looking for the light of a candle at 30 miles, or 10 miles or 3 miles. Now, if the person holding the gun cannot see the candle, he must pull the trigger. Want to change your answers now?

Answer 5

from what i understand, the curvature of the earth is 7 miles from where you are looking on a flat surface such as the ocean. so.. that is as far as you can see.

Answer 6

what keith said


but since I dont have a better answer....time for...

Logic's Logic

the Palomar 200 inch could pick out a candle on the streets of London if not for the curvature of the earth.