Perceptual psychologists have long been interested in limen – the threshold at which a stimulus becomes detectable. The following limen for the different senses, expressed in everyday terms rather than in terms of physical quantities, have a certain poetry to them. I got this information via email as a scan of an (unknown to me) textbook. I reproduce them here for your enjoyment:
Approximate absolute sensitivities, expressed in everyday terms:
Vision – A candle flame seen at 30 miles on a dark, clear night
Hearing – The tick of a watch under quiet conditions at 20 feet
Taste – One teaspoon of sugar in two gallons of water
Smell – One drop of perfume diffused into the entire volume of a three-room apartment
Touch – The wing of a bee falling on your cheek from a distance of one centimeter
Exact values vary between individuals and even from moment to moment with the same individual. Source: Galanter, E. (1962). Contemporary psychophysics. Holt, Rinehart, Winston.
Mind Hacks 
Very, very interesting.
AAAH! GETITOFF! GETITOFF! BEES!
30 miles for a single candle flame? That sounds excessive. Sure it’s not 3 miles?
Yep, 30 miles. That’s single photon acuity you’ve got in that there retina!
30 miles? I don’t know about you guys but on a clear night I can see from several million light years away
@Josh: I’m pretty sure most of what you’re seeing at that distance is slightly higher wattage than a candle. Inverse square law FTW!
Planck’s constant FTW, how far you can see is a question of how far light can travel. Way to ruin my joke though 😦