- #1
Insanity
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Trying to determine at what maximum distance a light source of a known lumen output can be seen in complete darkness. i.e. a 60W bulb or a single candle.
I known lux is the term for light intensity perceived by the human eye, but do not know what the lowest lux limit of the naked human eye is. One source I read said that after dark adaptation, the human eye can recognize objects in 0.007 lux1, but does not state if this is the lowest limit.
Given that 1 watt = 680 lumen2 (@ 555 nm) and 1 lx = 1 lm/m2, the lux at 1 meter would be.
total surface area = (4/3)*pi*r3 =~ 4.19 m2
lx = 680 lm/4.19 m2 = 162 lx
if 0.007 lx is the lowest limit, the distance at which the source would produce this is:
lm/lx = m2
lm/lx = (4/3)*pi*r3
((lm/(4/3)*lx*pi))(1/3) = r
((680/(4/3)*0.007*pi))(1/3) = r = 28.5 m
for a 60W bulb, the distance is:
((40,800/(4/3)*0.007*pi))(1/3) = r = 111.7 m
Is this correct?
Or is this the distance the light source produces enough light to recognize objects, and not necessarily the apparent brightness of the source? Or are these the same basically?
I apologize for the formulas, I don't know latex that well.
1Encyclopedia of Physics, Second Edition — ed. by Rita G. Lerner and George L. Trigg, VCH Publishers, Inc., 1991, p. 1342.
2American Institute of Physics Handbook, Third Edition, page 6-10
I known lux is the term for light intensity perceived by the human eye, but do not know what the lowest lux limit of the naked human eye is. One source I read said that after dark adaptation, the human eye can recognize objects in 0.007 lux1, but does not state if this is the lowest limit.
Given that 1 watt = 680 lumen2 (@ 555 nm) and 1 lx = 1 lm/m2, the lux at 1 meter would be.
total surface area = (4/3)*pi*r3 =~ 4.19 m2
lx = 680 lm/4.19 m2 = 162 lx
if 0.007 lx is the lowest limit, the distance at which the source would produce this is:
lm/lx = m2
lm/lx = (4/3)*pi*r3
((lm/(4/3)*lx*pi))(1/3) = r
((680/(4/3)*0.007*pi))(1/3) = r = 28.5 m
for a 60W bulb, the distance is:
((40,800/(4/3)*0.007*pi))(1/3) = r = 111.7 m
Is this correct?
Or is this the distance the light source produces enough light to recognize objects, and not necessarily the apparent brightness of the source? Or are these the same basically?
I apologize for the formulas, I don't know latex that well.
1Encyclopedia of Physics, Second Edition — ed. by Rita G. Lerner and George L. Trigg, VCH Publishers, Inc., 1991, p. 1342.
2American Institute of Physics Handbook, Third Edition, page 6-10