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Error in recent TAG
I'm sure everyone has received the recent TAG by now. I was browsing
through the past week's APDs to see if anyone was going to correct the
glaring error in the Q&A column but I guess you were all politely
waiting for me <g>.
In the response to "DS" from Ft. Collins about the percent light loss
with distance from a fluorescent bulb, the technical editor dropped
the ball completely. Remembering only the "Inverse Square Law" and
not the conditions that accompany it, she created a table that showed
99% of the light is lost 36" from a fluorescent bulb. BZZZT! Thanks
for playing but that's NOT the right answer. If such a thing were
true, fluorescent lights would not be very useful for general lighting
where they are typically 5 to 8 feet from things they illuminate.
The inverse square law (light intensity decreases with the square of
the distance from the light source) applies to a point source
radiating in all directions. It does NOT apply to a linear source or
to a source with a reflector. In this case, in practical applications,
the loss is roughly inversely proportional -- twice the distance, one
half the light. This depends greatly on the on the reflector. Over
short distances, the "loss" is due to spreading of the light pattern
-- the light does not disappear. Once light enters the water, loss is
caused by other factors.