Lightbulb Brightness (re: Distance of Celestial Bodies)

Cecil's Columns/Staff Reports
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On 07-Nov-2000, Chronos wrote in his answer to, “How do
they figure the distance between celestial bodies?”

The apparent brightness of an object depends both on
how bright it actually is, and on how far away it is.
For example, if a hundred watt light bulb is 10 meters
away, it’ll look exactly as bright as a 25-watt light
bulb 5 meters away.

I just wanted to point out that the assumption that a
100-watt light bulb is not four-times “as bright” as
as a 25-watt bulb. That is, lumens per watt is not
constant as wattage changes. This is especially true
when considering different types of bulbs, e.g.
incandescent versus fluorescent, but is also true for
a 25-watt incandescent versus 100-watt incandescent.

Go to your favorite web search engine and do a search
on “watts” and “lumens” for any number of references
on the topic. Or go to the utility closest and look at
the wattages and luminosity numbers printed on the front.

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The original column: How do they figure the distances between celestial bodies?
It’s a good idea to include the link, so that we can make sure that everyone’s on the same page, and so CKDextHavn doesn’t yell at you.

As for your comment, how about if I weasel out and say I was refering to bolometric luminosity, which is totalled over the entire electromagnetic spectrum? Neglecting the amount of heat that’s lost via conduction and convection, that’ll be exactly equal to the wattage of the bulb. You do have a good point, though, I should have been a little more careful with that when writing it (and would have been, had I realized that there was such variation).