On Wed, 08 Jun 2005 20:58:15 -0400, Victor Roberts
wrote:

On 8 Jun 2005 15:17:29 -0400, wrote:

You might compare the bulb to a 60 W bulb using Bunsen's 1844 "grease spot
photometer"... move a 1" grease spot on a piece of white paper between the
bulbs until the spot disappears, which indicates the intensities are the
same at the card. The bulb brightness ratio is the square of the ratio of
the distance from the card to each bulb...

Nick

We are interested in lumens not brightness. And, since the size and
shape of the lamps in question are very different, we need to use an
instrument more sophisticated than a grease spot photometer. In this
case an integrating sphere or a goniometer will give lumen output
independent of shape..


Tell me again - why are we interested in lumens, not brightness?