Here’s a puzzling question that Matt Trawick asked me today. (By the way, I also lifted the title of this post from him.)
In a comparison of incandescent bulbs with compact fluorescent lights (CFL), the government tells us that
Incandescents also project light further [than CFLs].
The question is simple: What could this possibly mean?
Obviously one bulb will seem to “project further” than another if it’s brighter, but this seems to mean something different: they’ve already talked about the comparison of brightnesses, and then they raise this as a separate point. So it seems to mean that, for equal brightness (however that’s defined), the incandescent projects further. Matt and I can’t think of a sense in which that’s true.
Matt says that this claim is widespread on the Web. Here’s another example, which may shed light on what’s meant:
Since the light source is a single point, incandescents also project light further than CFLs that project a more diffuse light.
As far as I’m concerned, this just makes things worse. If “A projects further than B” means anything, it must mean this: if the two bulbs have equal apparent brightness when seen up close, then A looks brighter than B when seen far away. But by that definition the diffuse source will project further than the point source.
(The reason is that the point source intensity dies away like the inverse square of distance, but the diffuse source dies away more slowly. At large distances, the difference will be small, but it always works in favor of the diffuse source.)
So does anybody know what this claim means?