[chc]

That's noisier, but it isn't a louder signal. We're talking about detecting alien species across vast distances. You can't do that by looking at a planet's light pollution AFAIK, because giving off this level of light is just not very notable — the sun reflecting off our planet is much brighter.

[fivedogit]

But sunlight reflecting off a random planet (including ours) is not useful. Sure, you can detect it, but it doesn't say anything about whether the planet has intelligent life or not. It would just be noise in the cosmos, no signal.

I'm not a physicist, but my understanding is that all EM frequencies -- visible light, radio, infrared, etc -- travel away from earth at the same speed (c). Since space has (almost) nothing to slow them down, then they'll just keep going forever. Thus, "strength" (however you want to measure it) is largely irrelevant so long as the signal it produces is detectable apart from all the other outgoing information. So the "light" broadcast from a TV tower is the same as the light from a spotlight at a shopping mall, in terms of its ability to travel through space and get noticed by aliens.

The only exception I can think of would be our atmospheric interference. Some light may penetrate our own cloud layers better than others. So all light may not be created equal, in that sense.

[chc]

The GP was talking about how we're quieter now (i.e. using lower-powered radio signals), and you replied that we're louder because we have a lot of light pollution nowadays. My point was that AFAIK light pollution does not produce a signal for detecting life. We're producing louder noise and a quieter signal.