The sound power in dB does not change with distance because the power emitted by a source is a measure of the total energy (over time) emitted in all directions. A 100 watt light bulb's candlepower output analogous to a speaker system's acoustie pouver output remains the same, regard- less of the distance from which one observes it, but the light intensity analogous to SPL) does fall off with distance. The brightness of light falling on a given surface de- creases as distance increases from the bult, just as SPL falls off with