Indeed, this effect is not a given, specially if the resource is scarce to begin with. But regarding your example, personally, I'm actually kind of "keep addin

Indeed, this effect is not a given, specially if the resource is scarce to begin with. But regarding your example, personally, I'm actually kind of "keep adding light bulbs" thanks to LEDs. I'm no longer using one central 75W incandescent bulb per room, but rather 4 or 5 Philips Hue lights (bulbs & led strips) in an indirect fashion. Hue bulbs & these new usages would not have existed without the LED efficiency gains. This counter example, of course, has many flaws, firstly, it's only my specific situation, not an average case. The efficiency gains (energy and longevity) is only part of what enabled these new types of lights. And lastly, I think my energy consumption is still lower non-the-less. But it demonstrate how things might not be so clear cut.