" wrote in message
You are missing the efficiency. I high efficiency furnace consumes
1000kWh of energy and turns it into 970kWh of heat. A light bulb
consumes 1000kWh of energy into 200kWh of heat (I'm making up #s).
There is always energy lost in the conversion. A light bulb gives
off a lot of it's energy as light.

I agree; but where does that light energy go? It's my contention the light
is absorbed by the furnishings & surfaces & becomes heat. That kinda
illustrates the rationale behind my question. Because that light-heat
conversion isn't obvious, it only appears wasteful; but in reality, all of
the energy entering the house has to go somewhere; it doesn't "evaporate"
with no effect. Energy enters the house via the power lines. It leaves
through heat loss through the exterior surfaces. Energy in = energy out.
Light, fossil fuels, electricity; doesn't matter. Energy is energy. Leaving
a light bulb burning is just another energy input. Anything coming in that
route has to reduce the energy demand from other sources by an equivalent
amount. Yeah, it seems wasteful; but I can't justify that with the physics.

Joe F.