Will a CFL light bulb and an incandescent light bulb, in separate respective closed systems, produce exactly the same amount of overall temperature increase over time?
Assume you have two identical closed systems with gray walls, with a system input of 20 watts of power each.
EDIT added for clarity: (On the packaging of the CFL light bulb the large print equivalent wattage is irrelevant… the input current of both bulbs is a consistent 20 watts of power each. The comparison wattage vs. the actual wattage of the CFL is off subject.)
One has a CFL, one has an ordinary incandescent light bulb. Will both systems increase in heat the exact amount, every hour?
Due to conservation of energy it shouldn't matter if one light source is more efficient, right?… it's the same amount of energy input. One light makes more heat one makes more light, but the light when it hits the gray wall is converted to heat, right?
There is no such thing as loss of energy… it's just converted to another form of energy… and light is converted to heat, right?
The back story of this question is my wondering that if my wife leaves an incandescent light bulb on in the winter time it's not so bad because even though no one is in the room it's still heating up the room. On the other hand if she leaves on a CFL it's more efficient but it should still add heat to our "system," i.e., our home.
Best Answer
No they won't
if you're reading the "watts" off the package.
That is because for an incandescent bulb, the "60 W" is a measure of the actual electric power it dissipates. Most of that power is thermal (i.e. heat) from the get go, and every last Watt ends up heating in the room eventually (when the light energy thermalizes).
On the other hand, CF lamps and LED lamps are labeled with "light output equivalent" wattage, because the first thing people care about when buying a bulb is how much light they're going to get and we've grown used understanding that in terms of an incandescent bulb's total power dissipation (I suppose that in twenty years this will look like a really stupid convention to the kids). If you read the package closely you'll see that high efficiency lamps generate about the same amount of light, but much less heat. The relationship is not linear in equivalent wattage, but runs about 1/7 for CF bulbs in the 60--120 "Watt" range.
Yes they will
if you really mean, that each bulb dissipates 20 Watts.
However, that's a really dim incandescent bulb suitable for little more than a night light, but a pretty good CF bulb suitable for keeping a medium sized room well lit and allowing you to read comfortably.