I'd imagine on the whole it's wasted. Half the year they aren't just generating wasted heat, they're increasing cooling costs. The half of year that the heat is wanted, it's usually above you, and I imagine that heat is being generated less efficiently than a purpose-built device.

> that heat is being generated less efficiently than a purpose-built device.

“efficiency” is meaningless when heat is desired. if you pump 100W into a device, and it “wastes” all that power, you have successfully generated 100W of heat. only heat pumps can be more efficient.

"only heat pumps can be more efficient"

Exactly. And if you have a whole house/apartment electric heating system it is very likely that it is in fact heat pump based. So you are better off using that for heat than the lights.

If your whole house/apartment heating system is gas or oil based, that will probably be even cheaper than the heat pump electric version.

>if you have a whole house/apartment electric heating system it is very likely that it is in fact heat pump based

Hmm, where? I have never knowingly been in a house with a heat pump in the UK, and lots of cheaper flats have electric radiators and immersion heaters.

Finite fossil fuels... which might not even be "environmentally cheaper" in the long run...

Not quite – some energy was lost converting from its source form to electricity. If you heat your house by directly burning natural gas (the most common way in cool countries like the UK) then it can still have an efficiency advantage over converting electricity to heat.

The fossil fuel infrastructure (even disregarding extraction), is not zero cost either.

This is true but - especially if your house is not well insulated - getting heat in the right place matters too - most people don't need to heat their roofs or ceiling spaces. There's also a more minor point on time of day you want heat or not.

Well, hot air tends to rise anyway.

Anyway, my point is that the inefficiency lost to "waste heat" is not 100% waste.

The only thing that can be more efficient is one of the most common forms of heating devices.

During the summer, it's also extra inefficient to pump 100W into a device producing heat and then pump even more power somewhere else to cool down the room.

There's a lot more people that use heating than cooling (in Western countries at least).

Although heating with gas will produce different amounts of CO2 than heating with electricity.

I had a friend with a condo in Chicago with a 400-500 dollar a/c bill plus another 200-300 year round bill because the builders hated the earth and universally used halogen bulbs. But on the plus side the heating bill was probably 50 bucks for the year.

How does it compare to similar buildings nearby ? (Most people don't use a/c.)

> I imagine that heat is being generated less efficiently than a purpose-built device.

All the heat that comes out of a lightbulb is being generated at 100% efficiency :)

(Although it's likely more expensive to heat your home electrically instead of via natural gas)

Heat pumps have higher than 100% efficiency because they extract heat out of air / water. 100% is a very low efficiency for electric heating. Anything lower than 400% is considered below average.

Sadly, heat pumps are still very rare. (They're much harder to do properly than just electric heating.)

Resistive heaters are very low efficiency when compared to heat pumps. How much more efficient depends on the climate you are in, of course. So, in net, they require more cooling in the summer, and the heat they provide in the winter is more expensive than the heat pump that you are likely to be using (in a home anyway).

During cold winter months, when one is otherwise attempting to add heat to the indoors, the 'waste' heat from incandescent bulbs is not really 'wasted', since it contributes slightly to maintaining the interior room temperature.

If they are resessed down lights you mostly end up heating roof or ceiling space. And in summer not only do you consumer power for heat you don't need, you end up consuming power to remove said heat with AC. Also in winter there are much more efficient ways to heat than electricity, such such as heatpumps.