A topic commonly raised by proponents of a ban on incandescent lights is that the generated heat is wasted. In many areas (even in Australia), the heat is not wasted at all. It is in addition to other heat sources (radiators, reverse-cycle air conditioners, convection heaters, etc.).

Quite obviously, this doesn't apply when the outside temperature is 40°C (or even considerably lower), but even in temperate regions like Sydney, the little bit of extra warmth is perhaps usable for about 5 months of the year, or around 7 months in places like the UK. Small though it may be, having a 100W lamp switched on for a few hours will make some difference, even if only to make up for heat lost through window glass, ceilings, etc. In colder climates, the heat will hardly ever be 'wasted' - it is a usable form of additional heating for the home. Not much, but a number of people have brought this up on forum sites and elsewhere. It is not a 'silly' point as some have suggested. The heat does not simply go straight to the ceiling because hot air rises - most of the heat is radiated, and accompanies the light in exactly the same directions.

Any lamp that is outdoors wastes all of its heat output, so outside lights that are on for extended periods should be as efficient as possible. For a light that might be on for a few minutes every so often, the saving is obviously so small that it's of no consequence. For lights that are on for longer periods, you should ask yourself if they really need to be on at all. In many cases the answer will be no, so they should simply be switched off (too easy ).

Although rather trivial in the greater context, this is a point that has caused some fairly bitter disputes among experts (self appointed or otherwise). A document (apparently) exists that was produced by the 'Building Research Establishment' (BRE). In this, there was some information about the heat from incandescent lamps not being wasted at all. Unfortunately, I don't have the document or access to it, but there is another document [8] produced by the 'Lighting Industry Federation' (LIF), that attempts to refute the document from BRE. Without seeing both, it is obviously impossible to determine who is (or might be) right, but it is interesting that so much effort was spent to refute the argument. Much of the effort seemed to focus on the fact that most heat is radiated, so doesn't heat the air. Countless people in countless locations use electric radiators (bar heaters, or whatever other names may exist for them). We all know that they do manage to make us feel warm - this despite that fact that most of their heat is also radiated. No-one has claimed that incandescent lamps will replace heating, but their heat is not necessarily wasted when it's cold.

As to whether the "wasted" heat is more expensive that other forms of heating depends on what is used, where it is used, and many other factors. This small point could easily accommodate a full research programme, however, it is probably fairly trivial in the greater scheme of things. Some people use low power incandescent lamps to maintain a constant temperature for bird hatching - the heat is most certainly not wasted there. The same process is sometimes used to keep welding electrodes warm (and therefore dry) to improve weld quality, and no doubt many other examples can be found. CFLs have enough wasted heat themselves to perform the same duties, but temperature regulation is a lot harder to achieve. Just thought I'd mention that .

Most of the arguments (both for and against) the wasted heat issue are based on very limited existing data - limited because this is a new argument, and is without precedent. Mathematical extrapolation may be used to 'prove' that it is cheaper/more expensive to use supplemental heating, yet no real tests or trials seem to have been done to verify that the facts substantiate the claims. In a court of law, almost every argument either way would be thrown out as hearsay or conjecture, but no such limitations apply to people with a vested interest in the competing camps.