Yet another geek blog

13 January 2009

Fluorescent with Rage about CFL Bulbs

Incandescent light bulbs increase your heating bill.

My New Years resolution was to stop getting would up about idiotic science stories in the press. But if I read one more time that incandescent light bulbs reduce your heating bills then they will be able to plug me into the national grid.

The Daily Mail has declared war on energy efficient light bulbs and this bizarre myth seems to be everywhere:

It was even reported as a fact in a pro-CFL article in the Guardian, although here it was only thought to be true if no lampshades were used.

So Here Comes the Science Bit

  • Incandescent bulbs are energy inefficient.
  • Therefore they are hot.
  • Therefore they heat your room.
  • Therefore your heating system needs to do less work.
  • Therefore, (if we ignore the cost of running the bulb), your bills are lower.

The bit in brackets you will only read here.

What does 'Efficiency' Actually Mean?

It can mean many things. In this context, it is a measure of how much of what you want you get for your money. So, I have a bar-heater and a light-bulb and I measure how much heat and light they give me for every pound I put in to the meter. My bar-heat gives me 10 units of heat and 1 unit of light and my light bulb that gives me 1 unit of heat and 10 units of light.

What is the cheapest way for me to heat my room to 20°C? Obviously the bar-heater is 10 times cheaper. So, for the very lowest bill possible, 100% of my heat must be bought from the cheapest source. If any of my 20°C is bought from anything but the cheapest source then the cost will be higher. The hotter my bulb becomes, the more of my 20°C will be provided by it and the higher my bill will be.

I need to spell this out:

Heat from anything but the cheapest source can only increase the cost.

So Why the Confusion?

I can only imagine that people somehow believe that the heat from a bulb comes free with the light.

The lamp shade idea is presumably caused by the fact that you cannot directly feel heat being radiated through a shade. But the bulb is heating the shade and the shade is heating the air so all the heat is still there.


posted by Yet Another Geek @ Tuesday, January 13, 2009


If you use Firefox, and install Adblock, you miss out on this stuff: