Have you ever wondered why the newer compact florescent (CFL) and LED light-bulbs save electricity?
After all, if the lights are located inside the house their heat will warm that space, right?
Yes – and no.
The heat from regular light bulbs, cellphone chargers, stand-by electronic devices, and everything else using power does add indoor heat. Of course this is not helpful in the summer, but what about in the dead of winter?
It turns out that the extra heat is wasted when some of that light (accompanied with radiant heat) is lost through windows.
Where the light goes, so goes the heat. In fact, more than 95 per cent of the energy of that old light bulb is in the form of radiant heat, while only about five per cent is converted into light.
If you can see light from outside a building then you are seeing heat being wasted.
But since the light from all light sources is also lost through windows, why are the other lights better? It turns out that the hotter an object is relative to its surround-ings, the faster its heat is lost.
The filament of a standard 100-watt incan-descent light bulb burns at a whopping 3,000 C. Its heat loss is determined by multiplying 3,000 times 3,000.
That’s nine million units – a way bigger loss than from the far cooler CFL (about 60 C) and LED (about 30 C).
So, when the radiant heat and light from a white-hot light bulb is shining outside, it is efficiently and directly transferring its heat to your neighbourhood.
Thankfully, the more advanced windows contain coatings that reflect some of that radiant heat back inside, which is why they are much better than the clear single or double windows most buildings still feature.
This is why windows are often the No. 1 source of heat loss in homes. Unfortunately, even with the modern window coatings, a lot of the heat from those old bulbs is still lost.
That’s why closing your lined drapes or blinds make such a difference.
Most of the radiant heat emanating from the lights, furniture, coffee maker, our bodies, etc., is kept inside – where it belongs.
Don’t like your power bill? Try unplugging unneeded appliances, chargers, closing the drapes, and turning off or upgrading your lighting.
It’s a bright idea.
Ian Gartshore chairs the non-profit Energy Solutions for Vancouver Island.
