Candles Should Be Used For Heating, Not Lighting

By MUNGAI KIHANYA

The Sunday Nation

Nairobi,

12 February 2006

The demand for candles has started picking up as people get ready for the power rationing expected to begin in a few weeks. However, candles are not very efficient in lighting.

Almost all sources of light generate a lot more heat (over 90 per cent) than light. A typical candle produces about 40 watts of heat and only 12 lumens of visible light. Lumens are the units used for measuring brightness and a source emitting one lumen in all directions would be generating a total of about 0.018 watts of light energy.

Thus at 12 lumens, a candle generates only 0.22W (less than a quarter of a watt) in the form of light and 40 watts as heat. Compared to electricity, a forty-watt bulb produces 500 lumens of light. This is about 9W for the same total power consumption.

That is, to get the same brightness as a 40-W bulb, one would need to light up 40 candles. This would generate a total of 1,600 watts of heat, which is more than the output of the standard emersion heater. For this reason, it would appear that a candle should really only be used for heating, not lighting!

Now, an ordinary candle goes for about sh5, therefore, forty will cost a total of sh200. Compare that to the sh40 price of a light bulb and it becomes clear that candles are not at all cheap.

 Furthermore, an electric bulb has a life of about 1,000 hours. In that time, and at 40W rating, the bulb will consume 40 kilowatt-hours (kWh) of energy. At the current electricity price of sh9 per unit, 40kWh (units) will cost a total of sh360. Add this to the sh40 purchase price and the result is a total cost of about sh400 (purchase plus power consumed) over the life of the bulb.

How long does a candle last? Regular candle wax burns at the rate of 3.5 grams per hour. The ordinary candle weighs about 30g. Therefore the candle burns continuously for about eight hours. That is, 125 candles burned successively one after the other will last 1,000 hours. At sh5 each, the cost of 125 candles is sh625. This is more than the total cost (purchase plus power) of a bulb.

But remember, we need 40 candles to produce the same amount of light as one bulb. Thus we would need to burn 40 candles at a time, 125 times to fully replace the electric bulb. That is 5,000 candles, each costing sh5 to make a total cost of sh25,000!

If you thought electricity was expensive, think again.