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Measurement at home

# Candle power

## How powerful is a candle?

• Is the total power (light plus heat) of a candle more or less than for a typical domestic LED lightbulb?
• What is meant by ‘energy efficient lighting’?

Estimated time: 10 minutes + 2 hour wait between measurements.
No prior knowledge needed.

### Equipment required

• A new candle or tealight
• A match or other lighter
• Kitchen scales
• A clock or timer
• Paper and pencil for results and calculation.

### Risks

• Adult supervision as there is fire involved.
• Candles are hot and shouldn’t be left unattended.

## Steps

Watch the video

1. Use the kitchen scales to find the candle’s start mass (in grams). Write it down.
2. Start the timer or note the time as you light the candle.
3. Don’t leave candles unattended.
4. After 2 hours of burning, blow out the candle.
5. Use the kitchen scales to find the candle’s end mass (in grams). Include any wax that has spilled as we only want to count wax that has burnt. Write it down.
6. Do the following calculations to find the amount of wax used, chemical energy transferred and power:

Wax used (in grams)
= start mass (in grams) - end mass (in grams).
E.g. 14 g - 8 g = 6 g.

Chemical energy transferred (in joules) to both heat and light.
= wax used (in grams) x 43 000 (joules per gram)
E.g. 8 g x 43 000 J/g = 258 000 J

Power (in watts)
= energy transferred ÷ burn time (in hours) x 3600 (seconds per hour)
E.g. 258 000 J ÷ (2 x 3600) s = 36 W
7. Enter results below...

## Thoughts, tips and information

### SI measurement units

• Kilogram (kg) for mass
• Second (s) for time
• Candela (cd) for luminous intensity

### Challenge Topics

Measurement Science, Maths, Energy, Physics.

• Do all candles burn at the same rate? You can repeat this experiment with different candle types.
• Total candle power can be more than typical LED lightbulbs, though candles transfer most of their energy as heat, not light.
• Electric lighting was the first main reason electricity was brought into UK homes.