# How many watts is a burning candle?

03 February 2008

## Question

How many watts is a burning candle?

## Answer

We had an answer on our forum from Bored Chemist. He pointed out that the original standard candle burned a waxy substance called spermaceti. It's called that because it comes from sperm whales.

The best that we have today is, of course, petroleum based wax. The standard candle, he says, would burn 120 grains of spermaceti an hour. That's 8g. Bored Chemist worked out for us that this means that it burns 2.16mg - or about 2 thousandths of a gram - of spermaceti every second.

If we know how much energy is in a gram of this stuff we can work out its wattage, which is essentially energy - in joules - per second of the candle.

Assuming that spermaceti is similar to a typical type of fat or oil, it's about 37 kilojoules (kJ) per gram. The candle was burning 2 thousandths of a gram each second which gives us a power of about 80 watts.

The reason it isn't as bright as an 80W light bulb is because it's really inefficient. Most of that 80W is actually given out as heat rather than light. So it's not like the energy-efficient light bulbs.

Most of the stuff coming off candles is heat. Only about 0.05% of the energy - so not very much at all - comes out as light.

## Comments

### Interestingly I googled this

Interestingly I googled this while sitting next to a glass teapot with a candle below it keeping it warm. When I read the question, I assumed the wattage referred to the heat energy not the light energy. Having burned myself on candles I think of them as sources of heat more than light.

### candle % energy light

Please provide a reference to 0.05% of a candle's energy given off as light.

### Um, about bulbs...

Re: "The reason it isn't as bright as an 80W light bulb is because it's really inefficient. Most of that 80W is actually given out as heat rather than light. So it's not like the energy-efficient light bulbs"

Um, light bulbs are extremely inefficient also, and give out most of their energy as heat. And who is using an energy-efficient light bulb that is 80 Watts! That would burn out your retina.

### Me...

I've got some high wattage energy efficient lamps; 80W is a perfectly reasonable rating.

### Candle light vs electricity

A "halogen" incandescent (hot wire) lightbulb is more efficient than without the halogen gas, but not in the same league as fluorescent and LED electric light. 80 watts of LED will comfortably light your yard.

An LED lightbulb may be labelled "80 watts" when it doesn't use 80 watts of electric power but it is offered as similar to a plain 80 watts incandescent lightbulb. Take it from me, this makes it easier for old people to pick the right lightbulb.

### Watts

But what is the equivalent light wattage? Maybe someone wants to use a candelabra. Your answer isn't very helpful

### Did you read the answer?

It tells you that the cancle is converting about 80W ("The candle was burning 2 thousandths of a gram each second which gives us a power of about 80 watts.")

Next it tells you "Only about 0.05% of the energy - so not very much at all - comes out as light."

Therefore you can find 0.05% of 80W to find the visible light "wattage" for the candle...

### Nah... It isn't 4W.

Nah... It isn't 4W.
At least according to what they said.

### Candle light

0.05 % of 80W is not 4W.

Not in this universe anyway

### Candle light math

Possibly they meant "5 percent or 0.05" for efficiency of a candle to produce light. That makes an 80 watts candle about the same as a 20th century 40 watts lightbulb if you take that to be 10 percent efficient. This feels about right to me.

"Explainthatstuff.com" claims that several dozen candles equal one lightbulb. But it will depend on the candle. The page also says that you can't compare "candela" to "lumens" exactly, and judges correctly that I don't really want to know why not. Not right now, anyway.

### candle light

I agree. I'm trying to find a light bulb that is the same brightness as a candle. I found a GE vintage style amber glass 5 watt bulb at Lowes that is good. How hard is it to just get an easy answer for those of us wanting a light bulb?

### Lamp / candle light

... and our grandma in the old Country would put a tall, clear glass cover over the oil lamp flame and the light would quadruple in size instantly. Enough to have light in the entire room. And we would all gather around those flames and tell stories and laugh. Talking about quality family time!! Interesting stuff!

### ehergy from a burning candle.

About 100 watts of heat is about right. It's interesting to note that is about the same as the heat from a human body or the heat that is needed to keep a cup of coffee hot.