9. A single match or candle will light a room the size of a football stadium.

November 16, 2009

Indiana jones 1Action heroes such as Indiana Jones or even a film kid like Tom Sawyer who go into a cave, an abandoned house, a crypt or a catacomb light the entire place with one match or one candle. Is this real?tm sawyer

Now mathspigs, if you are interested in a career in stage/film lighting or even architecture you will need this maths.

light globe_tns60Watt light globe tells us how much power it uses. But some 60W globes are brighter than others. Light is measured with weird units.

candle_tnsUSA uses Foot-candles. Can you imagine the pickup line ‘You brighten up my world like a footcandle’? A foot-candle is the brightness of a candle 1 foot away. Now think of a bubble around the candle. Brightness is mostly measured using one square foot or one square metre of that bubble:

1 LUMEN = 1 Footcandle/ft squared

1 LUX = 1 footcandle/m squared

Don’t get too hassled by these units.  As a rough rule:

1 candle = 1 LUX

candle 1  Correction

candle 2 Correction 

candle 3 Correction

From graph you can see by 3m a Birthday Cake is not very bright even in a haunted house or crypt.

Challenge: Draw a graph of the brightness of your own Birthday Cake!

Big Challenge:Draw a graph of your Teacher’s Birthday Cake!!!!!! Ahhhh!!!!

We know:

1 candle = 1 LUX

Now compare the brightness of 1 candle to the brightness of other sources of light:

Family Living Room = 50 LUX

Toilet = 80 LUX

Office = 320 – 500 LUX

Indoor lighting Range = 50 – 1,000 LUX

Outdoor moderate sun = 32,000 LUX

Outdoor FULL SUN = 130,000 LUX

If you want sufficient light to live your everyday life you’d need 80 candles just to go to the toilet!!!!!!


  1. 80 candles in the toilet is what you’re used to. You can get by with far less than that. I’ve been in some enormous caverns with very little light, and you’d be amazed how well you can see. Sure, the movies exaggerate it, but not as much as you might expect from these numbers.

    • Hi Dr Mathochist, Quite so. Bathroom lights in restaurants, for instance, can be so bright many women want to run out the door screaming. It’s a mirror thing. I don’t know what happens in men’s toilets. Same as in dark caverns, perhaps. Cheers Mathspig.

  2. Bear in mind that a quarter moon gives roughly .01 lux, and this is enough to navigate a path or use a bathroom.

    • Thanks. More info welcome. Mathspig

  3. […] *Light Bulbs: Watts, brightness (lumens, inverse quadratic function) […]

  4. […] *Light Bulbs: Watts, brightness (lumens, inverse quadratic function) […]

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