Incandescent

"We live high up in the hills in the Scottish Borders, so when the lights flickered and then failed this week, we were well prepared. The wood burner was stuffed with logs, a pot of water was put to boil on top of it and I set off for a confab with the neighbours. As dusk fell, just after three, I lit the candles in the front room and settled back down to read. [...]
     It struck me that this was how people had read for almost all of the time that people have been reading: in darkness, slowly, concentrating, and more sensitive to the subtle interplay between what was on the page and what appeared to be on the page. In a sense, this was reading normally; reading with ample, white light was the exception."
— BOOKSBLOG, The Guardian
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"A LUMEN is a unit of measurement of light. It measures light much the same way. Remember, a foot-candle is how bright the light is one foot away from the source. A lumen is a way of measuring how much light gets to what you want to light! A LUMEN is equal to one foot-candle falling on one square foot of area.
     So, if we take your candle and ruler, lets place a book at the opposite end from the candle. We'd have a bit of a light up if we put the book right next to the candle, you know. If that book happens to be one foot by one foot, it's one square foot. OK, got the math done there. Now, all the light falling on that book, one foot away from your candle equals both…….1 foot candle AND one LUMEN!"
—TheLEDLight.com
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