How much light do you need to read in bed?

I know when it's enough but how do you measure it?

Well, the latest Levenger catalog has an interesting table which lists recommended lighting levels in foot–candles (fc) for various tasks.

I assume a fc is a unit based on the amount of light emitted by a standard candle from one foot away.

But I'm wrong: see the definition here.

Anyway, here's what the table said in terms of optimal fc for various applications:

• Reading in bed: 35–50

• Working at a desk: 40–75

• Reading in a chair: 60–75

• Close work: 100+

Keep in mind also that as you get older you require more light for a given task, since the pupil's ability to dilate decreases with age.

So much so that an 80–year–old requires six times more illumination than a 20–year–old to yield the same effective brightness at the retina in light–adapted conditions.

In the dark it's even worse: the 80–year–old retina receives 1/16 as much light as a 20–year–old's.

So now you know why older people tend to fall down the stairs much more frequently.

And you also can see why it was that your parents always nagged you about reading in the dark when you thought the light was just fine: both of you were right.

But I digress.

The lighting table was on page 19 of the catalog and was interesting enough in and of itself, but then on page 49 a reading lamp (60–75 fc recommended) was featured that had 84 LEDS (top) and was said to produce 110 fc.

The penny dropped.

84 into 110 = 1.31, so each LED produces roughly 1.3 fc.

Consider that for bedtime reading you need at least 35 fc.

1.3 into 35 = 27 LEDs MINIMUM are required for decent bedtime reading conditions/a good bedtime reading light.

So you can now see — I certainly do, with the scales finally cast from my eyes — why reading lights with 1,2,3, even 4 LEDs are pathetically inadequate no matter what else they might have going for them.

An array of ≥27 LEDs is not going to be a lightweight and it's gonna require plenty of juice.

But at least now we can see what needs to be done, and not fool around any more with wanna–be devices purporting to be "the solution."