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I'm trying to figure out how much LED stripe brightness I need to get roughly the same amount of light that would be produced by 4, 8, 12, 16 and 20 incandescent light bulbs consuming 40, 60 and 75 watts each.

I can't find any guides online which make sense for this, only the LED power supply wattage calculations, which is a step that goes after this.

  • If your wattage is in Energy Star certified which is a Daylight type color warmth then you could use the standard table for comparison but if your bulbs are of one of the other incandescent ranges the lumens can be affected. This is also true for bulbs like those stated to be long-life. And even the LED lights have color warmth ratings that affects the perceived brightness. – spicetraders Dec 25 '16 at 0:21
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You need to know the light output. LED strips (and other LED products) usually give this in lumens

Typical values for incandescent light bulbs are

Watts    Lumens
40       450
60       800
75       1000

Since LED products vary considerably in efficiency, I can't give figures for them.

To do this properly you need to understand the difference between luminous flux, luminous intensity, illuminance and other measurements.

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RedGrittyBrick covers incandescent lumens. For LED lumens on the cheapies, figure 60-100 lumens per watt.

A huge issue comparing them is that Incandescents and most other kinds light up an entire sphere, and those are the lumens they measure, even though we actually want a wedge or cone. Reflectors are not that efficient, so they waste a lot of their listed lumens. LEDs are directional and give light in typically a 140 degree cone. And that's still more than we actually want in most fixtures.

For instance I am under a downlight that emits about a 90 degree cone. Project that on a sphere (as the CFL is doing) and it's barely 10% of the surface area of that sphere. So 90% of the light is tossed into reflectors. I haven't run the numbers with a 140 degree arc, but it's many times better, and with lensing instead, near perfect.

For LED strips it generally means it gives you light exactly where you expect to get it, giving an LED lumen perhaps twice the punch of a lumen from any other source.

It gets even better when the LEDs are colored, because a native colored LED gives 100% of its lumens in the desired hue, whereas any other source there'll be a colored filter that blocks 2/3 of the lumens because they're the wrong hue.

  • Most LEDs quote lumens. Generally 100 lumens/watt is for the cool white bulbs. with warmer whites (closer to yellow/'traditional' incandescent bulbs) the lumens/watt falls – thelawnet Dec 26 '16 at 11:40
  • @thelawnet You're thinking of the orderly world of finished consumer goods with integral driver circuits, such as screw-in incandescent replacement "bulbs". These LED strips are the wild west. Not least be ause they are resistor regulated and those are sized for absolute worst case of a hyperactive automotive alternator running 14.2v. – Harper - Reinstate Monica Dec 26 '16 at 14:58

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