LED lighting for photo and video

Started Dec 14, 2011 | Discussions thread
Joseph S Wisniewski Forum Pro • Posts: 34,314
Nope, just deceptive spam...

Asmaa20 spammed dpReview with the same stuff he hit several other photo sites with:

New photo-shoot with LED lights. No need to use strobe any more, and you can see the end results before you take your photo or video.

Indeed. You can see how harsh and nasty the light is, deep, sharp shadows, and glare off that poor model's forehead.

What a horrible, horrible waste of some first-class makeup.

But, what you can't see "before you take your photo" is how badly you blew focus in the second shot. Now, from the EXIF, we can tell you were shooting a manual focus lens, apparently at an aperture too large for your focusing ability.

Although that sort of hard, edgy makeup cries out for smaller apertures and "cruel" sharpness.

But you needed ISO 800 to make this particular mess with your underpowered lights, so stopping down isn't possible.

http://bigcitylights.ca/blog/wp-content/uploads/2011/12/jacqueline001.jpg

http://bigcitylights.ca/blog/wp-content/uploads/2011/12/jacqueline017.jpg

These photos were lit by a single LED light bank and a reflector, and it gave very satisfying results.

The second shot is trash, and I wonder how the first would have held up full size, instead of web size.

Here are the LED panels we use at [spam url deleted] They are cheeper and lighter, and they have a very powerful out put.

No, they don't. That's just a 72 watt panel. The claim on that site that it's "the equivalent of a 1500W filament light" is pure deception.

High wattage filament lights have a luminous efficacy 23 lumens/watt for anything larger than 300W. So, 1500W of filament light is 34,500 lumens.

The 72W panel LED uses 1200 LEDs, that means

  • 28.75 lumens/LED (34,500 lumens/1200)

  • 0.06 W/LED (72W/1200)

That's a luminous efficacy of 479 lumens/W.

  • The best that has been done with 60mW t1-3/4 packages, the prefocused sort used in panels like that one is 85 lumens/W. (which makes the panel equivalent to a 250W halogen, not a 1500W, LOL).

  • The best that's been done with an LED in any form factor is a large, heat-sink mounted square 5 emitter chip, at 140 lumens/W.

  • A perfect light source that converts 100% of the electrical power you feed into it into a photographically useful spectral mix from 400-700nm (pure visible light, no wasted infrared or UV) has a luminous effacicy of 251 lumens/watt.

So, not only are these clowns claiming about six times better output than the LEDs that they're using are actually capable of producing, but they're also claiming about three times better output than any LEDs on this planet, and almost twice the output that it's theoretically possible to get from a "perfect" light source.

Next up, a device that lets your car run on water.

Now, here's the real rub...

You've got 72W of LEDs at an actual luminous efficacy of 85 lumens/watt, which is 6125 lumens.

The images, such as they are, were shot at 1/125 sec. That's...

  • 49 lumen-seconds.

That's "energy", the thing that makes pictures.

A common 15mm Xenon flash tube has a luminous efficacy of 40 lumens/W. Which means, you only need...

  • 1.22 Watt-seconds (49 lumen-seconds/40 lumens/watt) to produce the same lighting.

Except that even a speedlight like a Nikon SB-900 has a capacity of about 70 Watt-seconds. It can match the LED light when you turn the speedlight down 6 full stops. Or, you can shoot at f11, instead of (I'm guessing) f1.2 (why else a manual focus lens, but to use an old 50mm f1.2, in a desperate attempt to get something useful from that inadequate LED panel).

Heck, the popup flash on a D7000 is 5 W-s, or 4 times more energy than the LED panel.

And my studio strobes are 640 W-s.

You can also run them off a battery pack if needed.

4AA, like a speedlight that puts out 60 times the energy?

-- hide signature --

Rahon Klavanian 1912-2008.

Armenian genocide survivor, amazing cook, scrabble master, and loving grandmother. You will be missed.

Ciao! Joseph

http://www.swissarmyfork.com

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