LED Xmas lights

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Steve Kraus wrote:

Twice as bright is not really as much brighter as most people would expect. I would also guess that peak is important for the ability of the human eye to detect and that might reduce the effect even more. An interesting thought that. I wonder if anyone has done any studies on peak vs continuous light sensitivity of the human eye?
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Joseph Meehan

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Joseph Meehan wrote:

It is that way because the eye, and the ear, for sound, sees (or hears, for the ear), logarithmically. So, twice the sound or light will only appear as a small increase.
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True for hearing certainly but I have never heard of vision described that way. Decibels is a logarithmic scale but footLamberts is not.
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Steve Kraus wrote:

Well, I guess I was thinking F stops on lenses. I seem to remember that one F stop doubles (or halves) the light. Am I remembering this correctly?
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wrote:

Correct. Changing F-ratio by a factor of square root of 2 halves or doubles exposure.
- Don Klipstein ( snipped-for-privacy@misty.com)
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Steve Kraus wrote:

I don't know if anyone has done the testing, but I believe it is true for sight as well as hearing.
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I did a bit of experimentation. I posted results as well as comments on importance of peak brightness as opposed to average brightness of LEDs in:
http://www.misty.com/~don/ledp.html
There has been "conventional wisdom" that LEDs look brighter if you pulse them to increase peak brightness even if average brightness is unchanged. Optimum pulse frequency is barely fast enough to reliably make them appear continuously lit, although I have heard a few people say 100 Hz. The conventional wisdom there was that human vision had some "peak detection" effect.
This appears to me to have started in the early days of LED digital displays. It is true that the LEDs used in most of those looked much brighter with 50 milliamps at a 5% duty cycle than with 2.5 milliamps steady DC. However, the explanation is that those LEDs were nonlinear and more efficient at higher instantaneous current, and human vision averaged rather than peak-detected. Human vision's nonlinearity is largely after the averaging or "time integration" process.
- Don Klipstein ( snipped-for-privacy@misty.com)
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Current inrush when you plug this thing in could cause nasty sparking where contact is made and may be hard on the rectifier unless it's rated a good 3-4 amps or more. I would add a power resistor of a few ohms in series with the AC line. I would also add a fuse in case a voltage transient breaks down the rectifier or the capacitor fails.

The usual white LEDs have a blue LED chip coated with a phosphor that absorbs some of the blue light and fluoresces yellow light. The phosphor output is a fairly broad band from mid-green to mid-red in the spectrum, so white LEDs are not really horrible with color rendering.
- Don Klipstein ( snipped-for-privacy@misty.com)
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Kraus wrote:

The loss of 2 volts from the bridge rectifier may be part of the explanation. But I think a bigger part is that human vision is nonlinear, and doubling light output of a lamp does not make it look doubled.
Look at the lumens on packages of various wattages of lightbulbs. A "standard" or "soft white" 100 watt one produces close to twice the output of a 60 watt one, and that is almost twice as bright as a 40 watt one. A 100 watt lightbulb produces about 3.5-3.75 times as much light as a 40 watt one. Does it look that much brighter?
- Don Klipstein ( snipped-for-privacy@misty.com)
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