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LED dimming performance: Incandescent vs Cree 4-Flow vs Philips

LED dimming performance: Incandescent vs Cree 4-Flow vs Philips

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I used the Cree as a "typical" LED lamp, and the Philips since it was designed to emulate an incandescent, with yellow emitters for when dimmed and a large capacitor for fade.

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Date added:Feb 15, 2016
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Ash
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Feb 16, 2016 at 10:44 AM Author: Ash
With the Incandescent, a plot of "dimmer position vs lamp output" would actually have a "loop" near the bottom end :

When dimming down to 0 slowly, the filament is hot and its resistace is high. The power dissipated on it (averaged) is sufficient to keep it deep red incandescent

When dimming up from 0 slowly, the filament is cold and voltage drop on it is low - too low to dissipate sufficient power to heat it up

So, there is a region that if you reach it on the way down the lamp still lights deep red, but if you reach it on the way up the lamp is cold and not lighting

I guess that happens at the low voltages, where the resistance of the cold filament vs. resistance of dimmer components in "ON" state make a significant divider, so not all the line voltage really goes to the lamp even with the thyristor is allready ON
rjluna2
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Robert


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Feb 16, 2016 at 10:51 AM Author: rjluna2
@Ash: Sounds like Hyteresis curve for the incandescent light bulb. I must have played around with the incandescent light bulb and the dimmer thousand times

https://en.wikipedia.org/wiki/Hysteresis
https://he.wikipedia.org/wiki/%D7%94%D7%99%D7%A1%D7%98%D7%A8%D7%96%D7%99%D7%A1

Pretty, please no more Chinese failure.

Medved
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Feb 16, 2016 at 11:05 AM Author: Medved
Even when the lamp is cold and you apply e.g. 10deg of phase angle, it will settle on exactly the same temperature as when it is initially hot. It just needs few seconds to settle, but it does settle on exactly the same temperature, so brigtness.

The "loop" (or hysteresis) you may observe when playing with dimmers does not come from the lamp (that really does not have any at all - assume you are changing the set level slowly), but it is caused by the functionality of the simple dimmers alone (you need a more complex design and/or a digital dimmer to eliminate that problem).
Turning the pot down means you are reducing the power really smoothly to zero. But when zero and you turn it back, the dimmer stays at zero output power. You have to reach the position corresponding to about 32degrees of phase angle for the dimmer to "wake up" and it then immediately jumps to that phase angle.
This phenomenon comes from the RC+diac trigger circuit, the phase angle depends on the diac Holding versus Trigger voltages, it could be calculated as cos(Vhold/Vtrigger); for 33V diacs with 5V snap back (so the Vhold being 5V lower than the 33V of Vtrigger) it is the 32deg.

No more selfballasted c***

mdcastle
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Feb 16, 2016 at 05:29 PM Author: mdcastle
The method I used was to enter the desired power to be supplied in my computer, which controlled the electronic dimmer. Then I read the output on a light meter a few inches from the lamp. So it was at a given power level long enough for the filament to stabilize.
Medved
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Feb 17, 2016 at 02:03 AM Author: Medved
But how the dimmer was implemented?
Did it used really a digital timer, or a standard RC+diac+triac with the R replaced by an LDR or optocoupler controlled by a LED current coming from a computer controlled DAC (quite frequent implementation I have seen - simple and works quite well; the hysteresis). The second works exactly in the same way as with the mechanical knob, include the hysteresis.

No more selfballasted c***

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mdcastle 26956281@N02
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Feb 17, 2016 at 10:40 AM Author: mdcastle
I'm not sure- the dimmer is just a standard triac based dimmer except for the fact that you can use a computer to set it at whatever power level you want, so you don't need to guess by twisting a knob.
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