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Date: 03 Nov 2007 18:18:28
From: Jim
Subject: Q: 3 watt Cree LED flashlight from Lowe's
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There was a thread on this a few weeks ago and one bit of information
didn't show up...
How much current do they draw? It gives some indication of how much
power it really is. I've seen "3 watt" flashlights that draw .09 amp
at 3 volts. In other words, they draw 0.27 watt. If we use a
generous 95% efficiency on the switching regulator about 1/4 watt goes
to the LED.
And the LED probably didn't come from a good bin, either...
Thanks!
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Date: 04 Nov 2007 12:16:39
From: Victor Kan
Subject: Re: Q: 3 watt Cree LED flashlight from Lowe's
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On Nov 4, 6:03 am, Jim <n...@email.com > wrote:
...
> So has anybody measured current draw?
Someone on candlepowerforums.com measured theirs at 1.2A, but I don't
recall if they measured what the voltage was, or what affect a voltage
boost circuit in the head might have. I think they were using the
included alkaline batteries.
I'd guess that they measured 1.2A @ ~3V, so maybe ~3.6 watts?
Have no fear about the adequate-ness of the beam from this light.
Even if you get one that isn't the best of the lot (I've had three of
these lights, one is great with a large, bright, white spot, the other
two, which I returned, had smaller, less bright, greener spots), it
blows away my Fenix L2D-CE turbo-mode output for bike use. The Fenix
is better as a general use flashlight though.
I'm using mine with 2650mAh AA cells in C-cell adapters and it's
working well for bike use, at least for my 40+ minute evening
commute. I haven't measured its max runtime though.
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Date: 04 Nov 2007 08:07:29
From: Jim
Subject: Re: Q: 3 watt Cree LED flashlight from Lowe's
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On Sun, 04 Nov 2007 12:16:39 -0000, Victor Kan <victor.kan@gmail.com >
wrote:
>On Nov 4, 6:03 am, Jim <n...@email.com> wrote:
>...
>> So has anybody measured current draw?
>
>Someone on candlepowerforums.com measured theirs at 1.2A, but I don't
>recall if they measured what the voltage was, or what affect a voltage
>boost circuit in the head might have. I think they were using the
>included alkaline batteries.
>
>I'd guess that they measured 1.2A @ ~3V, so maybe ~3.6 watts?
>
>Have no fear about the adequate-ness of the beam from this light.
>Even if you get one that isn't the best of the lot (I've had three of
>these lights, one is great with a large, bright, white spot, the other
>two, which I returned, had smaller, less bright, greener spots), it
>blows away my Fenix L2D-CE turbo-mode output for bike use. The Fenix
>is better as a general use flashlight though.
>
>I'm using mine with 2650mAh AA cells in C-cell adapters and it's
>working well for bike use, at least for my 40+ minute evening
>commute. I haven't measured its max runtime though.
Sounds good. Thanks!
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Date: 04 Nov 2007 06:36:05
From: Chalo
Subject: Re: Q: 3 watt Cree LED flashlight from Lowe's
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Jim wrote:
>
> There was a thread on this a few weeks ago and one bit of information
> didn't show up...
>
> How much current do they draw? It gives some indication of how much
> power it really is. I've seen "3 watt" flashlights that draw .09 amp
> at 3 volts. In other words, they draw 0.27 watt. If we use a
> generous 95% efficiency on the switching regulator about 1/4 watt goes
> to the LED.
>
> And the LED probably didn't come from a good bin, either...
The "3 watt" designation is the power rating for the Cree LED
emitter. It is not a measure of any specific qualities of the
flashlight in question, or even the quality of the LED.
Unlike an incandescent bulb, an LED can have good performance when
driven well outside its specification. Most white LEDs are even more
efficient when driven below their rated power than when they are
driven as specified. It is for this reason, as well as for marketing
reasons, that manufacturers sometimes choose to use an emitter with a
greater power rating than required for the application. The stated
wattage for such a light is often the LED's power rating rather than
its actual power draw in the device. 1-watt and 3-watt ratings are a
strong clue to that effect, those values being very common nominal
power ratings for high flux LEDs.
Chalo
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Date: 04 Nov 2007 06:03:27
From: Jim
Subject: Re: Q: 3 watt Cree LED flashlight from Lowe's
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On Sun, 04 Nov 2007 06:36:05 -0000, Chalo <chalo.colina@gmail.com >
wrote:
>Jim wrote:
>>
>> There was a thread on this a few weeks ago and one bit of information
>> didn't show up...
>>
>> How much current do they draw? It gives some indication of how much
>> power it really is. I've seen "3 watt" flashlights that draw .09 amp
>> at 3 volts. In other words, they draw 0.27 watt. If we use a
>> generous 95% efficiency on the switching regulator about 1/4 watt goes
>> to the LED.
>>
>> And the LED probably didn't come from a good bin, either...
>
>The "3 watt" designation is the power rating for the Cree LED
>emitter. It is not a measure of any specific qualities of the
>flashlight in question, or even the quality of the LED.
>
>Unlike an incandescent bulb, an LED can have good performance when
>driven well outside its specification. Most white LEDs are even more
>efficient when driven below their rated power than when they are
>driven as specified. It is for this reason, as well as for marketing
>reasons, that manufacturers sometimes choose to use an emitter with a
>greater power rating than required for the application. The stated
>wattage for such a light is often the LED's power rating rather than
>its actual power draw in the device. 1-watt and 3-watt ratings are a
>strong clue to that effect, those values being very common nominal
>power ratings for high flux LEDs.
>
>Chalo
That's right and that's why I want numbers before plunking down $30.
1 and 3 watt "ratings" are very common. So are .5, .3 and .25 watt
LEDs. And it doesn't matter what the LED size is if it is seriously
underdriven.
And then there is the matter of which bin the LED's came from. LEDs
from a good bin can produce twice the light as the low-rated bins.
So has anybody measured current draw?
Jim
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Date: 03 Nov 2007 19:37:05
From: A Muzi
Subject: Re: Q: 3 watt Cree LED flashlight from Lowe's
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Jim wrote:
> There was a thread on this a few weeks ago and one bit of information
> didn't show up...
>
> How much current do they draw? It gives some indication of how much
> power it really is. I've seen "3 watt" flashlights that draw .09 amp
> at 3 volts. In other words, they draw 0.27 watt. If we use a
> generous 95% efficiency on the switching regulator about 1/4 watt goes
> to the LED.
>
> And the LED probably didn't come from a good bin, either...
I'm not an expert but much puffery in bicycle lights claims "[as much
light as if it were an incandescent rated at] 3W"
--
Andrew Muzi
www.yellowjersey.org
Open every day since 1 April, 1971
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