LED flashlight

[RichD]

I was looking at some LED flashlights, with ratings
from 50 to 150 lumens. A p-n junction is a p-n
junction, how do they get such varied outputs?

I examined the working end, they all look alike,
with a single bulb.


--
Rich

[Helmut Wabnig]

The more current you force through a p-n junction,
the more light will come out.
With veryvery much current, it will flash very brightly,
for a short duration.


w.

[Androcles]

"RichD" <r_dela...@yahoo.com> wrote in message
news:0706fb6b-ce41-4fac...@h7g2000pbs.googlegroups.com...

http://ptsurplus.yolasite.com/resources/SCR's.jpg
500 amp, 1600 V

A p-n junction is a p-n
junction, how do they get such varied outputs?

Does bigger and fatter mean anything?

I was looking at some incandescent lightbulbs, with ratings
from 40 to 150 watts. A tungsten wire is a tungsten wire,

[RichD]

On Jan 12, Helmut Wabnig <hwabnig@.- --- -.dotat> wrote:
> >I was looking at some LED flashlights, with ratings
> > from 50 to 150 lumens.  A p-n junction is a p-n
> > junction, how do they get such varied outputs?
>
> >I examined the working end, they all look alike,
> >with a single bulb.
>
> The more current you  force through a p-n junction,
> the more light will come out.
> With veryvery much current, it will flash very brightly,
> for a short duration.

Thay all use the same batteries, so it's as simple as
a series resistor? But then why does the higher
output cost more?

Also, there are flashlights which use multiple LED -
you can count them in the housing - why would the
manufacturers do that, paying for extra parts, rather
than using a single LED with high current? And
some of those multiple LED units cost less than
the single ones I checked.

Your reply seems too simplistic to be satisfactory -

--
Rich

[RichD]

On Jan 12, "Androcles" <H...@Hgwrts.phscs.Jan.2012> wrote:
> |I was looking at some LED flashlights, with ratings
> | from 50 to 150 lumens.  A p-n junction is a p-n
> | junction, how do they get such varied outputs?
> |
> | I examined the working end, they all look alike,
> | with a single bulb.
>

>  http://ptsurplus.yolasite.com/resources/SCR's.jpg
> 500 amp, 1600 V
> > A p-n junction is a p-n
> > junction, how do they get such varied outputs?
>
> Does bigger and fatter mean anything?
>
> I was looking at some incandescent lightbulbs, with ratings
> from 40 to 150 watts.  A tungsten wire is a tungsten wire,
> how do they get such varied outputs?
> I examined the working end, they all look alike,
> with a single bulb.

golly gee, you mean semiconductor manufacturers
make fat and thin LED chips, like GE makes fat
and thin tungsten wire? I did not know that!

ur a never ending edjicashun, Andro -

--
Rich

[ji...@specsol.spam.sux.com]

In sci.physics RichD <r_dela...@yahoo.com> wrote:
> On Jan 12, Helmut Wabnig <hwabnig@.- --- -.dotat> wrote:
>> >I was looking at some LED flashlights, with ratings
>> > from 50 to 150 lumens.  A p-n junction is a p-n
>> > junction, how do they get such varied outputs?
>>
>> >I examined the working end, they all look alike,
>> >with a single bulb.
>>
>> The more current you  force through a p-n junction,
>> the more light will come out.
>> With veryvery much current, it will flash very brightly,
>> for a short duration.
>
> Thay all use the same batteries, so it's as simple as
> a series resistor? But then why does the higher
> output cost more?

High power parts generally cost more than low power parts.

> Also, there are flashlights which use multiple LED -
> you can count them in the housing - why would the
> manufacturers do that, paying for extra parts, rather
> than using a single LED with high current? And
> some of those multiple LED units cost less than
> the single ones I checked.

Because high power parts cost more than low power parts and it is often
cheaper to use several low power parts than one high power part.

Also, when 1 LED out of a 10 LED array goes bad no one notices but if
there is only 1 LED it is pretty obvious if it fails.

That's the main reason the LED traffic lights are arrays.


--
Jim Pennino

Remove .spam.sux to reply.

[Sam Wormley]

On 1/12/12 8:52 PM, ji...@specsol.spam.sux.com wrote:
> Also, when 1 LED out of a 10 LED array goes bad no one notices but if
> there is only 1 LED it is pretty obvious if it fails.
>
> That's the main reason the LED traffic lights are arrays.

Is that what you think, jimp? Multiple LEDs so a failure won't be
noticed? Give us a break!

[Androcles]

"RichD" <r_dela...@yahoo.com> wrote in message

news:d77f17ca-8b55-4607...@s8g2000pbj.googlegroups.com...

I was handling 500 amp thyristors 40 years ago, Rich.
Hardly your bedside lamp dimmer switch when you need
accurate speed control of a large DC motor in industry, but
a pnpn junction is a pnpn junction, golly gee.

[Bob Pownall]

As Helmut said, you'll get different efficiencies depending how hard you
drive the LED.

Another thing to remember is "In theory, there is no difference between
theory and practice. In practice, there is." Yes, a PN junction is a
PN junction. Traps, radiative recombination centers, non-radiative
recombination centers, light extraction efficiency, and any number of
other things affecting the ideality of LEDs and are why LED
manufacturers employ engineers and scientists to make their product better.

Bob Pownall

[Benj]

As usual all the "science" people here have their heads up their
butts! God help us all if any of you work in any jobs beyond
McDonalds.,

A single "bulb" means nothing. it depends what is inside that "bulb".
In the old days a tungsten light bulb typically only had one filament
inside the "bulb", or if there were two (hi and lo beams for example)
only one was turned on at a time to prevent thermal issues.

But LEDs are tiny chips you can put a lot of them inside a "bulb". Now
the plastic domes you typically see usually only have one LED (unless
they are made to change color) but those flashlight "bulbs" are quite
different.

For one thing, they aren't single LEDs or even LEDS producing visible
light. What you can't see down in that bulb is an array of LEDs
surrounding a fluorescent dot. It is the Dot that gives all the light!
So really it's about so much MORE than simple LEDs in a battery
circuit, although they DO make those too. I've got one with about 100
leds in it. Nice.

[CWatters]

It's not trivial to manufacture a high power high efficiency LED. If it
was we'd all be using them for lighting our houses. Technical problems
limit how much of the electricity they convert to light and how long the
LED will last at a given power output.

There is also a law of physics, specifically the conservation of energy,
that limits how much light an LED can produce. You can't get more energy
out (in the form of light) than the energy you put in!

http://en.wikipedia.org/wiki/Luminous_efficacy

This has interesting implications for proposed products such as this
prize winning design..

http://www.sciencedaily.com/releases/2008/02/080220221822.htm

As an exercise work out how heavy the weight would need to be or how
high you would need to lift it to make the light work as claimed :-)

[Jeroen Belleman]

I'll bite: Let's assume a generous 100 lm/W for the LEDs. So we
have 6 W of power going into the LEDs. Over four hours, that's
86 kJ.

The thing is four feet high and there's a bit of height lost to
pedestal and top cover, so let's also assume the weight drops
1 m in those four hours. I'll lazily neglect all other possible
losses. So the mass will have to be m = E/gh = 86000/10 = 8600 kg.

Yep, looks like a real winner. Good luck turning that thing over.

Jeroen Belleman

[boxman]

There are several factors that contribute to the LEDs cost. Your base
assertion that a p-n junction is a p-n junction is entirely too
simplistic. A simple p-n junction composed of a single p layer with a
single n+ layer and ohmic contacts will not generate a significant
amount of light due to self absorption in the thick p-layer and the fact
that the recombination is not well confined resulting in low efficiency
of conversion from electricity to photons. These types of LEDs are easy
to make by diffusion and thus not very costly, but not a lot of light.

A high output led requires a heterojunction design and most high output
leds utilise a double heterojuction design. What that means is a
typical high output LED will start with a P type electrode connected to
a P GaN layer connected to a P AlGaN layer connected to a N InGaN layer
connected to another N AlGaN layer connected to a GaN buffer layer on
top of some substrate (usually sapphire, but Cree uses Silicon Carbide).
The n electrode is connected to the GaN buffer layer.
The thicknesses of the layers have to be precisely controlled to get the
proper wavelength output and the proper electrical characteristics which
demands a very complicated epitaxial growth process. Additionally, all
the different layers require careful processing to eliminate the stress
between the different lattice structures to prevent defects.

The result is an epitaxial growth process that can have very low yields
and wide variations in performance across the wafer substrate. When the
wafer is cut into the die pieces used for the individual LEDs, the die
pieces are checked for output and binned according to how bright they
are. The highest performing dies are consequently a small part of a
production run which leads to the more simple equation that low supply
and high demand = high price.

Hopefully that gives you some idea of how prices can vary so much for
LEDs and why high output LEDs cost more.

[hanson]

"Benj" <bja...@iwaynet.net> wrote:
As usual all the "science" people here in these NGs
have their heads up their butt's arseholes!
God help us all if any of them work in any jobs beyond
McDonalds....
>
hanson wrote:
10-4... ahahahahaha... LOL & ROTFLMAO...
Thanks for the laughs, Jacoby... ahahahanson



--- Posted via news://freenews.netfront.net/ - Complaints to ne...@netfront.net ---

[ji...@specsol.spam.sux.com]

Yep, that is exactly why LED traffic lights are made with arrays.

A failed traffic light is a public safety issue and must be fixed ASAP.

It costs a fair amount of money to send out a crew and truck to change
the lamp in a traffic light and it disrupts traffic, so minimizing
replacement is an agency goal.

If you ever get out of your bunker where you surround yourself with IPCC
reports and into the real world, look closely at the LED traffic lights
and you will often see failed LED's; the lamp assembly will be replaced
when enough have failed to make it worth the effort.

BTW, my source of information on this is registered traffic engineers;
what's yours?

[Paul Cardinale]

On Jan 12, 11:50 pm, Benj <bjac...@iwaynet.net> wrote:
> On Jan 12, 3:49 pm, RichD <r_delaney2...@yahoo.com> wrote:
>
> > I was looking at some LED flashlights, with ratings
> >  from 50 to 150 lumens.  A p-n junction is a p-n
> >  junction, how do they get such varied outputs?
>
> > I examined the working end, they all look alike,
> > with a single bulb.
>
> As usual all the "science" people here have their heads up their
> butts! God help us all if any of you work in any jobs beyond
> McDonalds.,
>
> A single "bulb" means nothing. it depends what is inside that "bulb".
> In the old days a tungsten light bulb typically only had one filament
> inside the "bulb", or if there were two (hi and lo beams for example)
> only one was turned on at a time to prevent thermal issues.
>

Perhaps you haven't heard of 3-way bulbs.

[CWatters]

On 13/01/2012 14:41, Jeroen Belleman wrote:

>> As an exercise work out how heavy the weight would need to be or how
>> high you would need to lift it to make the light work as claimed :-)
>>
>>
>
> I'll bite: Let's assume a generous 100 lm/W for the LEDs. So we
> have 6 W of power going into the LEDs. Over four hours, that's
> 86 kJ.
>
> The thing is four feet high and there's a bit of height lost to
> pedestal and top cover, so let's also assume the weight drops
> 1 m in those four hours. I'll lazily neglect all other possible
> losses. So the mass will have to be m = E/gh = 86000/10 = 8600 kg.
>
> Yep, looks like a real winner. Good luck turning that thing over.
>
> Jeroen Belleman

..and even if the LED was 100% efficient it would still be too heavy.

[RichD]

On Jan 12, j...@specsol.spam.sux.com wrote:
> >> >I was looking at some LED flashlights, with ratings
> >> > from 50 to 150 lumens. A p-n junction is a p-n
> >> > junction, how do they get such varied outputs?
> >> >I examined the working end, they all look alike,
> >> >with a single bulb.
>
> >> The more current you force through a p-n junction,
> >> the more light will come out.
>

> > Thay all use the same batteries, so it's as simple as
> > a series resistor? But then why does the higher
> > output cost more?
>
> High power parts generally cost more than low power parts.

While that is generally true, in this case we're talking
about a few watts, not an oven. The housings are
all the same. Maybe one uses #20 gauge wire,
and another #18, but that isn't going to explain a
$3 price difference.


--
Rich

[RichD]

On Jan 13, boxman <box...@voyager.net> wrote:
> >>> I was looking at some LED flashlights, with ratings
> >>> from 50 to 150 lumens.  A p-n junction is a p-n
> >>> junction, how do they get such varied outputs?
> >>> I examined the working end, they all look alike,
> >>> with a single bulb.
>

> There are several factors that contribute to the LEDs cost.
> Your base assertion that a p-n junction is a p-n junction is
> entirely too simplistic.

> ......

> The result is an epitaxial growth process that can have
> very low yields and wide variations in performance across
> the wafer substrate.  When the wafer is cut into the die
> pieces used for the individual LEDs, the die
> pieces are checked for output and binned according to
> how bright they are.  The highest performing dies are

> consequently a small part of a production run...

> low supply and high demand = high price.
>
> Hopefully that gives you some idea of how prices can vary
> so much for LEDs and why high output LEDs cost more.

Thanks, that's my idea of a substantial reply.


--
Rich

[ji...@specsol.spam.sux.com]

In sci.physics RichD <r_dela...@yahoo.com> wrote:

Point totally missed.

It is the cost of making high power LED's versus low power LED's.

Making a high power LED is a lot more complex and expensive than making
the filament of an incandescent lamp bigger and the production yield for
the high power devices is lower.

[be...@iwaynet.net]

What? You want be to give you all a complete education for free? You
have any idea what the word "typically" implies? Yes, and stop light
bulbs have two filaments which if your tail lights are on (at night) and
you stop, they BOTH come on. But it is not a "typical" Edison bulb.

So what does this have to do with high powered LED flashlights being
fluorescent while all you guys are talking about PN junctions and their
currents?

[Paul Cardinale]

Are you too stupid to understand what YOU wrote?
You used the word "typically" referring to to single filament bulbs,
not double filament bulbs.
And you wrote " if there were two (hi and lo beams for example) only

one was turned on at a time to prevent thermal issues. "

Which is not generally true, and wouldn't even be true if you had
inserted the word "typically".

Paul Cardinale