LED flashlight

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.

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

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.

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.

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.

On Jan 12, 11:50 pm, Benj<bjac...@iwaynet.net> wrote:

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.

On 1/13/2012 2:11 PM, Paul Cardinale wrote:

On Jan 12, 11:50 pm, Benj<bjac...@iwaynet.net>  wrote:
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.

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?