" wrote in
:

On Sun, 26 Dec 2010 16:02:42 -0500, wrote:

On Sun, 26 Dec 2010 12:41:26 -0600, "
wrote:

Probably parallel strings of LEDs.

*Series* strings. Parallel does nothing but cause more trouble. ;-)

OK the science comes fast around here
I took a flashlight apart.
It appears they use a 4.5v LED, 9 in parallel with NO resistor at all.
The internal resistance of 3 AAA cells seems to be the limiter

I've seen that too; a very poor design. There is nothing to
current-share across the LEDs. Counting on the internal resistance of
a battery is really ****-poor.

With just the batteries in there the lights are pulling about 244ma
(they are fairly new batteries)
This is hurt your eyes bright.
I put my 1k pot in there and even all the way off I am dropping .05v,
current around 211ma.

I assume you mean, "all the way *ON*", as in "zero" ohms (the wiper
resistance is about 1/4ohm).

don't forget the meter resistance,too.

--
Jim Yanik
jyanik
at
localnet
dot com

" wrote in
:

On Sun, 26 Dec 2010 15:17:19 -0500, wrote:

On Sun, 26 Dec 2010 11:49:47 -0600, Jim Yanik
wrote:

LEDs can pop very fast when overdriven.(as the rheostat guy will
discover)

Since the rheostat will be in series with the proper "full load"
ballast resistor, overdriving is not an issue. Current is going to be
dropping as a square of the change in resistance and so will the heat.
As long as the rheostat is rated as high as the ballast resistor,
where is the possibility of a problem?

High power rheostats aren't all that common, or cheap, these days.

I suppose the open question is, how big is the resistor in a
commercial lamp?

I haven't seen a lamp with a rheostat is decades.

In my case it doesn't matter at all since I will be driving mine from
a wall wart. I am tempted to just take a cheap 4.5v LED flashlight
apart (a couple bucks at H.D) . That is probably cheaper than I can
buy 9 LEDS and for my purposes, it provides plenty of light. I just
want to spread them out a bit. I even have a 4.5v wall wart.

If you're powering this thing with a DC wall wart, simply PWM the
thing. For less than a buck or two in parts, you're all done, and you
can forget about the rheostat and waste heat.

his wallwart may burn them out,if it can supply more current than the LEDs
can handle;there's no limiting resistor.

--
Jim Yanik
jyanik
at
localnet
dot com

In , zzzzzz wrote:
On Sun, 26 Dec 2010 23:56:01 +0000 (UTC), (Don
Klipstein) wrote:

In , zzzz wrote:
On Sun, 26 Dec 2010 21:31:57 +0000 (UTC), (Don
Klipstein) wrote:

One more thing: For outdoor or basement nightlighting or security
lighting, I strongly recommend that any white lights (LED or otherwise)
be of cooler color (more bluish, higher color temperature). This is
because night vision is significant in such dimmer lighting environments,
even if colors and sharp outlines are visible. A spectrum richer in
mid-green to mid-blue favors greater illumination in this case.

For indoor, basement, indoor security, and night-lights, I'd think you'd
want more of a red so you don't spoil your night vision. ...or maybe a
white photo-flash and cover *your* eyes, while the no-good gets blinded.
;-)

I've tried all sorts of things for seeing around with little light.
My experience says to make use of night vision. A cool white LED can
illuminate a room to extent that I can walk around and see everything,
using a couple to a few percent as much light as if I used red light.

That's interesting and a bit counterintuitive. I can see fine around the
bedroom, at night, with only the backlight of my XM radio but it's quite
bright. I guess it's not enough to trigger the iris but still make use of the
higher sensitivity wavelengths. OTOH, for astronomical viewing (and
submarines one uses red lights.

Oh yes, I do remember my stretch of time when I was into astronomy.

Red lights were used to see things other than stars, such as star maps,
so as to see in high resolution (from photopic vision) with light that
does not overload and reduce sensitivity of scotopic vision.

I would think the requirements of nightlights are usually different. I
don't see the need to be able to read a newspaper - only to recognize it,
to be able to read the name of the newspaper. There is also the fact
that I don't mind having my night vision attenuated a bit by using a light
that makes use of it for this purpose. I have some green and blue LEDs
that can illuminate a largish living room that well to me with maybe .1
milliamp (and full dark adaptation), though I would only count on low
current performance good enough to do that with .25 milliamp.
--
- Don Klipstein )

In , Jeff Thies wrote in part:
On 12/26/2010 4:31 PM, Don Klipstein wrote (in part)
Lots of editing for space

One more thing: Most white LED units claiming 100,000 hour life
expectancy, especially cheaper and non-major brand ones, significantly
fade in 4,000 to 50,000 hours. I generally recommend green or blue LEDs
for nightlights. Any LED "security lighting" that must be at least
basically white should be by or have LEDs made by *major* brands of
"lighting grade" LEDs, such as Philips/Philips-Lumileds, Cree, Nichia,
Osram/Sylvania, Citizen/Cecol, and the like.
Also, the usual "bullet shape" low power LEDs are unlikely to get past
10,000 hours before significantly fading if they are white unless they are
greatly underpowered.

Thanks for joining in. I hope it is more joy than aggravation. I take it
that the failure is with the phosphors and not with the junction
generating the UV? Interesting as most of us had been thinking of LEDs
as being forever. I have noticed that many of the new LED traffic lights
have sections out. I don't know whether that is a circuitry break or
whether an LED actually failed. In the environment they are in I would
think connection failure from thermal cycling. Either internal or external.

White LEDs fade mainly, almost entirely, from the phosphor degrading.

BTW, the usual white LEDs have phosphor over blue LED chips, not UV
ones.

I am also noticing many LED traffic lights with some LEDs out. That
appears to me to be, as you say, broken connections. I don't know where
they're breaking. One thing I notice is that affected LEDs are
disproportionally at the edges of the traffic lights around where I live.
This makes me suspect stress concentrated at the edge of a PCB that the
LEDs are on, so I wonder how well the PCBs are fitted to what they are
mounted to.
--
- Don Klipstein )

On Sun, 26 Dec 2010 23:02:08 -0500, wrote:

On Sun, 26 Dec 2010 21:17:20 -0600, G. Morgan
wrote:

(Don Klipstein) wrote:

Brightness of LEDs is controlled by how much current flows through them
- same as with dimmable CFLs. All that is necessary is to make the
current control circuitry in the LED "bulbs" compatible with and making
use from the usual dimmers, similar story as with CFLs.

I was taught (in college) that once break-through voltage is
equaled, that's it, on or off. Now I have to learn WTF went wrong
in my imaginary circuit if that is true.

KRW is right that there is some difference in the voltage drop across
the junction as the current rises., It is not a big difference but it
is a difference.(1.79 - 1.96 in the ones I tested over a range of 3ma
to 15ma) It could just be heat doing it at the high end.

It's not heat. The I-V curve is an exponential, just like any other
(semiconductor) diode. Heat will flatten out the ideal I-V curve further but
that generally isn't seen until the device is operating outside of normal. The
effects of heat can be seen if you change current (and measure the voltage)
quickly.

Experiment: Take your diode and a resistor, connected in series with a
variable voltage source, as such.


+---------------+----------o +
| | |
| | .-. |
| I | | | R Vr
+ | | | |
| V '-' |
/+\ | |
V ( ) +----------o -
\-/ | +
| V - |
| - Vled
| | |
=== +----------o -
GND |
===
GND


Vary the voltage source and plot Vr and Vled in a spreadsheet. Calculate
(using the spreadsheet) I (=Vr/R) and then, again using the spreadsheet, graph
I (Y-axis) against Vled (X-axis) using the "scatter" option. This graph shows
the characteristic I-V curve of this diode and can be used to set the bias
resistors for any supply voltage (if the current is within the range of the
graph). Note that each diode will be somewhat different and diodes from each
batch (or "lot") can be significantly different. You might notice that LEDs
of the same part number and manufacturer may be "grouped" by brightness (and
even color). Two LEDs with the same specs may look entirely different if put
next to each other.

I did notice
in my flashlight tests that have no internal esistor that a very small
series resistance starts dropping the current very fast so they may be
using this "wall" of a heated junction to regulate the current,
similar to a nichrome wire.

The internal resistance of the battery is the ballast. Measure the unloaded
voltage (open-circuit or Voc, below) of the battery and the voltage and
current (this will be difficult) of the battery/LED combination. The internal
resistance of the battery can be calculated from (Voc-Vled)/I.

On Sun, 26 Dec 2010 22:20:45 -0600, G. Morgan wrote:

wrote:

On Sun, 26 Dec 2010 21:17:20 -0600, G. Morgan
wrote:

(Don Klipstein) wrote:

Brightness of LEDs is controlled by how much current flows through them
- same as with dimmable CFLs. All that is necessary is to make the
current control circuitry in the LED "bulbs" compatible with and making
use from the usual dimmers, similar story as with CFLs.

I was taught (in college) that once break-through voltage is
equaled, that's it, on or off. Now I have to learn WTF went wrong
in my imaginary circuit if that is true.

KRW is right that there is some difference in the voltage drop across
the junction as the current rises., It is not a big difference but it
is a difference.(1.79 - 1.96 in the ones I tested over a range of 3ma
to 15ma) It could just be heat doing it at the high end. I did notice
in my flashlight tests that have no internal esistor that a very small
series resistance starts dropping the current very fast so they may be
using this "wall" of a heated junction to regulate the current,
similar to a nichrome wire.

The only way to get an LED to work is put a resistor in series.
Are you sure the (bulb, lamp, LED) was not a 'package'? They sell
them both ways, people who want only the LED (specialized), and
people who just want it to work. The later is what I think is
causing this confusion.

The battery *is* the resistor.

On Mon, 27 Dec 2010 07:13:36 -0600, Jim Yanik wrote:

" wrote in
:

On Sun, 26 Dec 2010 16:02:42 -0500, wrote:

On Sun, 26 Dec 2010 12:41:26 -0600, "
wrote:

Probably parallel strings of LEDs.

*Series* strings. Parallel does nothing but cause more trouble. ;-)

OK the science comes fast around here
I took a flashlight apart.
It appears they use a 4.5v LED, 9 in parallel with NO resistor at all.
The internal resistance of 3 AAA cells seems to be the limiter

I've seen that too; a very poor design. There is nothing to
current-share across the LEDs. Counting on the internal resistance of
a battery is really ****-poor.

hey,they were FREE,including the batteries. ;-)
HF gives them away free with a coupon from their many ads.

HF buys their stuff from where? ;-)

of course,they don't use the batteries efficiently.

The problem that I have with it is counting on the internal resistance of the
battery. As long as the same *type* of battery is used there isn't a real
problem. If another type is used things can go very wrong.

On Mon, 27 Dec 2010 07:15:08 -0600, Jim Yanik wrote:

" wrote in
:

On Sun, 26 Dec 2010 16:02:42 -0500, wrote:

On Sun, 26 Dec 2010 12:41:26 -0600, "
wrote:

Probably parallel strings of LEDs.

*Series* strings. Parallel does nothing but cause more trouble. ;-)

OK the science comes fast around here
I took a flashlight apart.
It appears they use a 4.5v LED, 9 in parallel with NO resistor at all.
The internal resistance of 3 AAA cells seems to be the limiter

I've seen that too; a very poor design. There is nothing to
current-share across the LEDs. Counting on the internal resistance of
a battery is really ****-poor.

With just the batteries in there the lights are pulling about 244ma
(they are fairly new batteries)
This is hurt your eyes bright.
I put my 1k pot in there and even all the way off I am dropping .05v,
current around 211ma.

I assume you mean, "all the way *ON*", as in "zero" ohms (the wiper
resistance is about 1/4ohm).

don't forget the meter resistance,too.

Oh, certainly. Good catch.

On Mon, 27 Dec 2010 07:09:29 -0600, Jim Yanik wrote:

" wrote in
:

On Sun, 26 Dec 2010 12:02:15 -0600, Jim Yanik wrote:


Probably parallel strings of LEDs.

*Series* strings. Parallel does nothing but cause more trouble. ;-)


I meant several series strings -in parallel-.

curiously,some free Harbor Freight 9 LED flashlights I have have all 9
LED's in parallel,and no current limiting resistor,depending instead on the
internal resistance of the 3 AAA cells.

That's a current-sharing nightmare waiting to happen. I suppose the LEDs are
all from the same batch, so at least in theory, it works. ...well enough for
cheap Chinese junk, anyway.

Thinking about it a little, the temperature coefficients are in the right
direction so at least the thing isn't going to run away.

On Mon, 27 Dec 2010 16:54:10 +0000 (UTC), (Don Klipstein)
wrote:

In , zzzzzz wrote:
On Sun, 26 Dec 2010 23:56:01 +0000 (UTC), (Don
Klipstein) wrote:

In , zzzz wrote:
On Sun, 26 Dec 2010 21:31:57 +0000 (UTC), (Don
Klipstein) wrote:

One more thing: For outdoor or basement nightlighting or security
lighting, I strongly recommend that any white lights (LED or otherwise)
be of cooler color (more bluish, higher color temperature). This is
because night vision is significant in such dimmer lighting environments,
even if colors and sharp outlines are visible. A spectrum richer in
mid-green to mid-blue favors greater illumination in this case.

For indoor, basement, indoor security, and night-lights, I'd think you'd
want more of a red so you don't spoil your night vision. ...or maybe a
white photo-flash and cover *your* eyes, while the no-good gets blinded.
;-)

I've tried all sorts of things for seeing around with little light.
My experience says to make use of night vision. A cool white LED can
illuminate a room to extent that I can walk around and see everything,
using a couple to a few percent as much light as if I used red light.

That's interesting and a bit counterintuitive. I can see fine around the
bedroom, at night, with only the backlight of my XM radio but it's quite
bright. I guess it's not enough to trigger the iris but still make use of the
higher sensitivity wavelengths. OTOH, for astronomical viewing (and
submarines one uses red lights.

Oh yes, I do remember my stretch of time when I was into astronomy.

Red lights were used to see things other than stars, such as star maps,
so as to see in high resolution (from photopic vision) with light that
does not overload and reduce sensitivity of scotopic vision.

I would think the requirements of nightlights are usually different. I
don't see the need to be able to read a newspaper - only to recognize it,
to be able to read the name of the newspaper. There is also the fact
that I don't mind having my night vision attenuated a bit by using a light
that makes use of it for this purpose. I have some green and blue LEDs
that can illuminate a largish living room that well to me with maybe .1
milliamp (and full dark adaptation), though I would only count on low
current performance good enough to do that with .25 milliamp.

I still don't want to lose "night sight" when I stumble from one room into the
next, at night. The light doesn't alter my Braille ability, though. ;-)

On Sun, 26 Dec 2010 20:25:53 -0500, wrote:

On Sun, 26 Dec 2010 17:21:21 -0600, "
wrote:

You keep talking about this waste heat like we were dissipating
hundreds of watts. I only say rheostat to define a single ended pot.
If the ballast resistor is 1/2w or even 1/4w why would the pot need to
be any bigger?

You're not talking about illumination at these power levels.

I suppose that depends on what kind of illumination you are talking
about. If you mean replacing a couple hundred watts of incandescent, I
tend to agree, absent of more knowledge but if you are talking about
accent lighting, what you likely want to dim, I am not sure you need a
whole lot more than the equivalent of a few of these flashlights.

I thought you wanted task lighting under kitchen cabinets. That has to be
quite bright, even in a well lit room. A couple of watts isn't going to cut
it.

I don't know how a 120v bulb works but I can guess based on my
flashlight investigation.

Series strings of LEDs with a ballast.

These things are very bright at 26.6ma in this flashlight. If you had
about 25 of them in series (dropping ~112.5v) and a resistor 300-350
ohms you would be dropping around a quarter of a watt across it with a
3.1w total package. Putting a 1k pot in series with this is not going
to be that wasteful even if it does offend your engineering
sensibilities. You don't like the flashlight either but there are
millions of them out there working just fine.

I don't like them because some day someone is going to put the wrong battery
in the things.

I understand the engineering frame of mind but I also understand
simple is good.

Agreed, but too simple is not. ...primarily because people are. ;-)

The reality is the waste heat drops as the dimming starts.because that
"I2" thing is falling off very fast as the "R" goes up.

The *waste* heat may go *up* as dimming starts. The waste heat is V^2/R.

I am going to get one of these bulbs the next time I see one and we
will rewind the experiment at 120v. I think they are at the HD/Lowes.
My immediate interest is if they have some kind of voltage regulation.

They don't. Voltage regulation would serve little purpose.

My line voltage cruises in the 123-124 range. I bet they are very
bright if they are not regulated. Of course if it is regulated, the
pot won't really work until I get down to the regulated voltage but
that regulator is wasting power too.

Right.

If it has a switcher power supply in it, all bets are off. Nothing
will really dim it. I bet I can see a switcher on a scope. They are
not going to have that good a filter in them. CFL currents are really
ugly on a scope.

You should easily be able to see a switcher's signature. If you have a scope,
you can also see the effect of heating by driving the LEDs from an AC source.

This is a current transformer, looking at a CFL
http://gfretwell.com/electrical/CT%20fun/CFL%20wave.jpg

Yep, a few million of them will really screw with the power factor. ;-)
You'll see some oddities with LED lamps, too.

On Mon, 27 Dec 2010 07:17:59 -0600, Jim Yanik wrote:

" wrote in
:

On Sun, 26 Dec 2010 15:17:19 -0500, wrote:

On Sun, 26 Dec 2010 11:49:47 -0600, Jim Yanik
wrote:

LEDs can pop very fast when overdriven.(as the rheostat guy will
discover)

Since the rheostat will be in series with the proper "full load"
ballast resistor, overdriving is not an issue. Current is going to be
dropping as a square of the change in resistance and so will the heat.
As long as the rheostat is rated as high as the ballast resistor,
where is the possibility of a problem?

High power rheostats aren't all that common, or cheap, these days.

I suppose the open question is, how big is the resistor in a
commercial lamp?

I haven't seen a lamp with a rheostat is decades.

In my case it doesn't matter at all since I will be driving mine from
a wall wart. I am tempted to just take a cheap 4.5v LED flashlight
apart (a couple bucks at H.D) . That is probably cheaper than I can
buy 9 LEDS and for my purposes, it provides plenty of light. I just
want to spread them out a bit. I even have a 4.5v wall wart.

If you're powering this thing with a DC wall wart, simply PWM the
thing. For less than a buck or two in parts, you're all done, and you
can forget about the rheostat and waste heat.

his wallwart may burn them out,if it can supply more current than the LEDs
can handle;there's no limiting resistor.

Just gotta control the PWM better. ;-) A PWM current source is typically
used.

On Mon, 27 Dec 2010 15:40:13 -0500, wrote:

On Mon, 27 Dec 2010 13:36:14 -0600, "
wrote:

On Mon, 27 Dec 2010 07:15:08 -0600, Jim Yanik wrote:

" wrote in
:

On Sun, 26 Dec 2010 16:02:42 -0500, wrote:

On Sun, 26 Dec 2010 12:41:26 -0600, "
wrote:

Probably parallel strings of LEDs.

*Series* strings. Parallel does nothing but cause more trouble. ;-)

OK the science comes fast around here
I took a flashlight apart.
It appears they use a 4.5v LED, 9 in parallel with NO resistor at all.
The internal resistance of 3 AAA cells seems to be the limiter

I've seen that too; a very poor design. There is nothing to
current-share across the LEDs. Counting on the internal resistance of
a battery is really ****-poor.

With just the batteries in there the lights are pulling about 244ma
(they are fairly new batteries)
This is hurt your eyes bright.
I put my 1k pot in there and even all the way off I am dropping .05v,
current around 211ma.

I assume you mean, "all the way *ON*", as in "zero" ohms (the wiper
resistance is about 1/4ohm).

don't forget the meter resistance,too.

Oh, certainly. Good catch.

This is a Fluke 8060. I doubt that is a big deal and it was constant
between the LED with and without the pot. I suppose there is still
some drop tho.

Looking at the spec (for the 8062, looks to be the same as the 8060A), the
burden voltage on the 2A range (next down is 200mA and you said 211mA) is .9V
(.3V on the 200mA range). That's at FS, but I'd want to measure it to see how
much of that is resistive and how much is fixed. That'll certainly throw a
monkey wrench into your readings.

I have a hand full of Hi Intensity LEDs from those TV wonder lights
that I am going to play with tonight. I made a light bar out of some
wood scrap that matches my cabinet and I am going to see what happens.
I do believe, if you are dimming a LED array, low voltage may be your
friend, both from an application standpoint and a safety/UL listing
standpoint. Things are pretty lenient on the load side of a listed
class 2 power supply.

DC is your friend. PWM it. ;-)

I figure I will start out with a ballast resistor selected to apply
about 15ma "all in" and dim from there. From my experience with the
flashlight I think a 25 ohm pot will do a pretty good job and I have
one.

On Mon, 27 Dec 2010 15:48:03 -0500, wrote:

On Mon, 27 Dec 2010 13:58:41 -0600, "
wrote:

I am going to get one of these bulbs the next time I see one and we
will rewind the experiment at 120v. I think they are at the HD/Lowes.
My immediate interest is if they have some kind of voltage regulation.

They don't. Voltage regulation would serve little purpose.

If the voltage drop across the LEDs is somewhat fixed at a hundred and
sumpin

But there is your mistake. It is *NOT*.

and your ballast is picking up the slack, that slack can vary
quite a bit with the normal tolerance in power. A LED string that
works in the browned out north (108v or so) is going to be running
pretty hot here with my nominal 124v. That ballast needs to give you a
fairly reasonable current over a wide swing. I almost have to believe
they have real solid state current or voltage regulation, not just a
resistor.

Why? All they need to do is cover the maximum, so it doesn't burst into
flame.

If so, that is the problem with dimming them.

~:-/

" wrote in
:

On Mon, 27 Dec 2010 07:13:36 -0600, Jim Yanik
wrote:

" wrote in
m:

On Sun, 26 Dec 2010 16:02:42 -0500, wrote:

On Sun, 26 Dec 2010 12:41:26 -0600, "
wrote:

Probably parallel strings of LEDs.

*Series* strings. Parallel does nothing but cause more trouble.
;-)

OK the science comes fast around here
I took a flashlight apart.
It appears they use a 4.5v LED, 9 in parallel with NO resistor at
all. The internal resistance of 3 AAA cells seems to be the limiter

I've seen that too; a very poor design. There is nothing to
current-share across the LEDs. Counting on the internal resistance
of a battery is really ****-poor.

hey,they were FREE,including the batteries. ;-)
HF gives them away free with a coupon from their many ads.

HF buys their stuff from where? ;-)

Communist China. :-)

of course,they don't use the batteries efficiently.

The problem that I have with it is counting on the internal resistance
of the battery. As long as the same *type* of battery is used there
isn't a real problem. If another type is used things can go very
wrong.


they come with "heavy duty" AAA carbon-zincs,but I also tried alkalines
with them,and they were brighter with the carbon-zincs. they may be
UNDERdriven.
I still have two more coupons for free ones,and the local HF store is only
a short walk away!
Plus,I see the ads are still coming out with the coupons.

they're nice little flashlights for the "price"! B-)

--
Jim Yanik
jyanik
at
localnet
dot com

" wrote in
:

On Mon, 27 Dec 2010 07:17:59 -0600, Jim Yanik
wrote:

" wrote in
m:

On Sun, 26 Dec 2010 15:17:19 -0500, wrote:

On Sun, 26 Dec 2010 11:49:47 -0600, Jim Yanik
wrote:

LEDs can pop very fast when overdriven.(as the rheostat guy will
discover)

Since the rheostat will be in series with the proper "full load"
ballast resistor, overdriving is not an issue. Current is going to
be dropping as a square of the change in resistance and so will the
heat. As long as the rheostat is rated as high as the ballast
resistor, where is the possibility of a problem?

High power rheostats aren't all that common, or cheap, these days.

I suppose the open question is, how big is the resistor in a
commercial lamp?

I haven't seen a lamp with a rheostat is decades.

In my case it doesn't matter at all since I will be driving mine
from a wall wart. I am tempted to just take a cheap 4.5v LED
flashlight apart (a couple bucks at H.D) . That is probably cheaper
than I can buy 9 LEDS and for my purposes, it provides plenty of
light. I just want to spread them out a bit. I even have a 4.5v wall
wart.

If you're powering this thing with a DC wall wart, simply PWM the
thing. For less than a buck or two in parts, you're all done, and
you can forget about the rheostat and waste heat.

his wallwart may burn them out,if it can supply more current than the
LEDs can handle;there's no limiting resistor.

Just gotta control the PWM better. ;-) A PWM current source is
typically used.


Well,you KNOW this guy is not going to use a PWM circuit with his
wallwart,just a pot(rheostat).

--
Jim Yanik
jyanik
at
localnet
dot com

" wrote in
:

On Sun, 26 Dec 2010 20:25:53 -0500, wrote:

On Sun, 26 Dec 2010 17:21:21 -0600, "
wrote:

You keep talking about this waste heat like we were dissipating
hundreds of watts. I only say rheostat to define a single ended
pot. If the ballast resistor is 1/2w or even 1/4w why would the pot
need to be any bigger?

You're not talking about illumination at these power levels.

I suppose that depends on what kind of illumination you are talking
about. If you mean replacing a couple hundred watts of incandescent, I
tend to agree, absent of more knowledge but if you are talking about
accent lighting, what you likely want to dim, I am not sure you need a
whole lot more than the equivalent of a few of these flashlights.

I thought you wanted task lighting under kitchen cabinets. That has
to be quite bright, even in a well lit room. A couple of watts isn't
going to cut it.

the usual "bright white" LED found in these flashlights is a ~0.1W light.
~3.5 @20ma.

I don't know how a 120v bulb works but I can guess based on my
flashlight investigation.

Series strings of LEDs with a ballast.

These things are very bright at 26.6ma in this flashlight.

26ma seems a bit high.

If you had
about 25 of them in series (dropping ~112.5v) and a resistor 300-350
ohms you would be dropping around a quarter of a watt across it with a
3.1w total package. Putting a 1k pot in series with this is not going
to be that wasteful even if it does offend your engineering
sensibilities. You don't like the flashlight either but there are
millions of them out there working just fine.

don't forget that 120VAC rectifies out to ~170 VDC,not 120 VDC.
for that string and a 350 ohm resistor,your LEDs are not going to last more
than a millisecond.
BTW,the "bright white" T1-3/4 LEDs work out to ~3.5v forward voltage.

I don't like them because some day someone is going to put the wrong
battery in the things.

not gonna happen;only 3 AAA cells will fit,there's a plastic battery holder
inside the flashlight barrel.

--
Jim Yanik
jyanik
at
localnet
dot com

" wrote in
:

On Mon, 27 Dec 2010 15:48:03 -0500, wrote:

On Mon, 27 Dec 2010 13:58:41 -0600, "
wrote:

I am going to get one of these bulbs the next time I see one and we
will rewind the experiment at 120v. I think they are at the HD/Lowes.
My immediate interest is if they have some kind of voltage regulation.

They don't. Voltage regulation would serve little purpose.

If the voltage drop across the LEDs is somewhat fixed at a hundred and
sumpin

But there is your mistake. It is *NOT*.

and your ballast is picking up the slack, that slack can vary
quite a bit with the normal tolerance in power. A LED string that
works in the browned out north (108v or so) is going to be running
pretty hot here with my nominal 124v. That ballast needs to give you a
fairly reasonable current over a wide swing. I almost have to believe
they have real solid state current or voltage regulation, not just a
resistor.

Why? All they need to do is cover the maximum, so it doesn't burst into
flame.

If so, that is the problem with dimming them.

~:-/


120VAC is RMS voltage,not PEAK voltage.
multiply by 1.414 if you want to find the DC voltage after rectification.

--
Jim Yanik
jyanik
at
localnet
dot com

On Mon, 27 Dec 2010 16:52:33 -0600, Jim Yanik wrote:

" wrote in
:

On Sun, 26 Dec 2010 20:25:53 -0500, wrote:

On Sun, 26 Dec 2010 17:21:21 -0600, "
wrote:

You keep talking about this waste heat like we were dissipating
hundreds of watts. I only say rheostat to define a single ended
pot. If the ballast resistor is 1/2w or even 1/4w why would the pot
need to be any bigger?

You're not talking about illumination at these power levels.

I suppose that depends on what kind of illumination you are talking
about. If you mean replacing a couple hundred watts of incandescent, I
tend to agree, absent of more knowledge but if you are talking about
accent lighting, what you likely want to dim, I am not sure you need a
whole lot more than the equivalent of a few of these flashlights.

I thought you wanted task lighting under kitchen cabinets. That has
to be quite bright, even in a well lit room. A couple of watts isn't
going to cut it.

the usual "bright white" LED found in these flashlights is a ~0.1W light.
~3.5 @20ma.

I don't know how a 120v bulb works but I can guess based on my
flashlight investigation.

Series strings of LEDs with a ballast.

These things are very bright at 26.6ma in this flashlight.

26ma seems a bit high.

If you had
about 25 of them in series (dropping ~112.5v) and a resistor 300-350
ohms you would be dropping around a quarter of a watt across it with a
3.1w total package. Putting a 1k pot in series with this is not going
to be that wasteful even if it does offend your engineering
sensibilities. You don't like the flashlight either but there are
millions of them out there working just fine.

don't forget that 120VAC rectifies out to ~170 VDC,not 120 VDC.

Only with a capacitor filter. It'll still have a 170V peak but the RMS will
still be ~120V. The current waveform will be messed, though.

for that string and a 350 ohm resistor,your LEDs are not going to last more
than a millisecond.
BTW,the "bright white" T1-3/4 LEDs work out to ~3.5v forward voltage.

I don't like them because some day someone is going to put the wrong
battery in the things.

not gonna happen;only 3 AAA cells will fit,there's a plastic battery holder
inside the flashlight barrel.

In *your* freebie HF flashlight, perhaps. In the case of the HF flashlights,
the zinc cells may be the worst case. I don't see evidence that this is the
case in every flashlight out there.

On Mon, 27 Dec 2010 16:40:53 -0600, Jim Yanik wrote:

" wrote in
:

On Mon, 27 Dec 2010 07:17:59 -0600, Jim Yanik
wrote:

" wrote in
:

On Sun, 26 Dec 2010 15:17:19 -0500, wrote:

On Sun, 26 Dec 2010 11:49:47 -0600, Jim Yanik
wrote:

LEDs can pop very fast when overdriven.(as the rheostat guy will
discover)

Since the rheostat will be in series with the proper "full load"
ballast resistor, overdriving is not an issue. Current is going to
be dropping as a square of the change in resistance and so will the
heat. As long as the rheostat is rated as high as the ballast
resistor, where is the possibility of a problem?

High power rheostats aren't all that common, or cheap, these days.

I suppose the open question is, how big is the resistor in a
commercial lamp?

I haven't seen a lamp with a rheostat is decades.

In my case it doesn't matter at all since I will be driving mine
from a wall wart. I am tempted to just take a cheap 4.5v LED
flashlight apart (a couple bucks at H.D) . That is probably cheaper
than I can buy 9 LEDS and for my purposes, it provides plenty of
light. I just want to spread them out a bit. I even have a 4.5v wall
wart.

If you're powering this thing with a DC wall wart, simply PWM the
thing. For less than a buck or two in parts, you're all done, and
you can forget about the rheostat and waste heat.

his wallwart may burn them out,if it can supply more current than the
LEDs can handle;there's no limiting resistor.

Just gotta control the PWM better. ;-) A PWM current source is
typically used.


Well,you KNOW this guy is not going to use a PWM circuit with his
wallwart,just a pot(rheostat).

Well, he's not going to PWM the wall wart (voltage source), either.

In , zzzzz wrote:
On 12/27/2010 16:54:10 +0 UTC, (Don Klipstein) wrote:

In , zzz wrote:
On Sun, 26 Dec 2010 23:56:01 +0000 (UTC), (Don
Klipstein) wrote:

SNIP to here as part of editing for space that I did here

I've tried all sorts of things for seeing around with little light.
My experience says to make use of night vision. A cool white LED can
illuminate a room to extent that I can walk around and see everything,
using a couple to a few percent as much light as if I used red light.

That's interesting and a bit counterintuitive. I can see fine around the
bedroom, at night, with only the backlight of my XM radio but it's quite
bright. I guess it's not enough to trigger the iris but still make use
of the higher sensitivity wavelengths. OTOH, for astronomical viewing
(and submarines one uses red lights.

Oh yes, I do remember my stretch of time when I was into astronomy.

Red lights were used to see things other than stars, such as star maps,
so as to see in high resolution (from photopic vision) with light that
does not overload and reduce sensitivity of scotopic vision.

I would think the requirements of nightlights are usually different. I
don't see the need to be able to read a newspaper - only to recognize it,
to be able to read the name of the newspaper. There is also the fact
that I don't mind having my night vision attenuated a bit by using a light
that makes use of it for this purpose. I have some green and blue LEDs
that can illuminate a largish living room that well to me with maybe .1
milliamp (and full dark adaptation), though I would only count on low
current performance good enough to do that with .25 milliamp.

I still don't want to lose "night sight" when I stumble from one room
into the next, at night. The light doesn't alter my Braille ability,
though. ;-)

I'm thinking that illuminating a largish living room with one of my
favorite green or blue LEDs at .1-.25 mA will be low enough on blasting my
night vision for me to still have a majority of it, probably around/over
75% of it.

Then again, I can illuminate all rooms and the basement of a McMansion
that brightly with 50 milliwatts for the whole house.
(Not that I get a good ROI for doing so, in comparison to getting
commercially available LED nightlights using ~100 times as much power
and producing a few times more light.)
--
- Don Klipstein )

On Sun, 26 Dec 2010 22:20:45 -0600, G. Morgan
wrote:

wrote:

On Sun, 26 Dec 2010 21:17:20 -0600, G. Morgan
wrote:

(Don Klipstein) wrote:

Brightness of LEDs is controlled by how much current flows through them
- same as with dimmable CFLs. All that is necessary is to make the
current control circuitry in the LED "bulbs" compatible with and making
use from the usual dimmers, similar story as with CFLs.

I was taught (in college) that once break-through voltage is
equaled, that's it, on or off. Now I have to learn WTF went wrong
in my imaginary circuit if that is true.

KRW is right that there is some difference in the voltage drop across
the junction as the current rises., It is not a big difference but it
is a difference.(1.79 - 1.96 in the ones I tested over a range of 3ma
to 15ma) It could just be heat doing it at the high end. I did notice
in my flashlight tests that have no internal esistor that a very small
series resistance starts dropping the current very fast so they may be
using this "wall" of a heated junction to regulate the current,
similar to a nichrome wire.

The only way to get an LED to work is put a resistor in series.
Are you sure the (bulb, lamp, LED) was not a 'package'? They sell
them both ways, people who want only the LED (specialized), and
people who just want it to work. The later is what I think is
causing this confusion.
No, an LED will light very nicely with no resistor if the voltage is
close enough to the forward drop of the led. Excede that voltage by
very much and the current goes up real fast, very quickly exceding the
maximum power dissipation of the LED, and popping it.

If I set my lab supply to 15MA and connect a standard red LED I get
1.9 volts drop across it. I can stiffen that power supply so it can
supply 20 amps of power, and as long as I do not increase the voltage
above 1.9 volts, the current does not excede 15ma
Below 1.45 volts, the LED does not light at all, and it varies in
brightness quite linearly from 1.5 to 1.9 volts

With an 82 ohm resistor in series,changing the input voltage from 1.5
to 14, the voltage drop across the LED goes from 1.5 to 1.9 volts,
with the current reaching 15ma. (roughly.02 watts) while the poor
resistor is shedding 1.875 watts.

Without the resistor,25 ma of current produces a 1.91 volt drop,30ma
produces 1.98 volt drop,35ma is 2 volts, and going to 50 ma goes to
2.06

So doubling the current from 25ma to 50ma only raises the voltage drop
by .08 volts, which is roughly 4% on this 20ma rated device (I believe
that is the spec)

On Dec 26, 11:51*pm, wrote:
On Sun, 26 Dec 2010 20:27:58 -0800 (PST), JIMMIE



wrote:
On Dec 26, 2:54*am, wrote:
On Sat, 25 Dec 2010 22:36:45 -0600, wrote:
I like doing experiments like this and I will be back as soon as my
high intensity LEDs arrive because this is my plan. We will see.
I have no problem admitting when I am wrong but I want to see it.

Go for it. *I do this stuff all the time, though with indicators, not
for illumination. *

OK Here you go

These are garden variety indicator LEDs (what I had handy)
There is a 270 ohm in series with 4 LEDs and a 1k pot wired as a
rheostat.
With the pot set to 0 ohms get a tad over 15M/A and the LEDs are as
bright as you can expect from these, may even be overdriven. I al
dropping 4.11v over the 270 ohm resistor.
Turning the pot down toward 1k ohms dims the LEDs quite smoothly
At 1K ohms plus the 270 I get 3.7 MA or so and I am dropping 4.8 volts
across the resistors.http://gfretwell.com/electrical/LED%...experiment.jpg

I agree it is not exactly linear but I also do not understand how this
small variance makes any real world difference since most of the
voltage is still being dropped across the LED string. You certainly
would have a hard time seeing it on your electric bill.

You should see the PWM method. brightness is variable from next to
nothing to full bright. They also retain their color while white
lights turn yellow using your method.

Jimmie

I think most people find the color change to a softer color is part of
the reason they want to dim the light.
You usually dim accent lights or to turn task light to accent light.
Bear in mind in my house I have a bunch or rope lights and 15w sign
bulbs for our normal lighting and we use task lighting where we are
reading or doing some kind of work. That is why my under cabinet light
will probably be the 9 LEDs from a $2 flashlight and on a dimmer.
I just want enough light to mix a drink. ;-)
The light follows you wherever you go in the house but it is generally
fairly low level light. (rope light under toe kicks and overhead in
crown moldings) on motion sensors.
Outside most of my motion lighting is 15w sign bulbs but there are
lots of them. I hate that "Stallag 13" look you get with Par 38s.

The yellow lights didnt look good at all to me, of course this may
have something to do with the color of my counter top too. I have been
thinking of experimenting with combining different color LEDs in the
same cluster. Replacing one of the LEDs with a yellow one might not be
a bad idea. LEDs arent ideal for task lighting so why use them for
that. I used to have some light fixtures that had fluorescent, 60 watt
incandescent and night light type bulbs all in one fixture. I can see
where combining fluorescent and LED in an under-cabinet light would
have some advantages.