Conducting Bench Top Material
Hmm. Has anyone built a strobe light using LEDs instead of a xenon
flash tube? I can see the appeal of building something that doesn't
need high voltage to fire or trigger the tube. Yes, you probably
couldn't get as much light as a big Xenon tube, but there are
applications where you don't need to illuminate a large area. (Recent
example of where I wished I had a stroboscope: looking at the balance
wheel of a pocket watch).
How high can you push the drive current of a LED if the pulse is short?
Of course you have to keep the average dissipation below what the device
is rated for, but there must be a peak current limit too.
Dave
On 30/01/2010 01:17, Robert Atkinson wrote:
Hi,I'm late to the thread (as usual), but have looked at these LED's in the past. It was for a biotech imaging application. There are two types, a red/green/blue cluster or a blue / near UV LED with a white phosphor. These phosphors seem to have a fairly continuous spectrum, at least compared to fluorescent lamps and HID lamps. What surprised me was the speed. We had a strobe application for which a xenon strobe was proposed. I tried LED's (our optics "expert" said even normal LED's would not be fast enough). I knew normal LED's are fast enough but was unsure about the phosphor types. To my surprise they where faster than the xenon tube! They were faster than my detector. This has has an impact on the mill illumination in that you can get strobe effects that could cause you to think the spindle was stationary when it was not. This is more of a problem in a noisy environment than a home shop with only one machine running.
Robert G8RPI.
I have some Philips LED halogen downlighter replacements. They are rated at 3W and produce a noticeable glow when "OFF". They are on a 2-way circuit and the stray capacitance of the wiring allows enough current for a faint glow.
Robert G8RPI.
--- On Sat, 30/1/10, Chuck Harris cfharris@erols.com wrote:
From: Chuck Harris cfharris@erols.com
Subject: Re: [time-nuts] White LED's
To: "Discussion of precise time and frequency measurement" time-nuts@febo.com
Date: Saturday, 30 January, 2010, 14:27
I bought some of the LED replacements for Edison bulb incandescents, and
they have an afterglow that lasts for several minutes. It is very much
dimmer than when they are turned on, but is there none the less.
-Chuck
Bruce Griffiths wrote:
The speed isn't terribly surprising since the "phosphor" used is actually a scintillator.
Unlike phosphors scintillators don't have long decay times so there is no afterglow like that from a phosphor.
The IKEA LED lamp output may not be significantly modulated if the wall wart constant current supply may have an output thats a little smoother than just rectified AC.
Bruce
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There are also large differences in rated lifetime; look at the fine
print on the package.
I've had some early Philips units that I used in a timer-driven lamp;
they were on for hours every day. The lamp lasted for years and years
and I eventually threw it out because it had gotten dim (the tube was
visibly blackened inside), but it was still working. It was rated for
10000 hours, and probably reached that before I junked it.
On the other hand, I've had some cheap Ikea lamps fail in ceiling lights
in little more than a year. The electronics self-destructed. Took a
close look at the package for a new one, and they are rated for only
2000 hours - which is easy to use up in a year in a room where the
lights are on 6 hours every evening.
Now, using CFLs of any type reduces electricity use compared to
incandescent, and that's worthwhile in many applications. But CFLs also
add a bunch of electronics parts to the waste stream when they are
thrown out - they're much worse than incandescents in that respect. So
when I use fluorescents, I prefer replaceable-tube units (where the
electronics in the ballast will last for decades, not be replaced every
couple of years). In places where I need a screw-in self-ballast type,
I look for the more expensive 10,000 hour types instead of the cheap
2000-hour ones.
And, as someone else pointed out, it doesn't make much sense to use CFLs
in applications where they are turned on and off a lot, since their life
will be much shorter than rated. (But LEDs should be fine for this,
once the price comes down a bunch).
Dave
On 30/01/2010 05:31, Didier Juges wrote:
Also they are very sensitive to heat, so do not use them in an enclosed
fixture.
I have been burned (figuratively) with these two gotchas, there may be more.
The one that lasts the longest in my house is the outside light at my back
door. It is turned on once a day around 6-7 PM and off in the morning, so
about 12 hours a day every day, and it lasts for years at that rate. Those
in the bathroom that get to be turned on and off several times a day for a
relatively short time don't do nearly as well.
Didier
Hi Dave,Yes I have. There was also a design in Nuts&Volts a while back. Generally if you keep the duty cycle low (<1:20) and pulses short (<20ms) you can push most LED's to about ten times their maximum continuous rated current without ill effect. Looking at the continuous and pulse ratings of IR LED's can give an idea of the "abuse" LED's can handle. Some small white LEDs do have pulse specifications, they are used as the flash in cell phone cameras. They make very good small strobes with much less "tail" than the $200 miniature Hamamatsu xenon tubes we were comparing them to.
Robert.G8RPI.
--- On Sat, 30/1/10, Dave Martindale dave.martindale@gmail.com wrote:
From: Dave Martindale dave.martindale@gmail.com
Subject: Re: [time-nuts] White LED's
To: "Discussion of precise time and frequency measurement" time-nuts@febo.com
Date: Saturday, 30 January, 2010, 19:12
Hmm. Has anyone built a strobe light using LEDs instead of a xenon flash tube? I can see the appeal of building something that doesn't need high voltage to fire or trigger the tube. Yes, you probably couldn't get as much light as a big Xenon tube, but there are applications where you don't need to illuminate a large area. (Recent example of where I wished I had a stroboscope: looking at the balance wheel of a pocket watch).
How high can you push the drive current of a LED if the pulse is short? Of course you have to keep the average dissipation below what the device is rated for, but there must be a peak current limit too.
Dave
On 30/01/2010 01:17, Robert Atkinson wrote:
Hi,I'm late to the thread (as usual), but have looked at these LED's in the past. It was for a biotech imaging application. There are two types, a red/green/blue cluster or a blue / near UV LED with a white phosphor. These phosphors seem to have a fairly continuous spectrum, at least compared to fluorescent lamps and HID lamps. What surprised me was the speed. We had a strobe application for which a xenon strobe was proposed. I tried LED's (our optics "expert" said even normal LED's would not be fast enough). I knew normal LED's are fast enough but was unsure about the phosphor types. To my surprise they where faster than the xenon tube! They were faster than my detector. This has has an impact on the mill illumination in that you can get strobe effects that could cause you to think the spindle was stationary when it was not. This is more of a problem in a noisy environment than a home shop with only one machine running. Robert G8RPI.
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Hi Dave:
LEDs are used on many cell phone cameras in just that way. The data
sheets for the LEDs have the pulse use specs.
At: http://www.sd36.bc.ca/sulhts/departments/elx/p/elec.html
scroll down to the "Boy Scout Motor" and notice a common LED held by two
wires that's being used as a strobe light.
Have Fun,
Brooke Clarke
http://www.PRC68.com
Dave Martindale wrote:
Hmm. Has anyone built a strobe light using LEDs instead of a xenon
flash tube? I can see the appeal of building something that doesn't
need high voltage to fire or trigger the tube. Yes, you probably
couldn't get as much light as a big Xenon tube, but there are
applications where you don't need to illuminate a large area. (Recent
example of where I wished I had a stroboscope: looking at the balance
wheel of a pocket watch).
How high can you push the drive current of a LED if the pulse is
short? Of course you have to keep the average dissipation below what
the device is rated for, but there must be a peak current limit too.
Dave
On 30/01/2010 01:17, Robert Atkinson wrote:
Hi,I'm late to the thread (as usual), but have looked at these LED's
in the past. It was for a biotech imaging application. There are two
types, a red/green/blue cluster or a blue / near UV LED with a white
phosphor. These phosphors seem to have a fairly continuous spectrum,
at least compared to fluorescent lamps and HID lamps. What surprised
me was the speed. We had a strobe application for which a xenon
strobe was proposed. I tried LED's (our optics "expert" said even
normal LED's would not be fast enough). I knew normal LED's are fast
enough but was unsure about the phosphor types. To my surprise they
where faster than the xenon tube! They were faster than my detector.
This has has an impact on the mill illumination in that you can get
strobe effects that could cause you to think the spindle was
stationary when it was not. This is more of a problem in a noisy
environment than a home shop with only one machine running. Robert
G8RPI.
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and follow the instructions there.
Chuck Harris wrote:
I bought some of the LED replacements for Edison bulb incandescents, and
they have an afterglow that lasts for several minutes. It is very much
dimmer than when they are turned on, but is there none the less.
-Chuck
Bruce Griffiths wrote:
The speed isn't terribly surprising since the "phosphor" used is
actually a scintillator.
Unlike phosphors scintillators don't have long decay times so there
is no afterglow like that from a phosphor.
The IKEA LED lamp output may not be significantly modulated if the
wall wart constant current supply may have an output thats a little
smoother than just rectified AC.
Bruce
Some white LEDs use phosphors, others use scintillators it varies from
manufacturer to manufacturer and part no to part no.
Bruce
I remember hearing about a law suit in an engineering law class I had to
take way back when. It seems a farmer had a long fence running under and
parallel to a high tension distribution line. He had hidden a copper line
in it and was harvesting enough power to operate most of his farm buildings.
This amounted to a measurable loss from the distribution line and the power
company found him out and sued. The court ruled he had to pay for power
used in the past and stop getting his power that way. Considering the
source I don't think this is an urban legend.
Regards.
Max. K 4 O D S.
Email: max@maxsmusicplace.com
Transistor site http://www.funwithtransistors.net
Vacuum tube site: http://www.funwithtubes.net
Music site: http://www.maxsmusicplace.com
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----- Original Message -----
From: "Chuck Harris" cfharris@erols.com
To: "Discussion of precise time and frequency measurement"
time-nuts@febo.com
Sent: Saturday, January 30, 2010 12:21 PM
Subject: Re: [time-nuts] White LED's
Dr. David Kirkby wrote:
I should have added, it carried on glowing for some time after I got
home too. At that point, I was well away from the train lines, though we
do have 11 kV overhead cables around 30m from the house. It eventually
stopped glowing so I assume it was the presence of the overhead train
lines which caused this.
When I was a kid, there was a main set of high tension power lines several
hundred yards from my house. I had friends that had garden sheds under
the
towers that were lit by fluorescent lamps collecting the stray fields. A
piece of wire on each end of the bulb enhanced the effect.
I knew of one guy that had a big coil of wire in the roof of his shed
and he could light a 100W incandescent bulb from the stray fields.
-Chuck Harris
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19:35:00
Chuck Harris wrote:
I have several rooms that are lit exclusively with CFL's, and I find
that for best life, I have to leave them on all the time. That is what
EPA has found too! CFL's may take less power for a given illumination,
but the owners leave them on far longer than incandescent, and the net
result is greater power consumption overall.
Here's an interesting bit of opposite experience. When I had a
restaurant, I had a walk-in freezer. I wanted to know when the
compressor was running so I wired a light socket across the compressor
contactor coil terminals and located it where I could see it from the
dining room where I sat when not busy.
I tried all sorts of light in that thing. Long life, rough duty, pilot
light, none of them could stand the 2-3 times an hour cycling. Then I
installed a little 7 watt organ pipe CFL. It lasted over 5 years and
was still going strong when I closed the restaurant.
Add that to the mandatory drop of mercury in each, and I really can't
see how they can sell them at all.
Now Chuck, don't go getting all chemophobic on us now!
I got two for "free" from my power company (They hid the charge on my
bill, until the courts made them reverse it...) and included with the
CFL's was an elaborate procedure for cleaning up a broken CFL. It involved
opening all of the windows, and leaving the room for a couple of hours,
and then, with a gloved hand putting the pieces on newspaper, and folding
the newspaper up and putting it in a 1 gallon zip lock baggie. To clean up
the broken bits, you are supposed to vacuum the area with a fresh vacuum
cleaner bag, and then put the vacuum cleaner bag in a ziplock baggie, and
take the remains off to the hazardous waste disposal facility.
That's embarrassing to read, it's so stupid. Like some meaningless
worship ceremony to mother Gaia or something.
Geez, there's less than 10 milligrams of merc in a "100 watt" CFL. That
is a harmless amount, especially considering that elemental mercury is
fairly harmless.
What'll they come up with next, HAZMAT team if you spill some paint thinner?
John
--
John DeArmond
Tellico Plains, Occupied TN
http://www.neon-john.com <-- email from here
http://www.johndearmond.com <-- Best damned Blog on the net
PGP key: wwwkeys.pgp.net: BCB68D77
NeonJohn wrote:
Chuck Harris wrote:
I have several rooms that are lit exclusively with CFL's, and I find
that for best life, I have to leave them on all the time. That is what
EPA has found too! CFL's may take less power for a given illumination,
but the owners leave them on far longer than incandescent, and the net
result is greater power consumption overall.
Here's an interesting bit of opposite experience. When I had a
restaurant, I had a walk-in freezer. I wanted to know when the
compressor was running so I wired a light socket across the compressor
contactor coil terminals and located it where I could see it from the
dining room where I sat when not busy.
I tried all sorts of light in that thing. Long life, rough duty, pilot
light, none of them could stand the 2-3 times an hour cycling. Then I
installed a little 7 watt organ pipe CFL. It lasted over 5 years and
was still going strong when I closed the restaurant.
Add that to the mandatory drop of mercury in each, and I really can't
see how they can sell them at all.
Now Chuck, don't go getting all chemophobic on us now!
I got two for "free" from my power company (They hid the charge on my
bill, until the courts made them reverse it...) and included with the
CFL's was an elaborate procedure for cleaning up a broken CFL. It involved
opening all of the windows, and leaving the room for a couple of hours,
and then, with a gloved hand putting the pieces on newspaper, and folding
the newspaper up and putting it in a 1 gallon zip lock baggie. To clean up
the broken bits, you are supposed to vacuum the area with a fresh vacuum
cleaner bag, and then put the vacuum cleaner bag in a ziplock baggie, and
take the remains off to the hazardous waste disposal facility.
That's embarrassing to read, it's so stupid. Like some meaningless
worship ceremony to mother Gaia or something.
Geez, there's less than 10 milligrams of merc in a "100 watt" CFL. That
is a harmless amount, especially considering that elemental mercury is
fairly harmless.
What'll they come up with next, HAZMAT team if you spill some paint thinner?
John
If the intention is to cleanup the mercury rather than just the glass
and relatively non toxic phosphor then the cleanup procedure is contrary
to the method outlined in:
http://www.p2pays.org/ref/15/14605.htm
If one is paranoid about mercury spills sprinkling the debris with
flowers of sulphur is a good idea especially if one intends to
repeatedly break CFLs in the same location.
Bruce
Oh I am certain that they can measure the losses, especially today.
I disagree that harvesting the fields from a hundred feet away is
theft, though. Especially if it is on your own property.
The easements on my property give the power companies the right
to come onto the property and maintain the lines, but they say
nothing about giving them the right to immerse my property in
high flux AC fields. They were written in a less technical era,
but they are still in force.
-Chuck Harris
Max Robinson wrote:
I remember hearing about a law suit in an engineering law class I had to
take way back when. It seems a farmer had a long fence running under
and parallel to a high tension distribution line. He had hidden a
copper line in it and was harvesting enough power to operate most of his
farm buildings. This amounted to a measurable loss from the distribution
line and the power company found him out and sued. The court ruled he
had to pay for power used in the past and stop getting his power that
way. Considering the source I don't think this is an urban legend.
Regards.
Max. K 4 O D S.