Hi Keith and Joel,

Thanks for the great links and concern over my health! I get this group in
digest form and have been off-line for a couple of days. Please excuse the
tardy response. 'No intent to keep anyone in suspense. I assumed everyone
knew about this LED and am pleasantly surprised that the info. seems to be
of interest.

This was a spur-of-the-moment project, slapped together late one night as a
"proof of concept." Since it actually works, I'm now forced to go back and
figure out what I did.

Towards that end I've created a quick-and-dirty website with photos and will
update as I get more time to work on the scope:

http://eldredspellflutes.com/LED_index.htm

I ended up with resistors and a 6-pole switch for brightness control (what
was in my parts bin that particular night). The necessary range is roughly
2.7 to 6 volts. You can calculate the resistance needed with Ohm's law, but
since the driver appears to be an active system, I just hooked it to a
resistance substitution box and dialed up what was needed. If anyone wants
the values, I'll gladly go back and measure them. I did try a variable
voltage regulator - thinking I could use it with a variety of sources - but
the initial voltage drop was enough to make four D-cells (the ultimate goal)
unworkable. It would be fine with a 12-volt supply. A rheostat ("pot" in
the vernacular) would be fine IF it can handle the maximum wattage. I have
several wire-wound types, but none were near the required range. A normal
pot from Radio Shack would be fine at the dimmest setting, but as you
increase brightness, the source of light will abruptly move from the LED to
the pot itself :-o

Since the LED is a diode, it will run off a regular 6-volt AC microscope
transformer, HOWEVER . . . transformers are inductors, which inherently
store and release energy. As Gordon pointed out, over-voltage is not good.
A lamp filament will stand some abuse, but even a short spike converts the
LED into a fast-acting fuse. You should add a diodes and a capacitor - - or
just get a 6-volt regulated DC power supply.

I did mention wanting to add a UV filter. Gordon's reassurance about the
Luxeon LED was a great relief, but there is always a fly in the oiintment
somewhere. Upon close examination, I do believe this LED is made by someone
else. I do not intend to use it seriously until I can either measure and/or
filter the output.

The AO Series 4 collector is frosted, so the beam pattern of the LED isn't
particularly important for this application. This is one of the few scopes
where the lamp is pointed head-on at the collector. THEREFORE, if someone
has a complete Series 4, it should be possible to either replace the
lamp-holder or possibly just make a socket adapter. If there's sufficient
interest, let me know and I'll do a small production run.

The heat-sink issue mentioned on one of Keith's links is of concern. I
used a brass mount and a large slug of aluminum which together have a lot of
themal inertia. Cooling fins could be added quickly, but I doubt if any of
that will make much of a difference. The LED and board are physically
isolated, so there's little possibility for conductive cooling. When I have
another $20 for research, I'll try removing the LED from the housing and
mounting it directly on a chunk of aluminum. That arrangement should also
allow adaptation to almost any microscope.

BTW - There is a great article on using the real Luxeon color LED's for
fluorescence microscopy here:

http://www.viewsfromscience.com/documents/webpages/led_fluorescence.html

Unfortunately, none of the wavelengths correspond to my filters, so I'm
still stuck with mercury arc :-(

All the best!

Eldred






Re: Digest Number 2559 - Maglite 3W LED
Posted by: "scitech200" scitech200@... scitech200
Fri Nov 10, 2006 5:50 am (PST)
"Eldred Spell" wrote:
> I just converted an AO Series 4 to a 3-watt LED. It's a Luxeon in >
a "Mag-Lite Upgrade" from Wal-Mart - $19 including the flashlight->
bulb shaped mount and drive circuit.

Thanks Eldred - a great find! I'm off to Walmart tomorrow...

I expect there will be a lot of interest in this LED assembly, so I
would like to recommend this review:
http://www.flashlightreviews.com/reviews/maglite_mag-led.htm

and for the nitty-gritty technical stuff:
http://candlepowerforums.com/vb/showthread.php?t=119665&highlight=mag-
led

Regards, Keith