A couple of months ago I had an idea for a very compact but efficient
pocket flashlight. The idea was to use an offset-fed parabolic
reflector (like satellite TV) rather than the traditional flashlight
design. Computer models indicated it would work well. Then I got
sidetracked on other things.

I've revisited that with a quick 'n dirty experiment. It seems to
work on the bench as well as in the 'puter.

More at
http://users.goldengate.net/~dforeman/tinylight/

In article ,
Don Foreman wrote:

A couple of months ago I had an idea for a very compact but efficient
pocket flashlight. The idea was to use an offset-fed parabolic
reflector (like satellite TV) rather than the traditional flashlight
design. Computer models indicated it would work well. Then I got
sidetracked on other things.

I've revisited that with a quick 'n dirty experiment. It seems to
work on the bench as well as in the 'puter.

More at
http://users.goldengate.net/~dforeman/tinylight/

IIRC the military uses some LED flashlights with the LED mounted
'backwards' into a reflector because the beam is so much tighted so it
gets less backscatter in a dusty environment.

--
Free men own guns, slaves don't
www.geocities.com/CapitolHill/5357/

Very interesting, Don. Thanks for sharing.

Bob Swinney
"Nick Hull" wrote in message
...
In article ,
Don Foreman wrote:

A couple of months ago I had an idea for a very compact but efficient
pocket flashlight. The idea was to use an offset-fed parabolic
reflector (like satellite TV) rather than the traditional flashlight
design. Computer models indicated it would work well. Then I got
sidetracked on other things.

I've revisited that with a quick 'n dirty experiment. It seems to
work on the bench as well as in the 'puter.

More at
http://users.goldengate.net/~dforeman/tinylight/

IIRC the military uses some LED flashlights with the LED mounted
'backwards' into a reflector because the beam is so much tighted so it
gets less backscatter in a dusty environment.

--
Free men own guns, slaves don't
www.geocities.com/CapitolHill/5357/

On Thu, 03 Mar 2005 05:49:56 -0500, Nick Hull
wrote:

IIRC the military uses some LED flashlights with the LED mounted
'backwards' into a reflector because the beam is so much tighted so it
gets less backscatter in a dusty environment.

That might be the Pelican Recoil.
http://www.pelicanaustralia.com/ledlites.htm

Similar idea, but this requires a fairly large reflector so the 3/8"
dia body of the LED and its support structure don't present
significant obscuration.

I believe Ian Stirling is/was contemplating this configuration using a
sapphire lens as both support and heatsink.

Perhaps I'm missing something, but aren't you going to lose a lot of
optical efficiency with an offset feed unless you perform a somewhat
difficult change in the shape of the reflector to compensate for
off-axis illumination?

Since you have a computer, run a simple ray-tracing program and see
what the results are.


Harry C.

On 3 Mar 2005 14:10:19 -0800, wrote:

Perhaps I'm missing something, but aren't you going to lose a lot of
optical efficiency with an offset feed unless you perform a somewhat
difficult change in the shape of the reflector to compensate for
off-axis illumination?

No. Perhaps "offset feed" was misleading. "Assymetrical feed"
might have been better terminology. The light source is still at the
focal point of a paraboloid. Since the Luxeon is not
omnidirectional (as a lightbulb is), I'm simply orienting it to
maximize the amount of its light that hits the reflector rather than
going forward without hitting the reflector, and eliminating unused
portions of what would otherwise be a full paraboloid to get a low
profile.

Satellite TV antennae work the same way; the dishes are sections of a
paraboloid with the pickup head positioned so it doesn't obscure the
dish's "view".

Since you have a computer, run a simple ray-tracing program and see
what the results are.

Did that with MathCAD, got an intensity plot. The real-life spot on
the wall looks very similar to the simulation results.

Don Foreman wrote:
On Thu, 03 Mar 2005 05:49:56 -0500, Nick Hull
wrote:

IIRC the military uses some LED flashlights with the LED mounted
'backwards' into a reflector because the beam is so much tighted so it
gets less backscatter in a dusty environment.

That might be the Pelican Recoil.
http://www.pelicanaustralia.com/ledlites.htm

Similar idea, but this requires a fairly large reflector so the 3/8"
dia body of the LED and its support structure don't present
significant obscuration.

I believe Ian Stirling is/was contemplating this configuration using a
sapphire lens as both support and heatsink.

I am, I'm wondering at the moment if extracted dies from luxeon stars
is indeed the best way.

In the USA the first version of this light was the Stealthlite 2020 or something like that. It had a great beam that was almost square like the die of the LED itself. Scatter was almost nothing at all. The only flahslight I have with a beam nearly as tight is a Maxabeam.

The one I had had a screw to operate switch and was total garbage. They changed the materials used, but it was still poor. It was hard to turn on and off, or would turn on an off itself. There was never a clear separation between on and off either.

Pelican needs to come up with a better switch system. Toggles that don't lock on or off without a peg that breaks off is stupid.

Don Foreman wrote:
On Thu, 03 Mar 2005 05:49:56 -0500, Nick Hull
wrote:

IIRC the military uses some LED flashlights with the LED mounted
'backwards' into a reflector because the beam is so much tighted so it
gets less backscatter in a dusty environment.

That might be the Pelican Recoil.
http://www.pelicanaustralia.com/ledlites.htm

Similar idea, but this requires a fairly large reflector so the 3/8"
dia body of the LED and its support structure don't present
significant obscuration.

I believe Ian Stirling is/was contemplating this configuration using a
sapphire lens as both support and heatsink.

On 03 Mar 2005 23:37:13 GMT, Ian Stirling
wrote:

Don Foreman wrote:
On Thu, 03 Mar 2005 05:49:56 -0500, Nick Hull
wrote:

IIRC the military uses some LED flashlights with the LED mounted
'backwards' into a reflector because the beam is so much tighted so it
gets less backscatter in a dusty environment.

That might be the Pelican Recoil.
http://www.pelicanaustralia.com/ledlites.htm

Similar idea, but this requires a fairly large reflector so the 3/8"
dia body of the LED and its support structure don't present
significant obscuration.

I believe Ian Stirling is/was contemplating this configuration using a
sapphire lens as both support and heatsink.

I am, I'm wondering at the moment if extracted dies from luxeon stars
is indeed the best way.

Keep us posted, Ian! I use emitters rather than Stars, but
extracting the die would be well beyond my ability. I figure the
die is about 1 mm square while the emitter body is about 8 mm dia,
so you'd gain a little if you could do that. How much you'd gain
would depend on the reflector diameter.

Streamlight gets good results from batwing Luxeons in their very deep
short-focus reflectors. A batwing might be a good choice for a retro.

On Thu, 3 Mar 2005 23:58:39 +0000 (UTC), Crow Leader
wrote:

In the USA the first version of this light was the Stealthlite 2020 or something like that. It had a great beam that was almost square like the die of the LED itself. Scatter was almost nothing at all. The only flahslight I have with a beam nearly as tight is a Maxabeam.

The one I had had a screw to operate switch and was total garbage. They changed the materials used, but it was still poor. It was hard to turn on and off, or would turn on an off itself. There was never a clear separation between on and off either.

Pelican needs to come up with a better switch system. Toggles that don't lock on or off without a peg that breaks off is stupid.

Good small switches are hard to find unless you're buying in
production qty. I'm using magnetic reed switches. They're very
small, very reliable and hermetically sealed.

I think the assymetrically-fed (was "offset fed") paraboloid would
match the retro's beam tightness by simply blacking out the portion of
the Luxeon that can "see" directly out the reflector's aperture so
that *all* light is collimated. The loss that would produce is
probably less than the blockage presented by the emitter and support
structure in a retro design.

A little "spill" is generally not a bad thing in a flashlight. Don't
need or want much, just enough to see one's feet and immediate (arm's
length) surroundings and direct the rest where it's needed at greater
distance. A totally contained beam is only necessary if one is
concerned about backscatter in fog or very dusty condx. Tactical
users may also be concerned about ability of a distant off-axis
observer to localize the light -- and therefore it's user. (Think
target) In fog, rain, snow, dust, buggy or even humid condx the
beam will draw a line to the user anyway so the only real advantage is
freedom from being blinded by backscatter.

That form factor looks like it would work well attached to a headband.

--
Regards,
Carl Ijames carl.ijames at verizon.net

On Fri, 04 Mar 2005 02:41:19 GMT, the inscrutable "Carl Ijames"
spake:

That form factor looks like it would work well attached to a headband.

But with the battery on the back of the band, balancing the weight,
perhaps?


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Don Foreman wrote:
On Thu, 3 Mar 2005 23:58:39 +0000 (UTC), Crow Leader
wrote:

In the USA the first version of this light was the Stealthlite 2020 or something like that. It had a great beam that was almost square like the die of the LED itself. Scatter was almost nothing at all. The only flahslight I have with a beam nearly as tight is a Maxabeam.

The one I had had a screw to operate switch and was total garbage. They changed the materials used, but it was still poor. It was hard to turn on and off, or would turn on an off itself. There was never a clear separation between on and off either.

Pelican needs to come up with a better switch system. Toggles that don't lock on or off without a peg that breaks off is stupid.

Good small switches are hard to find unless you're buying in
production qty. I'm using magnetic reed switches. They're very
small, very reliable and hermetically sealed.

They make enough flashlights to tool up to make all those plastic parts. I like their toggle switch except for the fact you cannot lock it on or off without the peg. They should add an internal spring so it snaps on or off, like a normal rocker switch. Their service has been awful in the past year or so, so I'm off to new vendors now.




I think the assymetrically-fed (was "offset fed") paraboloid would
match the retro's beam tightness by simply blacking out the portion of
the Luxeon that can "see" directly out the reflector's aperture so
that *all* light is collimated. The loss that would produce is
probably less than the blockage presented by the emitter and support
structure in a retro design.

A little "spill" is generally not a bad thing in a flashlight. Don't
need or want much, just enough to see one's feet and immediate (arm's
length) surroundings and direct the rest where it's needed at greater
distance. A totally contained beam is only necessary if one is
concerned about backscatter in fog or very dusty condx. Tactical
users may also be concerned about ability of a distant off-axis
observer to localize the light -- and therefore it's user. (Think
target) In fog, rain, snow, dust, buggy or even humid condx the
beam will draw a line to the user anyway so the only real advantage is
freedom from being blinded by backscatter.

Don Foreman wrote:
On 03 Mar 2005 23:37:13 GMT, Ian Stirling
wrote:

Don Foreman wrote:
On Thu, 03 Mar 2005 05:49:56 -0500, Nick Hull
wrote:

IIRC the military uses some LED flashlights with the LED mounted
'backwards' into a reflector because the beam is so much tighted so it
gets less backscatter in a dusty environment.

That might be the Pelican Recoil.
http://www.pelicanaustralia.com/ledlites.htm

Similar idea, but this requires a fairly large reflector so the 3/8"
dia body of the LED and its support structure don't present
significant obscuration.

I believe Ian Stirling is/was contemplating this configuration using a
sapphire lens as both support and heatsink.

I am, I'm wondering at the moment if extracted dies from luxeon stars
is indeed the best way.

Keep us posted, Ian! I use emitters rather than Stars, but
extracting the die would be well beyond my ability. I figure the
die is about 1 mm square while the emitter body is about 8 mm dia,
so you'd gain a little if you could do that. How much you'd gain
would depend on the reflector diameter.

I'd like the total diameter of the light to be about 17mm or so, with a 14mm
or so clear apature.
8mm is really annoying in this case.
However, getting it to 5 is pretty easy.
I'm also investigating other ways.