Must an LED be flat? Why not shape like incan bulb?

An LED which was a curved surface could be shaped to optimize the beam & be focusable like an incan bulb with nearly 360 degree emission pattern.

Failing that, why are there no multiple LEDs on the surface of a hemisphere, or a section of a dodecahedron etc? They are doing this with household bulds by arranging several COBs inside the usual Edison bulb shape.

How hard would it be to install 5 LEDs on five faces of a cube & mount that in a Maglite or such with a big deep reflector to create a pencil beam?

You might even omit the forward LED and shape a TIR to bounce everything in a narrow beam.

lumen aeternum said:

An LED which was a curved surface could be shaped to optimize the beam & be focusable like an incan bulb with nearly 360 degree emission pattern.

Failing that, why are there no multiple LEDs on the surface of a hemisphere, or a section of a dodecahedron etc? They are doing this with household bulds by arranging several COBs inside the usual Edison bulb shape.

How hard would it be to install 5 LEDs on five faces of a cube & mount that in a Maglite or such with a big deep reflector to create a pencil beam?

You might even omit the forward LED and shape a TIR to bounce everything in a narrow beam.

Click to expand...

If you are trying to mimic the filament of an incan bulb using LED technology the problem is simple in that LEDs need decent heatsinking or they burn out and the best way to heatsink LEDs is to make them flat and use metal out one side. If you want an LED that isn't as bright you could probably do what you are thinking but ramp up the lumens and you have to increase the mass of the heatsink and make an effective path to the LED. Incan bulbs don't need heatsinking at all so the heat in a tiny area (the bulb filament) can be made small enough to sit in a parabolic reflector and focus.

Yes, to be flat is for heatsink. The larger the flat LED is, the faster it can dissipate heat.

Also, it is probably cheaper and easier to produce flat wafers and maintain proper chromacity.

I would imagine you would not be able to get LEDs thin enough to replicate an incandescent filament. Going with the light bulb approach, I think that would cause beam defects and by having more emitters would result in a higher surface area of light resulting in lower surface brightness, which defeats the whole purpose.

You could make a liquid cooled led assembly out on the top of a little pipe... or use a heat pipe, but I don't think they transfer much heat until there's enough heat built up yup power the steam - condensation -wicking cycle, so that might not work as well at the lower temp end as one might hope.
I'll bet either one would be a little pricy.

As the OP is kind of getting, the problem is size of the emitter. For lights that use a reflector, the ideal shape is parabolic. The ideal parabola works with a point light source at the primary focus. Incandescent bulbs work well because the filament is usually small enough to come close to a point source, and it can be placed within the mount so that the focus is in the middle of the filament. For those of you familiar with Maglites or zoomy LED lights, that is why one can see an image of the filament or LED when totally zoomed in. If one were to take one of the older 5mm LEDs like the ones used in the original Photon lights, the actual emitter is really very small, and works about as well as an incandescent bulb as far as approximating a point source. Any LED that is expected to produce more light than one of those is going to be larger, and therefore less like a point source. It is the light coming from the emitter, whether it is incandescent or LED, that is not at the focal point that causes most of the spill light seen. [A secondary source of spill is a shallow reflector that allows more rays to be emitted without being reflected and directed forward.] For a given reflector width and depth, a larger emitting area will always produce more spill than a smaller one.

I think one issue is that a true point source tends to emit light equally in a 360 degree output (or sphere) while LEDs tend to emit light unequally in a 180 degree output (half sphere) but more like a cone output fading to half sphere. This type of output is why deep and narrow reflectors are used for LEDs and optics work well as the light from perhaps 135 degrees to 180 degrees is a smaller portion of light such that losing that amount doesn't greatly affect the output overall of a flashlight. So regardless to how small the actual LED is made until is made to emit more evenly to about 270 degrees a parabolic reflector is not the ideal choice for a flashlight beam as it doesn't focus optimally on the greater output of LEDs and wastes a lot of reflector real estate on areas of output that either there is no light from 180-270 degrees or so, and also even areas from about 135-180 degrees and not addressing the 90-135 degree range which has the most intensity considerably more.

A lot of the light emitted from an LED is "wasted" because its not going in the desired direction & cannot be reflected into a useful direction.

So a curved surface LED could emit less light (so less heat) but all in a useful direction.

How about making the LED on the inside surface of a parabola? From the focal point to a couple of mm. Then the rest of the parabola is reflective as usual.

Silver is pretty cheap and a great conductor of heat.

lumen aeternum said:

A lot of the light emitted from an LED is "wasted" because its not going in the desired direction & cannot be reflected into a useful direction.

So a curved surface LED could emit less light (so less heat) but all in a useful direction.

How about making the LED on the inside surface of a parabola? From the focal point to a couple of mm. Then the rest of the parabola is reflective as usual.

Silver is pretty cheap and a great conductor of heat.

Click to expand...

I disagree about wasted light in LED flashlights as I've had LED lights with no spill at all and found them not useful.
making the LED on the parabola itself won't work because the focus point is NOT on the parabola at all but "in space" a distance from the surface of the parabola. Unless you want a wimpy LED output or spend a lot on silver to heatsink it I don't think you want to use silver for a heatsink I think copper is actually a better heat conductor than silver.

There used to be some lights that used a side emmiting LED that I think were supposed to give better throw. I don't know if they actually did that though as I never owned one and they obviously didn't catch on. Some of the side emitter LEDs used 2 dies firing in opposite directions and others used an optic.

Pelican on the other hand has come up with a different approach with their recoil series. They basically mount the LED facing the reflector, much like a satelite dish. This created a very narrow, spilless beam.

defloyd77 said:

Pelican on the other hand has come up with a different approach with their recoil series. They basically mount the LED facing the reflector, much like a satelite dish. This created a very narrow, spilless beam.

Click to expand...

Is that called Reflector Facing Technology (RFT)? hope I didn't make that up, but there was a thread recently discussing this sort of flashlight with inward reflector facing LED... it has a name, and there are many flashlights that utilize this tech. I seriously doubt this is originally Pelican's innovation, nor that they were first to bring such flashlights to market. Help me CPF, what is this called?

"the focus point is NOT on the parabola at all but "in space" a distance from the surface of the parabola"

Yes, I suggest that the portion from that point back, be an LED surface.

Pelican light models are not identified as being recoil; from comments the 2410 is a recoil but its under 200 Lumens. I think Pelican is aimed at firemen who need a narrow beam across a room. Not hunters at 100 yards.

Derelight (curiously spelled dereelight by its US distributor...) and ArmyTech seem to have some "pencil" beams but I can't prove it by specs or beamshots.

night.hoodie said:

Is that called Reflector Facing Technology (RFT)? hope I didn't make that up, but there was a thread recently discussing this sort of flashlight with inward reflector facing LED... it has a name, and there are many flashlights that utilize this tech. I seriously doubt this is originally Pelican's innovation, nor that they were first to bring such flashlights to market. Help me CPF, what is this called?

Click to expand...

I don't know who originally came out with the application of this in flashlights, but Pelican is probably the best known.

EDIT: All I know is Pelican does have a patent for this and these lights have been around longer than I have been on here. I've done a little Googling and most of the stuff I saw regarding RFT is relatively new and more for automotive applications.

lumen aeternum said:

"the focus point is NOT on the parabola at all but "in space" a distance from the surface of the parabola"

Yes, I suggest that the portion from that point back, be an LED surface.

Pelican light models are not identified as being recoil; from comments the 2410 is a recoil but its under 200 Lumens. I think Pelican is aimed at firemen who need a narrow beam across a room. Not hunters at 100 yards.

Derelight (curiously spelled dereelight by its US distributor...) and ArmyTech seem to have some "pencil" beams but I can't prove it by specs or beamshots.

Click to expand...

My point is there are many ways to look at what the OP is proposing and what the Pelican lights do is send virtually all of an emitter's light into the reflector to be focused into a throwy beam and they do it preexisting LEDs.

defloyd77 said:

There used to be some lights that used a side emmiting LED that I think were supposed to give better throw. I don't know if they actually did that though as I never owned one and they obviously didn't catch on. Some of the side emitter LEDs used 2 dies firing in opposite directions and others used an optic.

Pelican on the other hand has come up with a different approach with their recoil series. They basically mount the LED facing the reflector, much like a satelite dish. This created a very narrow, spilless beam.

Click to expand...

I remember the side emitting LEDs.... luxeons and I think it was an optic that converted them to side emitting regardless of it all they never made upgraded versions of these LEDs.

As for the recoil or whatever backwards firing LEDs I can see problems with them in modern high power lights in that if you want a lot of lumens you basically don't have enough heatsinking for the LED as normal lights use a larger slug and/or the body of the light to wick away heat. I seem to recall long ago incan lights using similar beam technology maybe some halogen driving or fog lights.

Lynx_Arc said:

I remember the side emitting LEDs.... luxeons and I think it was an optic that converted them to side emitting regardless of it all they never made upgraded versions of these LEDs.

As for the recoil or whatever backwards firing LEDs I can see problems with them in modern high power lights in that if you want a lot of lumens you basically don't have enough heatsinking for the LED as normal lights use a larger slug and/or the body of the light to wick away heat. I seem to recall long ago incan lights using similar beam technology maybe some halogen driving or fog lights.

Click to expand...

Luxeons did and still do make ones that use an optic, but I remember seeing one in a light on one of the old flashlight review sites that used 2 dies pointing sideways. I'm racking my brain trying to think of the review site.

As for recoil lights, the Pelicans have a problem because they are mounted on plastic, I would imagine if you could make that part aluminum, that could allow for better heat dissipation. The used to have a dual Luxeon V (I'm pretty sure) spotlight that had a little metal nub exposed through the plastic on the front to help with heat. If that could work with those 2 power hungry heaters, I think a more modern LED could work with an all aluminum mount.

night.hoodie said:

Is that called Reflector Facing Technology (RFT)? hope I didn't make that up, but there was a thread recently discussing this sort of flashlight with inward reflector facing LED... it has a name, and there are many flashlights that utilize this tech. I seriously doubt this is originally Pelican's innovation, nor that they were first to bring such flashlights to market. Help me CPF, what is this called?

Click to expand...

I can see where that would for all intents and purposes pretty much eliminate spill. Spill comes from two sources. First, there are the direct rays from the emitter that are never reflected but go directly outward. This is the type of spill that is controlled by using a narrow, deep reflector. Then there is the spill that comes from rays that have been reflected, but since they are not coming from the focus, are not reflected so that they are parallel with the main axis of the reflector. After one or more reflections they too will exit the reflector off-axis, so to speak, and thus illuminate the area around the main beam that is coming out on axis.

A rear firing emitter would totally eliminate the first source of spill, as there would be no direct, unreflected rays from the emitter leaving the light off axis. How much of the second source of spill would remain would be affected by the reflector design.

defloyd77 said:

Luxeons did and still do make ones that use an optic, but I remember seeing one in a light on one of the old flashlight review sites that used 2 dies pointing sideways. I'm racking my brain trying to think of the review site.

As for recoil lights, the Pelicans have a problem because they are mounted on plastic, I would imagine if you could make that part aluminum, that could allow for better heat dissipation. The used to have a dual Luxeon V (I'm pretty sure) spotlight that had a little metal nub exposed through the plastic on the front to help with heat. If that could work with those 2 power hungry heaters, I think a more modern LED could work with an all aluminum mount.

Click to expand...

Today's LEDs can withstand higher temperatures and output higher amounts of heat such that you need even larger heatsinking than older luxeons could handle so either you have to throttle back LED power or it would make for a rather deep reflector to accomodate a rather long cylindrical heat sink on the back of the LED.

Timothybil said:

I can see where that would for all intents and purposes pretty much eliminate spill. Spill comes from two sources. First, there are the direct rays from the emitter that are never reflected but go directly outward. This is the type of spill that is controlled by using a narrow, deep reflector. Then there is the spill that comes from rays that have been reflected, but since they are not coming from the focus, are not reflected so that they are parallel with the main axis of the reflector. After one or more reflections they too will exit the reflector off-axis, so to speak, and thus illuminate the area around the main beam that is coming out on axis.

A rear firing emitter would totally eliminate the first source of spill, as there would be no direct, unreflected rays from the emitter leaving the light off axis. How much of the second source of spill would remain would be affected by the reflector design.

Click to expand...

You would need a very small emitter and a large reflector in order to eliminate light escaping that isn't properly refocused by the reflector. All one needs to do is think of the huge searchlights I think they use this backfiring type technology

Lynx_Arc said:

You would need a very small emitter and a large reflector in order to eliminate light escaping that isn't properly refocused by the reflector. All one needs to do is think of the huge searchlights I think they use this backfiring type technology

Click to expand...

That is why in all my discussions/discourses about reflectors/spill/throw I have made it a point to state that a parabolic reflector only works perfectly with a point source emitter. Point being used in the mathematical definition of a position in space with no size. The closer our emitter comes to this ideal, the better the reflector performs. That is why for a while many small lights used the XP-E emitter, due to its small die size. Unfortunately, since the Lumens War has descended to the smaller lights, the XP-E is very seldom used these days in favor of its larger, higher output cousins.

For a given depth of reflector, a smaller diameter will produce less spill than a larger diameter. As a rule of thumb, the diameter of a reflector controls the amount of spill, and the depth of the reflector controls the size and intensity of the hot spot, and thus the throw.