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I am thinking of using a high power ~50W IR led. I am wondering if LED IR is more efficient than halogen as is the case with visible light LED's? I couldn't find the light output of either IR halogen or LED so I can't compare products per watt.

I basically want to determine if using an LED is worth the cost and added complexity versus the power savings if any. The LED wavelength can be either 840nm or 940nm.

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  • \$\begingroup\$ There is no general answer, I can construct (and maybe find on the market) two pairs of both devices where in each the other is more efficient. \$\endgroup\$ – PlasmaHH Jul 20 '15 at 10:14
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    \$\begingroup\$ You have to compare the slice of the halogen spectrum that meets your needs vs. the slice of the IR LED spectrum that meets your needs. We don't know your function that relates wavelength to efficacy. \$\endgroup\$ – Spehro Pefhany Jul 20 '15 at 12:09
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    \$\begingroup\$ I'd say that power-consumption-vs-lumens-output, the LED would be somewhat more efficient. However, 50W isn't a very large lamp, and has relatively complex driving characteristics (temperature monitoring, heatsink, current limiting, DC converter, etc. Wouldn't want to dissipate tens of watts on a bias resistor.) AC halogens require zero driving circuitry and scale into the kilowatt range. So practically speaking, the LED would be a "novel idea" in my opinion. (Perhaps there is a paper somewhere describing some beneficial effects of narrow-band IR emissions on tissue?) \$\endgroup\$ – rdtsc Jul 20 '15 at 13:13
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    \$\begingroup\$ Halogens are MORE efficient than LED in selected parts of the IR spectrum. It deep-ends how wide a slice you want to accept. For narrow bandwidths LEDs are better. In whole visible range LED is >> halogen as halogen has much IR out. Halogen is 100% efficient overall as ALL energy in comes out as light and "heat". A GOOD narrow band LED at one wavelength puts out 1/3 to 1/2 of energy in as wavelength out. The rest goes to heatsink as widish band heat. If the heatsink IR out is not useful in your application it is lost. \$\endgroup\$ – Russell McMahon Jul 20 '15 at 14:26
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    \$\begingroup\$ @WhatRoughBeast I used to dabble in theater lighting back when halogen bulbs were the "hot" new thing: A thousand Watt halogen lamp typically would last somewhere between ten and a hundred times longer than the equivalent old-style incandescent bulb. I don't remember the chemistry, but the halogen in a halogen bulb is bromine or iodine and, at the high temperatures and pressures inside the quartz capsule, it somehow prevents tungsten atoms from "boiling off" from the filament. \$\endgroup\$ – Solomon Slow Jul 20 '15 at 17:11
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Halogens are MORE efficient than LEDs in selected parts of the IR spectrum if the selected portion is wide enough. It deep-ends how wide a slice of spectrum you want to consider useful.

For narrow bandwidths LEDs are better.
In whole visible range LED is much better than halogen as halogen has much more IR out than visible out.

Halogen is 100% efficient overall as ALL energy in comes out as light and "heat".
A GOOD modern (narrow band) LED at one wavelength puts out 1/3 to 1/2 of energy-in as wavelength-out. The rest goes to heatsink as widish band heat.
If the heatsink IR out is not useful in your application it is lost to you.
IF the LED heatsink IR is useful to you then it too is 100% efficient.
Odds are you do not want the LED's heatsink IR.

As you narrow the halogen bandwidth you use you use less of total output and "useful efficiency falls". When you drop under 1/3 to 1/2 of total energy in bandwidth you consider useful then LED is more efficient.

eg when using a halogen for optical lighting we consider a bandwidth that contains about 5% to 10% of the total energy out to be useful. So a modern LED is always more efficient for lighting at its design wavelength than a halogen is and more efficient in the whole optical band (all energy summed) than a halogen is.
If we use a halogen bulb to illuminate a typical silicon solar panel we find its efficiency RISES as a portion of the IR output falls in the panel's response range.


An (apparently) excellent reference: A major problem in trying to do useful things in this field is that, as in most areas involving people + healing / health / therapy / well being / feel good ... there is an immense amount of hype, hearsay, suspect claims, bad science and general rubbish to wade through. That is not to say that there are not very real and demonstrable benefits available - just that sorting the (w)heat from the chaff can be difficult.
This reference LED Light Therapy provides 29 pages of comment, reported results, and comments on investigations. It's not perfect, but at a quick glance it looks better than much that can be found. And it will probably address the OP's less than fully specified question better than any answer here can do. While the title suggests it's about LEDs it also deals well with halogen light use.
It may be educational to examine the sites usage of terms such as IR, heat and wavelength. Maybe not :-).

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    \$\begingroup\$ You really can't say it's 100% efficient. Heat is a waste product except where it is created from IR hitting external objects. IR is not the same as heat. If you take waste products into account then everything is 100% efficient. Any idea what % of the energy is released as IR as opposed to heat generated in the halogen bulb? \$\endgroup\$ – DominicM Jul 21 '15 at 13:39
  • \$\begingroup\$ @DominicM Your reply reflects a lack of knowledge & understanding of the system that you are dealing with and a lack of definition in what you are asking. A lack of knowledge & understanding is unavoidable for all of us BUT attempts should be made to minimise it when resources are provided which help us to do so. | Heat is IR and IR is heat for practical purposes in this context. IR is just a convenient catch-all name for electromagnetic energy which is not visible to the human eye and which is of longer wavelength than visible light by a factor of not more than a few times. .... \$\endgroup\$ – Russell McMahon Jul 22 '15 at 15:00
  • \$\begingroup\$ ... For a halogen bulb the vast majority of energy which leaves the filament does so as electromagnetic energy. A small %age is transferred by convection by the inert gas in the bulb. When it reaches the envelope some IR energy is absorbed. This is then either reradiated at a longer IR wavelength than it was absorbed at or removed by air convection. You could argue that the convection process at base as also largely due to radiation transfer into air the boundary layer. THe very large part of the output of a a tungsten bulb is designed and designable (unlike an LED where off design .... \$\endgroup\$ – Russell McMahon Jul 22 '15 at 15:04
  • \$\begingroup\$ ... wavelength heat emission wavelength varies with heatsink design etc. | The point is that you have asked about light therapy, you now that a halogen lamp can serve the purpose, but you have not indicated what range of wavelengths you consider to be useful. In the extreme case ALL may be and the halogen IS near 100% efficient. Only when YOU specify what range is useful to you can anyone address the efficiency question well. The spectrum of halogen lamps is well described on the web and you should look at some resources and comment on them as part of the question. \$\endgroup\$ – Russell McMahon Jul 22 '15 at 15:12
  • \$\begingroup\$ In practical terms heat generated in the heat-sink/bulb is lost as it is likely going to be very different wavelength or reflected in the wrong direction. IR is not the same as heat. Different word, different meaning. By your logic since IR = heat then visible light = IR. IR is radiation in a specific range of wavelength just like visible light etc... Not all heat is in the IR range, halogen bulbs also release visible light which is not IR and so the bulb cannot be 100% efficient even in theory. \$\endgroup\$ – DominicM Jul 22 '15 at 19:23
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For the best IR LED you may find OSRAM OSLON series, SFH 4715A and SFH 4715AS. These are close to 50 %. With similar output Halogen IR will be either visible or will be very big compared to IR LED. Therefore the IR LED is the optimal choice if you are to focus the IR on distance. Otherwise you are well served with the Halogen.

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