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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.

DominicM
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  • 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. – PlasmaHH Jul 20 '15 at 10:14
  • If the aim is to mimic heat, then heat (AKA halogen) is probably better than the relatively narrowband LED, which may have a different effect. –  Jul 20 '15 at 10:20
  • Well the wavelength is about the same or at least it's what I want (940nm or 840nm will work for my purposes). So would a halogen bulb produce about the same IR light output as the LED per watt? While heat is what gives the healing effects it has to be in the form of IR light to penetrate the skin. – DominicM Jul 20 '15 at 10:34
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    You have to compare the slice of the [halogen spectrum](https://en.wikipedia.org/wiki/Incandescent_light_bulb) that meets your needs vs. the slice of the [IR LED spectrum](http://www.ccs-grp.com/s2_ps/s1/s_02/ir/images/1_img_12.gif) that meets your needs. We don't know your function that relates wavelength to efficacy. – Spehro Pefhany Jul 20 '15 at 12:09
  • I don't think comparing the spectrum would work as it does not show how much of a watt is actually emitted as IR radiation as opposed to heat in the chip / bulb. Spectrum wise I believe both halogen and LED emit IR in a narrow enough range to be useful for my purpose so even if they are significantly different the IR should be useful in both cases. btw the halogen spectrum links to incandescent wiki page which doesn't have a spectral graph. – DominicM Jul 20 '15 at 13:03
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    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?) – rdtsc Jul 20 '15 at 13:13
  • @rdc I am not worried about driving it as I already have drivers that I use for visible light LED's, it's the high cost of IR led and extra cost of heat sink. There are cheap IR led light that are used for medical purposes so it can work. After doing some research I think I will go with red LED (620nm) as IR is not as beneficial for my purposes as I thought. Red led is also 10 times cheaper so the cost in not an issue here. Would still like to know the efficiency of IR LED vs halogen if someone has this info. – DominicM Jul 20 '15 at 13:52
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    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. – Russell McMahon Jul 20 '15 at 14:26
  • Some halogen bulbs with built-in reflectors have a dichroic reflector designed to pass the infrared portion of the spectrum, not reflect it. This makes their light less "hot" for the people below, the heat is rejected into the ceiling. Wouldn't help you of course. – tomnexus Jul 20 '15 at 14:47
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    Bear in mind that, relative to non-halogen incandescent bulbs, halogens are less-efficient IR producers. The entire purpose of halogen technology is to allow the filament to run hotter without reducing lifetime, which produces a greater fraction of the emitted energy in the visible spectrum - the bulb is brighter for the same total power. The flip side of this is that less IR is being emitted for the same total power. Since neither type is particularly efficient as a visible emitter, the degradation in IR efficiency is not great. – WhatRoughBeast Jul 20 '15 at 16:08
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    @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. – Solomon Slow Jul 20 '15 at 17:11
  • @jameslarge - Actually, it doesn't. What happens is that the tungsten attempts to condense out on the quartz envelope. Instead, it gets bound to a halogen atom and the gaseous compound circulates in the lamp. Eventually it hits the hot filament, dissociates the compound, and the tungsten condenses on the filament, renewing it. You can tweak the process, choosing either higher filament temperature/brightness at the cost of lifetime (still higher than non-halogen) or go for somewhat less brightness than is possible but longer lifetime. Either approach can be economical. – WhatRoughBeast Jul 20 '15 at 17:18
  • @DominicM you *may* find the addition to my answer highly useful. Hopefull so, anyway. – Russell McMahon Jul 23 '15 at 06:10

2 Answers2

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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 :-).

Russell McMahon
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    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? – DominicM Jul 21 '15 at 13:39
  • @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. .... – Russell McMahon Jul 22 '15 at 15:00
  • ... 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 .... – Russell McMahon Jul 22 '15 at 15:04
  • ... 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. – Russell McMahon Jul 22 '15 at 15:12
  • 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. – DominicM Jul 22 '15 at 19:23
  • I also did say that 840 and 940nm would both work so anything way off this range is not useful. There is no data that tests the effectiveness of IR wavelengths precisely as it would be obviously almost impossible considering the number of combinations of wavelengths and human body related variables. Studies often test more commonly available wavelength such as found in common IR devices. – DominicM Jul 22 '15 at 19:25
  • @DominicM I suggest you reread what I have already written and, as suggested above, look at some halogen spectra. I suggest using (eg Google's) image serach as a superb way of finding relevant material. I could LMGTFY but it seems likely that that would be throwing good input after bad. – Russell McMahon Jul 23 '15 at 04:44
  • I looked at some data but it doesn't seem like there is a relatively simple way to get a decent approximation. I will be going with red led as IR is not as beneficial as I thought. I did read the link you posted in your edit before and yes it is quite useful. As far as the question though I really wanted to get a rough idea of how much more/less usable IR I can get out of an LED vs halogen. Please edit the answer so it does not say halogen is 100% efficient and IR being the same as heat so I can accept it, thanks. – DominicM Jul 23 '15 at 12:49
  • @DominicM It's up to you whether you wish to accept it. THe 100% statement is 100% correct in the context that it is made. Obviously it's not correct for a selected portion of the output spectrum, BUT that was the point of me using the 100% figure - until YOU plug in some actual figures re what is acceptable npobody else can say what works for you. | Does "840 nm and 940 nm would both work" mean that eg 790 to 990 are ok (50% beyond the difference between them, or do yu accept only peaks at 940 and 940 and, if so, how wide, and should thse be weighted when looking at halogen? – Russell McMahon Jul 23 '15 at 13:08
  • @DominicM And sure, heat may not be IR when it's vibrational energy in a solid, but common usage is that EM radiation on the long wavelength side of visible is usually called heat for convenience (and no, I nevre defined visible as IR), and yesd, visible light can be though of as heat if thermal gain is your only aim and you have eg a CW visible output LASER as your source, and ... . SO in the ill defined context changing terms is pedantry and more liable to obscure than assist. | – Russell McMahon Jul 23 '15 at 13:13
  • ... I thought that last reference went an amazingly long way towards addressing the question. Whether what he says is science or mumbo jumbo I know not. but it sounds good :-). – Russell McMahon Jul 23 '15 at 13:13
  • Didn't you add the reference? Yes it is a good resource and I have read parts of it before I asked the question. I does not address the question itself as it does not compare efficiency or effectiveness of LED vs Halogen. – DominicM Jul 23 '15 at 13:23
  • Sorry but saying halogen is 100% efficient is oxymoron. Yes technically it is true in that energy cannot be lost but the word efficiency refers to the percent output of useful / wanted energy vs. waste / unwanted energy. It is assumed and there is no point in saying an LED is 100% efficient and incandescent light bulb is 100% efficient and... I the case of a white LED the light is useful energy and heat is a waste product. In a resistive heater the heat is useful while a small amount of light output is not. – DominicM Jul 23 '15 at 13:29
  • The fact is nothing is 100% efficient at converting one form or energy into another, there is always losses in the form of unwanted energy forms. What you said is IR is the same as heat. IR is radiation in a specific range and like any type of radiation is capable of carrying heat energy but is not heat itself. Halogen is not 100% efficient even at full IR range, there are losses in the form of visible light and like you agreed IR is not the same as visible light so since halogen produces IR AND visible light it CANNOT even in theory be 100% efficient. – DominicM Jul 23 '15 at 13:39
  • @DominicM As you go through life do you find that a more than usual percentage of people are argumentative and advance illogical arguments and keep saying stupid things without foundation despite you correcting them repeatedly. As eg it seems I do? If so, there may be findable reasons for such a skew existing. If not, it just must be flaws in my logic, my understanding, and my listening and my refusal and or inability to take apposite repeated correction. It happens, sometime, I'm told. – Russell McMahon Jul 23 '15 at 14:53
  • I have no idea what you are trying to say mate. If you believe I am wrong then please, by all means explain your reasoning as I am always open to learning new things, otherwise you are just being a troll and wasting people's time. – DominicM Jul 23 '15 at 18:28
  • [**Just being a troll and wasting people's time**](http://electronics.stackexchange.com/users/3288/russell-mcmahon) hmmm. Maybe – Russell McMahon Jul 23 '15 at 20:02
  • Wow, hard to believe the arrogance of some people... – DominicM Jul 24 '15 at 12:03
  • @DominicM Yes. Indeed. That thought did cross my mind, but I tried to suppress it as unworthy :-). | Suggestion: There is some material of likely value to you in the prior material that I have written. I suggest that you read through what I wrote, ignore obvious generalisations and avoid the easy enough trap of adding words or taking away words that are not there, and you may find it useful. eg where I don't say "IR" regarding halogen output, avoid the easy trap of seeing "IR" in what I wrote - halogen output can be considered EM energy radiant energy for practical purposes - from UV .... – Russell McMahon Jul 24 '15 at 14:29
  • @DominicM .... through visible and deep into IR. Halogen bulbs are used for many purposes and **for practical purposes** essentially 100% of the energy exits the bulb as EM radiant energy. There is SOME as convection and a small amount of conduction via the base (you would not want to hold one that had just been on) and odds are a small amount of audio from mains "hum" but its close enough for engineering purposes to approximate by saying that 100% of the energy leaves via the envelope as radiant EM. This is not true of LEDs. The very best send more that 50% of the input energy as .... – Russell McMahon Jul 24 '15 at 14:32
  • @DominicM ... narrow bandwidth (or phosphor reradiated) EM but the remainder is "heatsunk" in various ways. So if you are eg drying silk screen prints (as a friend of mine does) then essentially 100% of the halogen energy gets used. A LED can not compete. As the bandwidth that you care about narrows the % of energy in it falls and we say that the halogen's efficiency has dropped. This is not true per se - it just means we do not want some of it. If we want visible light we find only about 5%-15% of the energy is there so we say the halogen bulb is 5% to 15% efficient. If we want just long .... – Russell McMahon Jul 24 '15 at 14:38
  • .... wavelength non visible EM we say it is about 70%+ efficient. If we want UV it may be < 10% efficient. The bulb has not changed - just our spec. If we want two ranges in the IR for medical purposes we need to know where they are and how wide. If we say eg 840 & 940 nm - how much relevant energy lies there depends on if we accept an eg +/- 10 nM band or say 790-990 nM or whatever. Until we state what band is useful the efficiency question can't be answered. If we ask the question and it is ignored and we do that several times and still it is not answered it is not possible to address .... – Russell McMahon Jul 24 '15 at 14:42
  • .... the question. Just "around 840 & 940" is not enough. Also, if we look through related literature we may find that other wavelengths are said by some to be as good. If we accept that then a wider range can be included in our acceptable range figure and the halogen efficiency gets "magically" better. Without such decisions we have and can have no clue what the answer will be. If we decide to not address this uncertainty we are deciding by definition to not be asking a real question. Alas. – Russell McMahon Jul 24 '15 at 14:45
  • Thanks for actually addressing the points I made before. You have pretty much made the same points as I did in the previous comments. I didn't update the question because there simply does not appear to be a practical enough answer to my question. Not enough data on effectiveness to pick a useful IR range and too many variables to calculate efficiency for a given use. What I learned that halogen is a better choice mostly because it is at least an order of magnitude cheaper and simpler too. I will go with red led instead of IR as red may actually be more effective. – DominicM Jul 26 '15 at 19:00
  • Regarding efficiency, yes halogen can get close to 100% EM output, though still not that close since if the bulb can get that hot then there's a non-trivial amount of energy being released by conduction/convection. Even if we assume 100% EM output, it still cannot be said to be 100% efficient since it is an "IR light bulb" and not an "EM light bulb". With "IR light bulbs" we only care about the EM radiation that falls within the IR range of the EM spectrum. If you could edit your answer to reflect what you said in the last few comments, I would accept it, thanks. – DominicM Jul 26 '15 at 19:11
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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.

Søren Stig
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