# why are warmer temperature leds less bright than cool when hids are opposite?



## mr.lumen (Apr 6, 2012)

can anyone shed some light on this? much obliged.


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## ElectronGuru (Apr 7, 2012)

Dont know about HIDs but...


LEDs are naturally blue. Making them warmer (less blue) requires phosphors. These are like filters, but better. Rather than just screened, light energy is coverted from one color to another. The new color joins the rest of the original color, creating an average, the target color. Phosphors are not 100% effecient, so more phosphor = less output.


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## jtr1962 (Apr 7, 2012)

Warmer light has a higher percentage of long wavelengths. These come from phosphor conversion of blue light, as ElectronGuru said. The greater the difference between the primary wavelength and the converted wavelength, the greater the losses from the Stokes shift.


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## yifu (Apr 7, 2012)

In metal halide HIDs, the reverse happens. This is because the mixture contains halides of metals, including bromides, iodides and chlorides. Sodium is also used to increase the efficiency of the bulb and xenon as well because it provides more light (in the blue-violet range) at initial start up which is useful in automobile applications, where it was first utilised, in the 1990s.

Here is a chart of the typical HID spectrum. You would see that the peak in output is around the 583nm mark. This is EXACTLY the most prevalent emission spectrum of sodium when it is excited by the arc and the electrons jump from the 3p sub orbital to the 3s sub orbital. There are other emissions of sodium as well, such as a 3d to 3s (red) but the 583nm one is the most common. BTW the spectrum of the HID below is not continuous as it seems, it is a line spectra and by its definition is a series of lines, with black space between them. There are of course specialty HIDs like mercury arcs with xenon fill gas only, which produces band emission in the blue-violet/UV range but they are less efficient.

Out of all the fill mixtures, alkali metal based ones(or rather ones with alkali metals in them) are the most efficient(with sodium being the easiest to extract), hence sodium is used in most street lights and has a peak efficiency of around 130 lumens/watt. When you produce a "cool" white HID, you must reduce the amount of sodium in the mixture, thereby reducing the efficiency of the package. Either that, or you have to decrease the percentage of Na in the mixture, decreasing it's contribution in terms of lumens. Hope that helps!


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## slebans (Apr 7, 2012)

yifu said:


> In metal halide HIDs, the reverse happens. This is because the mixture contains halides of metals, including bromides, iodides and chlorides. Sodium is also used to increase the efficiency of the bulb and xenon as well because it provides more light (in the blue-violet range) at initial start up which is useful in automobile applications, where it was first utilised, in the 1990s.
> 
> Out of all the fill mixtures, alkali metal based ones(or rather ones with alkali metals in them) are the most efficient(with sodium being the easiest to extract), hence sodium is used in most street lights and has a peak efficiency of around 130 lumens/watt. When you produce a "cool" white HID, you must reduce the amount of sodium in the mixture, thereby reducing the efficiency of the package. Either that, or you have to decrease the percentage of Na in the mixture, decreasing it's contribution in terms of lumens. Hope that helps!




The efficacy for Metal Halide lamps is more in the 90 - 100 lumens per watt range - and that is before any ballast losses(further losses are incurred when the bulb is mounted in a fixture).
High pressure Sodium lamps are generally in the 125-150 lm/w range. 
Low pressure Sodium lamps can exceed 200 lm/watt.

Stephen Lebans


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## yifu (Apr 7, 2012)

Most metal halide HIDs that are in use are the ones that exceed the 1kW mark. Those, manufactured by the likes of Wolfram, General Electric or Osram etc have an efficiency exceed 100 lumen/w. But as i said, the addition of sodium (usually in the form of the alkali metal halide-sodium iodide) increases the efficiency, but most of that light output is near the 580nm range, which is warmer. This is the reason why modern HIDs are much more efficient that the carbon arcs of late or the mercury arcs of the past few decades, which had much cooler colour temperatures.


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## mr.lumen (Apr 7, 2012)

very interesting. does anyone know why leds are naturally blue? whats the science behind that? i get why making them warmer cuts the efficiency very similar to halogen headlamps that are "hid blue" because they just add a coating which blocks most of the warmer temperature light and shows the cooler temperature but cuts total amount of light emitted. so they look bluer but are definitely not as bright as standard. thanks guys!


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## yifu (Apr 7, 2012)

That's simple. (Maybe not quite) Most current white LEDs use a gallium nitride or indium nitride semiconductor base substrate, typically shortened as InGaN (although the LED industry is converting to cheaper options like silicon carbide). 

In my physics notes, it says that for this type of direct bandgap configuration, when the compositions are around In0.13Ga0.87N, the peak wavelength of around 402nm correlates to the energy gap between the conduction band and the valence bands in the semiconductor holes. This energy gap is the result of a photon assisted transition between the holes in the semiconductor, which produces a photon with the magnitude of the energy difference. Depending on the doping/concentration of In and Ga, this gap ranges from 400 to about 465nm. 

Look, this is quite complicated. If you want the whole story, ask a physics professor in electro-luminescence. I only know the basics of semiconductors. If you want the advanced stuff i can PM you PhD papers on this subject although if your uni has a subscription to Wileys you can find them yourself! It is very dry reading though.


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## jtr1962 (Apr 7, 2012)

mr.lumen said:


> very interesting. does anyone know why leds are naturally blue? whats the science behind that? i get why making them warmer cuts the efficiency very similar to halogen headlamps that are "hid blue" because they just add a coating which blocks most of the warmer temperature light and shows the cooler temperature but cuts total amount of light emitted. so they look bluer but are definitely not as bright as standard. thanks guys!


The coating isn't a filter which blocks some of the blue light but a _phosphor_ which converts it to longer wavelengths. This conversion process isn't 100% efficient, although it can exceed 80% efficiency. It gets less efficient if the blue light is converted to a spectrum which has more longer wavelengths (i.e. a warmer spectrum). That's basically the physics behind it. In short, a white LED is really a blue LED covered with a phosphor which converts some of the blue light to yellow. The combination of blue and yellow light appears white to our eyes. There are definitely not any filters involved.


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## blasterman (Apr 7, 2012)

Which leads me to the question as to why LED makers typically set the base blue dominant wavelength at 445-455 nanometers rather than 'cheat' and set it at 470-475nm, which can be done in manufacturing. Cree and Luxeon / Rebel seem to actually be drifting towards shorter wavelengths in the latest LED's with Rebels being even shorter in dominant wavelength in their white LEDs by a bit than Crees.

My thought process being that 470-475nm is significantly brighter in terms of visual lumens than 445-450nm. With most cool-white lighting applications being about raw lumen horsepower than color aethestics it would seem to make sense. Does the shorter initial wavelegnth of blue allow for more efficient stimulation of the secondary phosphors or something? Always wondered this. Obviously the reduction of elimination of amber/red can produce higher lumen production at the expense of CRI, but I've never understood why not 'cheat' on the other end of the scale.

As I understand it from a metal halide perspective, psuedo full spectrum halide bulbs that also have good efficiency are rather difficult and expensive to make because all the individual components do unpredictable things when in a plasma state inside that small capsule.


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## slebans (Apr 7, 2012)

yifu said:


> Most metal halide HIDs that are in use are the ones that exceed the 1kW mark. Those, manufactured by the likes of Wolfram, General Electric or Osram etc have an efficiency exceed 100 lumen/w.



I disagree with your two statements. 
The majority of MH lights in use are below 400 watts and the largest segment is 200 watts and lower. What majority market segment are you referring to where the MH bulbs exceed 1000 watts?

I stated that the nominal efficacy is in the 90-100 lm/w range. Yes, there are a few bulbs where the spec is 115-120 lm/w but that is not the norm and this value is the "initial lumens" rating. A couple of months of operation and you are well below 100 lm/w.

Stephen Lebans


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## blasterman (Apr 8, 2012)

I agree with Stephen in that the biggest market segment for metal halide is the 250-400watt range, although efficiency seems to improve as the wattage goes up.


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## yifu (Apr 8, 2012)

Well, let's face it, you wouldnt use a 400W HID as a beside light. HIDs are used only in commercial large space lighting solutions, airports, street lights, stadiums, movie production. In most common streetlights in Australia at least, the minimum wattage is about 600W high pressure sodium, in stadiums i have seen the big 2kW bulbs getting changed( a CPFer built a light around it, the bulb is like 30 cm long), in movie production, most big movie studios use Wolfram lights, whose lowest wattage HId bulb is 1200Ws. That leaves warehouses, Cree published a report some time ago stating that it aims to produce fixtures that replace the most common HID used-400W. Movie theatres generally also use at least a 10kW HID, mostly from Osram. The only places i have seen sub 400Ws being used are carparks, petrol stations and big stores like Costco.

THe reason larger wattage HIDs are more efficient is because the thicker lens allows for a higher pressure inside, allowing a greater concentration of fill gases in it. Movie projectionists who change out the 10+kW bulbs wear ballistic clothing in case they explode...As the higher the wattage the greater the chance of a catastrophic EOL(end of life


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## och (Apr 8, 2012)

yifu said:


> Well, let's face it, you wouldnt use a 400W HID as a beside light. HIDs are used only in commercial large space lighting solutions, airports, street lights, stadiums, movie production. In most common streetlights in Australia at least, the minimum wattage is about 600W high pressure sodium, in stadiums i have seen the big 2kW bulbs getting changed( a CPFer built a light around it, the bulb is like 30 cm long), in movie production, most big movie studios use Wolfram lights, whose lowest wattage HId bulb is 1200Ws. That leaves warehouses, Cree published a report some time ago stating that it aims to produce fixtures that replace the most common HID used-400W. Movie theatres generally also use at least a 10kW HID, mostly from Osram. The only places i have seen sub 400Ws being used are carparks, petrol stations and big stores like Costco.
> 
> THe reason larger wattage HIDs are more efficient is because the thicker lens allows for a higher pressure inside, allowing a greater concentration of fill gases in it. Movie projectionists who change out the 10+kW bulbs wear ballistic clothing in case they explode...As the higher the wattage the greater the chance of a catastrophic EOL(end of life



There are plenty of sub 100w metal halide lights. I have a 100W metal halide light in my backyard, many buildings utilize 100w around entrances and planters. And most modern car headlights use 35w metal halide bulbs. 

Metal halide bulbs bulbs however are not very practical for indoor lighting - their warm up time is very long you cant switch them on and off right away - they need time to cool down. I think eventually most metal halide lights are going to be replaced by LEDs. They have roughly equal luminous efficiency, but since most applications for metal halide are directional lighting they are very lossy. Directional LEDs deliver more lumens at the intended direction.


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## blasterman (Apr 8, 2012)

Curious if anybody can answer my royal blue -vs- standard blue question.

In the past five years or so I've seen an increase in the availability of high-end, track type directional HID lighting with very high CRI and under 100watts of power. Likely a response to color demanding halogen / Solux applications which are terribly inefficient. However, this might be too little too late because I'm not seeing a lot of interest in these type of fixtures and Solux still seems to still rule those applications...that is until we see more LED fixtures with higher CRIs.

I'm still impressed by the ability of metal halide to light a football stadium at night like it was daylight with >90 CRI color.


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## FRITZHID (Apr 8, 2012)

yifu said:


> Well, let's face it, you wouldnt use a 400W HID as a beside light. HIDs are used only in commercial large space lighting solutions, airports, street lights, stadiums, movie production. In most common streetlights in Australia at least, the minimum wattage is about 600W high pressure sodium, in stadiums i have seen the big 2kW bulbs getting changed( a CPFer built a light around it, the bulb is like 30 cm long), in movie production, most big movie studios use Wolfram lights, whose lowest wattage HId bulb is 1200Ws. That leaves warehouses, Cree published a report some time ago stating that it aims to produce fixtures that replace the most common HID used-400W. Movie theatres generally also use at least a 10kW HID, mostly from Osram. The only places i have seen sub 400Ws being used are carparks, petrol stations and big stores like Costco.
> 
> THe reason larger wattage HIDs are more efficient is because the thicker lens allows for a higher pressure inside, allowing a greater concentration of fill gases in it. Movie projectionists who change out the 10+kW bulbs wear ballistic clothing in case they explode...As the higher the wattage the greater the chance of a catastrophic EOL(end of life



i also kindly disagree, i have a 100w HM as a grow lamp for my seedlings since spring starts so late here, many of the small businesses around the area use wattages near this as well for sign and store front illumination, and recently i've noticed an increase in the # of 35-55w small HID MHs being used indoors in an effort to replace CCFL and Halogen semi-flood lighting. many of the gas stations around use 35-75w MH Minis as building perimeter lighting as well. so to say MH is in the +400w use mainly is incorrect.


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## och (Apr 8, 2012)

Metal halide pretty much provides natural daylight color, and with insanely high wattage capability, its no surprise. However, theres a HUGE loss of lumens with metal halide when it comes to purposes like lighting up a football stadium, since bulbs are spreading light in every direction, about 50% is lost in the reflector. This is why LED has a good potential of eventually replacing metal halide alltogether.


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## FRITZHID (Apr 8, 2012)

idk about that eather, since my spotlights are all HID MH's and they throw a LONG ways, WAY farther then LEDs can. smaller point source = throw. and even my old 400w HID homemade spotlight thru like a beast and it had an aprox 2.5' arc tube. it's all a matter of the quality of reflector. LEDs still have a LONG way to go before catching HID MH's output in the same space.


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## idleprocess (Apr 8, 2012)

yifu said:


> The only places i have seen sub 400Ws being used are carparks, petrol stations and big stores like Costco.



Those are far and away the biggest users of metal halide fixtures. Stadiums, set lighting, film projectors, etc are all lower-volume specialty uses.

In the US, it's fairly easy to source MH bulbs up to 400W at reasonable prices.


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## idleprocess (Apr 8, 2012)

FRITZHID said:


> idk about that eather, since my spotlights are all HID MH's and they throw a LONG ways, WAY farther then LEDs can. smaller point source = throw. and even my old 400w HID homemade spotlight thru like a beast and it had an aprox 2.5' arc tube. it's all a matter of the quality of reflector. LEDs still have a LONG way to go before catching HID MH's output in the same space.



While LED's are fairly close to being ideal point sources, they're probably never going to approach the brute-force flux levels that a HID arc can spit out. LED's are only scaling to about 10 watts or so (at the price of larger die sizes too) while HID's can reach into the kilowatts. LED's can pump out many thousands of lumens in parallel, which is fine for area lighting, but not so great for insane throw. HID is going to be around for a while when it comes to spotlights.


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## yifu (Apr 9, 2012)

och said:


> Metal halide pretty much provides natural daylight color, and with insanely high wattage capability, its no surprise. However, theres a HUGE loss of lumens with metal halide when it comes to purposes like lighting up a football stadium, since bulbs are spreading light in every direction, about 50% is lost in the reflector. This is why LED has a good potential of eventually replacing metal halide alltogether.


Not going to happen any time soon. HIDs might be the world's oldest electric light source (much older than incans even) but they're here to stay. To replace the light coming out of just 1 stadium HID, you need at least 1000 XML LEDs driven at full spec. The amount of electrical drivers and the heatsink required means its simply not feasible. HIDs do very well with heat and at around 1000 dollars per 10kw+ bulb, considerably cheaper than what's required to get the LEDs.


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## slebans (Apr 9, 2012)

yifu said:


> Not going to happen any time soon. HIDs might be the world's oldest electric light source (much older than incans even) but they're here to stay. To replace the light coming out of just 1 stadium HID, you need at least 1000 XML LEDs driven at full spec. The amount of electrical drivers and the heatsink required means its simply not feasible. HIDs do very well with heat and at around 1000 dollars per 10kw+ bulb, considerably cheaper than what's required to get the LEDs.



Look, I don't want to turn into the HID police -it's not my area of expertise- but you are off by a factor of almost 10. The majority of stadium light luminaries are MH 1000w or 1500w based bulbs. Additonally, there are significant losses due to the primary reflector/housing surrounding the bulb.

Stephen Lebans


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## Optical Inferno (Apr 9, 2012)

blasterman...I'll take a stab at it. The phosphors are "tuned" to certain activation wavelengths due to their chemical arrangement. Depending upon the phosphor, it may require a different wavelength for activation but the conversion efficiency will suffer. 

I am playing with some of the Intematix chroma-lit products and they are tuned to the 455nm. I'm guessing that the base of the phosphor is the same across the products (like neodymium or something) thus being tuned to the 455nm. Using another material to accept a maximum conversion efficiency at a longer wavelength would likely be too expensive as a material or processing procedure. 

Maybe someone else can fill in the blanks if I missed something...


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## blasterman (Apr 9, 2012)

Couple of points of contention.


> i have a 100w HM as a grow lamp for my seedlings since spring starts so late here



Which means you could provide the same growth PAR in LED at about 1/3 the watts. One thing HID's do suck at, and that's PAR....other than HPS, and not everything can grow under a single sodium emission line. With reef tanks we're getting 200 and 300% efficiency gains converting to LED, and I covered the red side of the arguement above.



> many of the gas stations around use 35-75w MH Minis as building perimeter lighting as well.



Several gas stations in town here have converted to LED fixtures, and the color and brightness improvement is astronomical. I'll happily post pictures for general comparison. As for <100watt HID fixtures, I don't recall seeing one in quite awhile. At lower wattages HID starts to lose efficiency and get's trumped by LED fixtures running at a fraction the wattage.



> Metal halide pretty much provides natural daylight color



By default, no. If you have a MLB stadium chances are it's lit with high CRI, >1000watt halides because your TV contract demands it. If you're a small high school in the midwest, or just lighting up a parking garage you're probably running lights in the 60-70CRI range. Even the worst Rebels and Cree cool-whites exceed that, and due to the shape of the LED spectrum, which is inherently smooth and doesn't have the jagged spikes of HID they tend to look better at the same CRI.



> The amount of electrical drivers and the heatsink required means its simply not feasible.



Heat-sink, yes, Thermal management, yes. We all know this is the achilles heel of scaling up LED because while the LEDs are getting cheaper metal prices aren't. However, the driver arguement is not the case.


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## bshanahan14rulz (Apr 9, 2012)

Optical Inferno said:


> blasterman...I'll take a stab at it. The phosphors are "tuned" to certain activation wavelengths due to their chemical arrangement. Depending upon the phosphor, it may require a different wavelength for activation but the conversion efficiency will suffer.
> 
> I am playing with some of the Intematix chroma-lit products and they are tuned to the 455nm. I'm guessing that the base of the phosphor is the same across the products (like neodymium or something) thus being tuned to the 455nm. Using another material to accept a maximum conversion efficiency at a longer wavelength would likely be too expensive as a material or processing procedure.
> 
> Maybe someone else can fill in the blanks if I missed something...



^ I think the main reason is that is the best phosphor they can use when they take into account things like efficiency, price, ease of manufacturing, etc. 

Perhaps a corrolary to that, and why companies were for a while looking at using shorter ~400nm as the pump source, is that photon for photon, a photon with a lower wavelength will carry a higher energy. Of course, that would mean that it takes more energy to make that photon too.

Also, side note, the hydroelectric dam, built for TVA here, that creates the J Percy Priest Lake, they recently switched their road lights on the damn from mercury vapor to LED :-D


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## djozz (Apr 14, 2012)

I wil have a go on this as well.
I can think of two reasons of why not to shift the base emitter-wavelength of the white led towards the 400nm:

1) It is desirable that the blue peak of the emitter itself contributes as much as possible to the brightness of the white led, since in this part of the spectrum of the led no energy is lost in conversion to longer wavelengths by phosfors. The human eye is however increasingly insensitive to light aproaching the 400nm (it is most sensitive to green and increasingly insensitive to blue and purple, in fact the the way the brightness is measured in lux (and its derivative lumen), takes this in account, greenlight contributes more to the 'lux-count' than blue or red), so if you shift your blue peak towards purple, it contributes less to the brightness.

2) In the conversion of light into longer wavelengths by the phosfors, there is a minimum amount of energy which is lost. This results in the fact that fotons produced by the phosfors can not have wavelengths very close to the intial wavelength of the emitter (I do not know a way to explain this better, sorry). This is why you always see a dip between the blue and green in the spectrum of a white led. If the base wavelength of the led is set to (say) 400nm, this dip will be right in the middle of the blue area, with no visible shorter wavelength light, resulting in a pretty worthless spectrum, without blue.

By the way, if you do not care about efficiency, and you want to build a led with a full spectrum in the visible area without major dips (and thus unprecedented good colour rendering, for a led), the best way would be to start with a base wavelength even a bit shorter than 400nm, say 360, and convert that to visible light with suitable phosfors. The dip will then be still in the invisable part of the spectrum between 360 and 400nm. Unfortunately this way you miss out the lux-contribution of the base wavelength, and moreover: currently, UV-emitters in the 360nm range are way less efficient than blue emitters. 

Does this lighten up things a bit??

Jos




blasterman said:


> Which leads me to the question as to why LED makers typically set the base blue dominant wavelength at 445-455 nanometers rather than 'cheat' and set it at 470-475nm, which can be done in manufacturing. Cree and Luxeon / Rebel seem to actually be drifting towards shorter wavelengths in the latest LED's with Rebels being even shorter in dominant wavelength in their white LEDs by a bit than Crees.
> 
> My thought process being that 470-475nm is significantly brighter in terms of visual lumens than 445-450nm. With most cool-white lighting applications being about raw lumen horsepower than color aethestics it would seem to make sense. Does the shorter initial wavelegnth of blue allow for more efficient stimulation of the secondary phosphors or something? Always wondered this. Obviously the reduction of elimination of amber/red can produce higher lumen production at the expense of CRI, but I've never understood why not 'cheat' on the other end of the scale.
> 
> As I understand it from a metal halide perspective, psuedo full spectrum halide bulbs that also have good efficiency are rather difficult and expensive to make because all the individual components do unpredictable things when in a plasma state inside that small capsule.


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## mr.lumen (Apr 14, 2012)

i notice you guys are talking about hid vs led for industrial lighting. im sure you have seen these but i found these led replacement lights for the high powered hids and thought they were pretty sweet! they cost almost double but use more than half the electricity so you would pay them off in no time from your energy bill. not to mention all the other benefits of leds. the heat sinks for these 14000 lumen lights are huge but not that much bigger than the light housing of a similar hid set up. 

http://www.superbrightleds.com/cgi-bin/store/index.cgi?action=DispPage&category=&Page2Disp=%2Fspecs%2Fhighbay.htm#photos


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## Roger Bannister (Apr 24, 2012)

mr.lumen said:


> i notice you guys are talking about hid vs led for industrial lighting. im sure you have seen these but i found these led replacement lights for the high powered hids and thought they were pretty sweet! they cost almost double but use more than half the electricity so you would pay them off in no time from your energy bill. not to mention all the other benefits of leds. the heat sinks for these 14000 lumen lights are huge but not that much bigger than the light housing of a similar hid set up.



Thanks for the link, _Señor Lumen_.

...Wow, look at the mark-up on those. Atrocious.

The newer COBs themselves can be had for less that $1/watt, even in small qtys for hobbyists like ourselves; that's a chunk of change for some metal, a heatsink, and a driver. Also, that's a lot of watts to be using _passive-only_ heatsink designs, esp. for the larger ones. Putting 200w (well, the % that doesn't get converted into photons, anyway) into a 'retrofit-friendly' radial heatsink? _Sheesh_.

(I hate retrofits...but what are you gonna do? They are the largest market, near-term. Too many compromises go into their manufacture and construction.)

Outside of CREE, most of the COB spec sheets still rate them at a Tj of 25°C. You still get more forward-facing lumens with LEDs, but expect both the lumens and end-of-life lumen maintenance to be significantly lower than listed, as with most 'marketing'. (At least CREE is getting it right, with their B/L @ 85°C for the newer XT-E, XB-D, and CXA.) I wouldn't count on ~70 lm/w and 48 LUX @ 15m with the larger ones.

Of course, you still have the 'throw' issue...I agree that for certain applications, you're just not going to see these replace HIDs anytime soon.


Roger


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