# diffusing light from an led



## doctaq (Aug 5, 2010)

i feel like one of the major problems with leds breaking into standard house lighting is the narrowness of the light. led light bulbs almost always come with optics that tighen the beam making for a smaller brighter area, which i think is the opposite of what useful light or at least comfortable light is. 
it seems to me that one of the major ways of getting around this as cree uses in one of thier fixtures is to aim the light away and reflect it back to the original direction, why are there no optics that spread the light instead of focusing it?
i want to change my house over to led but dont want to pay 90 dollars a fixture, i can definateley diy. any suggestions? im thinking that i might try the reflecting idea.


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## EZO (Aug 5, 2010)

I've been intrigued by this idea as well. Sooner or later we will all be lighting our homes with LEDs. Don Mcleish, (McGizmo) the well known CPFer and custom flashlight designer extraordinaire has a web page where he features the LED lighting ideas and designs he has incorporated into his own home. (Who else?) Very interesting examples of direct, indirect and reflected light. I believe he has most, if not all of his home running solid state lighting.
http://www.dmcleish.com/MauiHome/


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## blasterman (Aug 6, 2010)

> why are there no optics that spread the light instead of focusing it?


 
While there a lot of retrofits using highly focused emitters as you rightfully gripe about, the few getting a lot of good press like the Ecosmart we've been talking about use a diffusion dome. While this limits the over-all amount of diffusion because of it's small size, it's roughly on par with a frosted light bulb in terms of softness.

I've spent a lot of time working out how to fix the 'specular' nature of LEDs for better aethestics, and the physics are rather interesting. 

Basically, you have three ways to diffuse the light of a point light source like an LED. You can either (1) diffuse it via frosted plastic (or micro faceted materials). Or, (2) You can reflect/bounce the light off a high albedo surface such as a white ceiling or panel. Or (3) you can use lots of LEDs spread out to simulate a larger light source such as LED strips.

Retrofit bulbs are going to be forced to shine through diffusion plastic given their restricted size, but the good thing is this is cheap to do and high tech materials with high transmission rates are being developed as we speak. This is the same stuff being used for small diffusers that clip over LED optics.

LED strips are obviously all over the place, but have some practical / aethestic limits such as needing it placed far enough away so you don't get annoyed with a dozen shadows of your pencil when you do a crossword puzzle. Or, combine a mild diffuser over the strip.

Reflection based light sources are perhaps the most intriguing given they have a huge amount aethestic potential even though the suffer the greatest efficiency loss. This is what I've been working on, and like the fact you've been thinking about as well. Shows I'm not off my rocker. If you think about it, a simple white lamp shade over a standard incan does a pretty good job generating nice room light, and that's kind of my standard (minus the crappy yellow bulb).

McGizmo's house has some cool design ideas, but over-all my impression of it is a lot of accent light that doesn't produce enough direct light. Not everybody wants to paint their walls white to bounce LEDs. So, I've tried to figure out how to localize very diffuse light, or direct it in a way similiar to a nice lamp shade, but optimized for LED.

One idea I'll throw at you for a DIY project is a floor standing reflection lamp. Build a frame of wood, or wrought iron (doesn't matter) about 5-6' high and maybe 10" square. At the top, sit a 12" piece of ceramic tile with the brightest, glossiest surface you can find. Underneath the tile pointed up sit a big heat sink with about 1,000 lumens of either Cree or Bridgelux emitters shooting up at the tile. Build a narrow frame around the sink to hide the emitters and the sink. I built a mock-up of this and it produces a huge sphere of down firing soft light that's more local than ceiling bounce and hence a lot brighter.

Lotsa ways to play with reflection and get stellar light from LEDs, but you aren't going to find it in retrofits, and commercial fixtures are fighting to have the best efficiency specs and not most pleasing light. So, be creative and DIY. LEDs don't have to be ugly.


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## doctaq (Aug 6, 2010)

thanks fellas, i looked through the house thread and its pretty awesome, i like the fountian especially. i think the most pleasing light is reflective in his use

crazy idea but what if i used a combination of something frosted and a concave lens to diffuse the light?


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## blasterman (Aug 6, 2010)

Won't matter. For diffusion, it's the size of the light source / optical source that matters. If you have a 3" lens it doesn't matter how heavy you diffuse it because it will provide the same effect.

For more diffusion the light coming from the emitter has to either bounce or be diffused through a larger source.


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## jashhash (Aug 7, 2010)

what you need is an led version of one of these: 
http://thedomesticfringe.files.wordpress.com/2009/08/100_4335.jpg

You know looking at the pictures from http://www.dmcleish.com/MauiHome/ as mentioned by EZO, it all seems kind of dim in appearance. I have noticed a similar phenomenon once when I built a 40 watt LED module using ten XP-G. By all means it is super bright at around 4,000 lumens it should be as bright as a 250 watt halogen lamp. But for some reason it just doesn't feel bright... It's hard to explain... but i just feel incredibly disappointed.


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## saabluster (Aug 7, 2010)

blasterman said:


> Basically, you have three ways to diffuse the light of a point light source like an LED. You can either (1) diffuse it via frosted plastic (or micro faceted materials). Or, (2) You can reflect/bounce the light off a high albedo surface such as a white ceiling or panel. Or (3) you can use lots of LEDs spread out to simulate a larger light source such as LED strips.


One other way is homogenizing light pipes. This is far more efficient than bouncing it off a white panel. There are many ways to implement this and they may also need to use a frosting at some point but the amount of frosting needed can be drastically reduced. Combining this with holographic diffusers can yield highly efficient fixtures with very high quality light since this allows the mixing of color LEDs as well.


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## MikeAusC (Aug 7, 2010)

doctaq said:


> i feel like one of the major problems with leds breaking into standard house lighting is the narrowness of the light. led light bulbs almost always come with optics that tighen the beam making for a smaller brighter area, which i think is the opposite of what useful light or at least comfortable light is.


 
All high-power LED emitters have a beamwidth of 90 to 120 degrees, so there's no optical reason for having a narrow beam for house lighting.

The reason fixtures have a narrow beam, is because afforable LEDs put out much less light than a very cheap incandescent. If you spread the light widely it becomes so dim, no-ones interested.


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## EZO (Aug 8, 2010)

jashhash said:


> You know looking at the pictures from http://www.dmcleish.com/MauiHome/ as mentioned by EZO, it all seems kind of dim in appearance.



I would tend to agree, there is a feeling of dimness but there is something else going on in these images that I think represents one of the central hurdles to the adoption of LEDs for home lighting. As cool as Don's ideas and designs are, something seems "off". I don't know, but it feels as if it could potentially be unpleasant to live under such lighting conditions on a long term basis. I'm talking about ambiance, mood, modeling, shadow quality, and color temperature/CRI. A few of the settings have a light quality that seem as if flesh tones could look almost ghoulish (for lack of a better word, here). Actually, some of the applications look highly successful, but others, less so. Don touches on this subject a bit on his web page when he discusses the issue of CRI challenges with food preparation. 

On the other hand, as a photographer my observation of the images on Don's web page is that they are all quite underexposed, even the ones that are not trying to show off LED lighting and so some of the perception of dimness and other issues are because of that. The actual experience of being in Don's home witnessing the actual lighting may be very different than what we are seeing.

Don should not feel bad if his photos don't look quite so good. As a professional who has a lot of experience shooting complex mixed lighting in architectural interior settings I can tell you that it can be one of the most challenging things to photograph. It can be especially difficult to obtain a well exposed image that conveys the true ambiance of a scene as your eye might see it. This is made even more difficult with today's digital sensors that have fairly limited exposure latitudes, dynamic range and straight exposure curves when compared to film. It is simply impossible to shoot a simple photo where you expose for a brilliant light source like LEDs and expect the dimmer areas of the scene to be properly exposed as well.


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## McGizmo (Aug 8, 2010)

Hi guys,
I just saw this thread and figured I'd add my 2 cents. First off, I am not sure how well my photos represent the reality involved. I suspect that as some have commented that my exposures of the images are on the dark side. I based all of these exposures on how the images appeared on my laptop when I processed the images. I often find that when I get prints made of one of my images that the print is darker than it should be. By the same token, I believe I am biased towards underexposure anyway. :shrug:

Additionally, I wanted to understate the effectiveness of the LED's if anything because I would feel remiss should someone attempt to model lighting after what I showed and come to the conclusion that the lighting resulting was less than anticipated.

No matter.

In terms of LED replacing incandescent there are obvious considerations and some hurdles to overcome. If you want to replicate the incandescent feel then color temperature and CRI must be addressed as well as overall flux generated.

Multiple distinct light sources will give you mutilple shadows and this is really annoying compared to a few larger sources of light. Diffusion or reflection mixing of the sources can overcome this issue to a reasonable extent. I think two materials that should be considered in LED fixed lighting are the MPET reflective plastic as well as one of the holographic diffusing films as mentioned (POC's LSD film is one example).

When I did my house, I was working with LED's that are not close to today's efficacy nor were they of high CRI relative to what you can get today. I have also learned a lot from mistakes and false assumptions! 

I have the materials on hand and a better idea of lighting now than I did back then and I could replace and re do my interior lighting if I wanted to. Frankly, I am quite satisfied with what I have and don't feel compelled to redo it at this point in time. 

If for what ever reason I had to start over and fresh there are a few key considerations I would embrace this time around. First and foremost is one that I don't have a solution for at present and when a solution does exist it is likely that I will revamp my interior lighting. That consideration is one of viable dimming. My vision is one where there are simple drivers available like the Xitanium but they have integrated in them a 3 level output similar in UI to that which I enjoy in the 3S converters I presently build my lights with. I really believe a LED system should be designed where you have three levels: overly or excessively bright, ideal and low. Frankly, I am just waiting for some company to recognize the utility in such a driver and once they become available I will again look at fixed lighting applications and get back into playing with them.

The other considerations for me are those of high CRI and effective diffuse flood and fill, within the rooms. Ideally there should be no hot regions or dark shadows and although such an ideal may not be realized there is no reason not to attempt to approach it. Specific task regions requiring greater light should be approached individually if efficiency is at all a concern. 

New construction and custom installations of lumanares are a different animal than reasonable retrofitting in rooms that were built with a single overhead fixture and one switched wall outlet for instance.

To the OP, I think most LED's have reasonable distribution without needing or using a secondary optic unless the application is that of a very efficient task specific lamp such as a reading light. To gain sufficient flux may well require multiple LED's and if that is the case it is likely that diffusion either direct or indirect by bounce is appropriate to reduce the effect of multiple point sources of light. Bunching the LED's in tight clusters can aid in reducing multiple shadow lines but this may be contrary to spreading the sources out such that they can more evenly illuminate a space where distance to targets is significant. The albedo of the surrounds is a very significant factor.

*EDIT*

Hi guys,
I should have looked at my web page before commenting. The primary lighting I have in living room, kitchen, bedrooms and bathrooms is not depicted effectively at all on that web page. If it were, you would see reasonably illuminated messy rooms not worth viewing or of any interest! Not to mention embarrassing for the owner! :nana: The images are clearly underexposed and focus on the light fixtures themselves and not what they are in place to illuminate; much like a beam shot on a white wall is exposed to give some feel for the beam itself and not the wall.


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## blasterman (Aug 8, 2010)

> Combining this with holographic diffusers


 
This is still diffusion - which qualifies as diffraction. If the light goes through a medium it's transmission which is type (1). However, the physics are same in that a given light source when diffused/difracted is limited by the size of that diffuser. If you want a softer light source, it has to be bigger. You also want the light coming from that diffuser to be as randomized as possible without losing efficiency. This is why milk plexi has such a terrible efficiency ratio, but it scrambles a point light source pretty good and yields soft light. Holographic films (I used to work with them years ago) would function about the same way as a fresnel lens, just smaller order ridges. Also, if the diffraction ridges are too small they'll start splitting up the light like a prism.


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## saabluster (Aug 9, 2010)

blasterman said:


> This is still diffusion - which qualifies as diffraction. If the light goes through a medium it's transmission which is type (1). However, the physics are same in that a given light source when diffused/difracted is limited by the size of that diffuser. If you want a softer light source, it has to be bigger. You also want the light coming from that diffuser to be as randomized as possible without losing efficiency. This is why milk plexi has such a terrible efficiency ratio, but it scrambles a point light source pretty good and yields soft light. Holographic films (I used to work with them years ago) would function about the same way as a fresnel lens, just smaller order ridges. Also, if the diffraction ridges are too small they'll start splitting up the light like a prism.



Congratulations you can read. Yes indeed diffusion means diffusion. It is not however required by the method I mentioned and that method was not mentioned in your 3 ways to diffuse.


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## McGizmo (Aug 9, 2010)

blasterman said:


> .......
> 
> The LED orientated Mean Wells have 10v external dimming options, and you could hook an arduino controller to them and do all kinds of unlimited goofy things.......



I am not interested in all kinds of unlimited goofy things or the complication of external controlers likely requiring additional wiring. My comment was focused on simple replacement of existing houshold A/C incandescent lamp fixtures with LED fixtures that could be powered on and off by existing simple toggle switches already in place; powered not only on and off but signaled through the same switch to come on in various power levels.


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## doctaq (Aug 9, 2010)

thanks guys
i am going to try a few things later on a get back to you guys
the holographic diffusing is interesting and i will look into it, even if the diffuser was only 2 inches, i still feel like that would be infinateley better than a naked led which would be very harsh on the eyes, as for the wacky dimming, i think that could be an interesting thing to play with, maybe for a lounge/ bachelor den area, maybe even with wacky colors where you dont need super bright even illumination all over the room. my room at home is full of aquariums and is super bright during the day, at night i have a red spot on the tank for night time viewing and a very dim incan (4w) on the other side of the room (soon to be replaced by one of those wacky dimmable remote led bulbs that change colors) since i dont want a bright room at night anyways as not to wake my tanks. it takes some getting used to but i wouldnt have it any other way now. 
of course this doesnt represent how a whole house should be lit. for now i am interested in single bulb retrofits running off of AC, it would be a bit of a strech for me to wire up an led driver to the wires within the wall, i dont know enough about house wiring to trust myself to this just yet. 
would holographic diffusion blend different colors? maybe allow me to mix some colored leds with white to bring color temp up or down as i please?
does anyone have any reccomendations as to where to buy some in small amounts just for testing?

thanks CPF


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## EZO (Aug 9, 2010)

McGizmo said:


> The images are clearly underexposed and focus on the light fixtures themselves and not what they are in place to illuminate; much like a beam shot on a white wall is exposed to give some feel for the beam itself and not the wall.



McGizmo, Thanks for your interesting reply. I hope you didn't mind my little critique of your photographs. I've read enough of your threads and looked at your web site enough to know you are a knowledgeable & skilled photography buff or more and I have really enjoyed your masterful underwater photography and beautiful shots with which you present your remarkable flashlights. As a guy who has been doing photography for 50 years now I know that not every image is a prize winner.

My own approach when photographing an object is to try to capture if at all possible, what the object does along with the object itself, which of course, in the case of a light fixture is to illuminate. As I've implied previously, this can get somewhat complicated, involving supplementary lighting, filtering for color correction, multiple exposures, HDR technique and other "tricks". Shooting what are essentially "snapshots" of works in progress of home installations is an entirely different kettle of fish.

Many years ago I studied under Norman McGrath, perhaps the premier architectural photographer working in the US today. Both his exterior and interior captures are quite remarkable but it is the interior shots under artificial and mixed lighting that are most relevant to this thread. Of course, I'm kinda' new here at CPF and I realize that I run the risk of straying too far from the original subject of this thread but after thinking about it for a bit I decided that diffusing light from an LED is ultimately about the quest to create pleasing interior lighting and McGrath's web site features some fine examples of interior lighting design as shot by a master so I include the link for anyone interested in taking a look and hope you'll indulge me.



McGizmo said:


> The primary lighting I have in living room, kitchen, bedrooms and bathrooms is not  depicted effectively at all on that web page. If it were, you would see reasonably illuminated messy rooms not worth viewing or of any interest! Not to mention embarrassing for the owner! .



McGizmo....Go clean your room!


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## blasterman (Aug 9, 2010)

saabluster said:


> Congratulations you can read. Yes indeed diffusion means diffusion. It is not however required by the method I mentioned and that method was not mentioned in your 3 ways to diffuse.


 
If the light is passing through something, then it's transmission. No reason to be a condescending a-hole about.

Light is either passing through something, or bouncing off it. The only other possibility is bending it with a gravitational field, which isn't likely.

Holographic diffusion works like a fresnel lens, except closer on wavelengths of light. It's a solution in search of a problem and so far I haven't seen it implemented on any commercial fixtures. Feel free to put a piece of holographic film over a flashlight, and a standard plastic diffuser, and note there isn't much difference is the spread of projected shadows.



> I am not interested in all kinds of unlimited goofy things or the complication of external controlers likely requiring additional wiring.


 
Then I'll delete my response and you can figure out another way to do it with Xitaniums and Cree.


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## Roland (Aug 9, 2010)

To widen the beam of the led PETZL uses what they call a "wide angle lens" which can be placed in front of the led:
http://www.petzl.com/en/outdoor/myo-series/myo-rxp

It is made from plastic and works really well on those led lights. Possibly with a glass cutter pieces of facetted glass could be cut to obtain the same effect.


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## McGizmo (Aug 9, 2010)

blasterman said:


> .....
> 
> 
> 
> Then I'll delete my response and you can figure out another way to do it with Xitaniums and Cree.



Your comment had merit for the OP and no reason to delete it. I would have simply stayed out of this thread and left it to you experts but I saw my crude and humble web page mentioned and commented upon so I spoke up. My page does not illustrate the actual illumination provided by the fixtures at all beyond the landscape shots outdoors.

The OP has just stated that he is presently looking at solutions where he can replace an incandescent bulb with a LED alternative. I am of the opinion that to be fair to the LED one needs to not just replace a bulb but replace the fixture itself, in most cases. This is primarily because an incandescent fixture is designed with the intent of isolating the heat generated by the bulb and a LED needs to gift as much of its heat generated as possible to its host. Replacing the fixture itself is not necessarily trivial but it can be pretty straight forward. 

In regards to diffusion and blending light from multiple sources, I think the MCPET shows great promise and it has some significant price as well as application advantages over the holographic lens films. I didn't properly identify this material in my first post, my bad. If I had some of this on hand I would have approached my home lighting in a completely different manner and you would not see the LED sources themselves in the fixtures I would have fabricated. (I admit to some 20-20 hind sight as well)

I just stepped away from the computer for a few minutes and grabbed my Nikon with 10-17 mm lens still in its UW housing and sat on the toilet.  I took a picture of the bathroom and the ambient light coming in from the one window is trivial relative to the light provided from the three LED fixtures in the bathroom:







I consider this more than accent light and I would add that all three fixtures use diffusing glass covers which are certainly less than efficient but do do the job. The two fixtures you see on the wall above the sink have a single red Cree along with 6 white Cree's driven by a Zitanium driver. The overhead fixture you can partially see in the mirror does not have a red LED. I didn't mess with the white balance or anything else in PhotoShop. To the naked eye, you don't see the rose tint I see in the photo but you can see some obvious red in the fixture glass covers (or what ever they are called). These three fixtures are all off the shelf incandescent fixtures that can be had from any of the large hardware chains that I modified with little effort. 


Should something like a 3 speed xitanium driver come available, I would go to the trouble of replacing these fixtures with new ones using the driver as well as Nichia High CRI 083's or 183's or possibly the 119 if they can be obtained in high CCT. Until such time, I have more than adequate lighting throughout the house with what is there now.

*EDIT* the fixture on the wall to the let of the mirror is shown below and taken from my web page. It is underexposed to illustrate the red LED as well as give a feel for the diffusion of the 7 LED's as managed by the glass shell:






If you are wearing very dark sunglasses this fixture could be viewed and considered as an accent light. (as the image apparently implies)

Well actually this image is like the fixture on the left in the photo above but it is really the fixture on the right but with the old scallop shell cover that ended up getting broken when I went to clean it one day.  The cover now on the right is a glass sconce cover that is open above and actually allows more light to escape if you compare the ceiling bounce above it compared to the left sided fixture.


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## bretti_kivi (Aug 9, 2010)

I was thinking about our lounge today; it's long and narrow and I think I'm going to try something with 6 or 7 XP-Gs in neutral around 20cms / 8" from the roof with 15 degree optics. That should give a long, dissipated beam across the ceiling, delivering the low level light that I want during the evening. Repeat for two room halves and away we go. Sketchup has at least given me an idea on this one and even if I have to push 1A through the crees, it will be a lot brighter than the present halogens - and with the size of the ceiling, it should also be a really nice, soft lightsource.

Bret


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## doctaq (Aug 10, 2010)

my first experiment with led lighting has come in the form of those cheapo led bulbs that can be had on ebay for 6 dollars shipped. it is cheap and easily reversible , i tried 3 different diffusion methods for recessed lighting in the ceiling. first off (and ugliest) is a plastic bag cut into a square and covers the socket like we normally see for fluorescent lighting at work. i took the optic off for all of these. this method could probably be done better and equally ghetto with a milk jug side. this method provided the greatest light spread with the least overall light. next i tried covering just the bulb with a plastic bag on the front, this was still very much a point source of light. next which i think is the most promising is a ping pong ball cut in half, i ended up cutting a little too much and had to push the ping pong ball dome into the bulb further than i wanted. i felt like if i could have just illuminated the ping pong ball externally (i will try this tomorrow) it would work like a small incan

mcgizmo, i am thinking about retrofitting my bathroom lighting as well, what do you do to protect the leds and driver from steam from showering?


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## jashhash (Aug 11, 2010)

I'm so glad to hear that those are underexposed images. I think my problem was just low CRI due to the 7000k XP-G's that I was using. Also I think my problem was that I didn't have proper light diffusion to bring up ambient light levels.


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## McGizmo (Aug 11, 2010)

doctaq,
I didn't do anything specific regarding the humidity. I would assume that the warmer than ambient conditions of the LED and likely Xitanium would reduce the likelihood of condensation but it's an assumption.


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## doctaq (Aug 11, 2010)

i fitted up another light yesterday, there are diffused glass domes over the stairs in my house, and the way i chose to draw eletricity is to take apart a cfl base and use that , i connected that up to two 1 led drivers from dx and connected them up to a couple of xpe, the result is plenty bright but there is a moderate shadow within the bulb that i think is coming from the socket and broken cfl base. im still just trying to keep with the reversibility of this.


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## McGizmo (Aug 11, 2010)

I rarely get back to our house in Berkeley where my wife spends most of her time but I was back for a visit a few months ago. The bathroom has a single recessed fluorescent fixture and the cold and moisture render that fixture near useless except in the warm summer months. My wife asked me to deal with it during my visit and I brought along two Xitanium drivers as well as 4 Cree strips (5 white & 1 red XRE). I mounted the 4 strips on the metal ballast cover using it as their heat sink and mounted the Xitanium's under this cover. The diffusing sheet of plastic that flushed off the fixture was viable with the LED sources as well and the improvement was very obvious switching to the LEDs.

The old and large fluorescent fixtures are an easy host for a LED modification but the smaller incan fixtures are not so friendly.


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## doctaq (Aug 11, 2010)

thats exactly what i was thinking, fluorescent fixtures already take up a fair amount of room, and the bay lighting that cree has looks to fit easily where fluorescent is currently installed.


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