5mm vs Luxeons for lighting

Hi Folks,

I'm thinking ahead to the day that I build some accent and under cabinet lights out of LED's. These would be low voltage powered and not from batteries so power usage is less of an issue.

Would it be better to use a few luxeons or a lot of 5mm whites? I haven't yet ordered or played with the luxeons as I'm waiting to see what happens to the price of the 1w after the 5w is available in white. I'm concerned about heat sinking and light color though. I absolutely love the white from the nichia 5mm LED's and I definitely don't want to build under cabinet lights with green lights in them!

I know that I could probably use halogen lamps for this type of project, but they are expensive too and not nearly as much fun to play with

At $18 for 10 white 5mm and a similar price for a single luxeon, the question is valid I think. I wouldn't mind spending a little more for large arrays of 5mm if I was going to get a better looking light.

What thinks you folks?

Thanks,
James

I would go with 5 or 3 mm Nichias, for a more even lighting. Maybe even wide angle ones...

Added advantage is you can put them in smaller places.

Hello James,

For starters, if you need the higher level of illumination available from the Luxeons, then go with them. On the other hand, if you want a nice low level of illumination, it's tough to beat the consistancy and color of the Nichia. I have been making 12 VDC lights, similar to what you have described for over a year now and have quite a few installations under my belt. If you go with the Nichia, 3 LED's in series with a resistor works well on 12 volts and the small amount of heat generated is no problem. With the Luxeon's, you will need a driver like the Xitanium and heat will be a consideration. I have one fixture where I have clustered 9 LED's. This fixture will get up to about 107 deg. F. Beyond 9 LED's in a fixture, I would recommend considering the Luxeon.

An under cabinet installation:



In this installation, There are 3 cluster LED's in brass fixtures mounted up underneath the cabinets as well as the same fixtures mounted in the face of the cabinets. I have a silicone disk over the LED's to soften, warm and diffuse the light. This photo was taken with the LED's as the only light source.
I would highly recommend that you consider using the Nichia 3 mm LED's, part number NSPW312BS instead of the 5 mm. The 3 mm LED's use the same die but the 312 gives you a wider beam with a more even light distribution.

For some more ideas, you can look at a funky web page I put together: Tri-CLuster LED lights

- Don

5mm Nichias are still substantially more effecient than Luxeons. If you're running off a limitied power supply (batteries), the 5mm would be better...but then again, there's not too many nuts like me that aspire to break free from the opressive thumb of the power grid

"but then again, there's not too many nuts like me that aspire to break free from the opressive thumb of the power grid"

Except around here...lets see, Ted, I think Darell isn't completely grid free but aproaching it, uhh...and some others

Well, the lights shown above are run off a 12 vold deep cycle gel battery so the grid isn't needed................. except to charge the battery occasionally..............

McGizmo, it was surfing your site that got me interested in this as a project in the first place I suppose part of why those pictures are so beautiful is where they were taken, my location can't compete with that, but still...

I suppose I need to order a few luxeons to experiment with and see just what kind of output they have and how much heat I'll have to get rid of. Reading the various sites I see that people claim that a luxeon can take the place of anywhere from 10 to 24 5mm white LED's. If it's 20 then they would be considerably cheaper, if it's 10 then they would be similar.

It seems that the voltage requirements are similar. So I could still run 3 in series with a small resister from a 12v supply. If the 5mm sink 20ma and the luxeon sinks 350 then it pulls as much power as 17 of them. So if it can really replace 20 of them then it will be more efficient. the stringing of them with resisters affects efficiency also though. If I have 7 strings of 3 5mm with a resister on each one at 21 mw used in each resister thats 147mw lost as heat. The luxeons need closer to 3 volts and at that amperage the 8.2 ohm resister necessary would sink a whopping 889mw! Just shy of a whole watt of a heater in each string...

However, since the voltage requirements are just above 3 volts it may be possible to run 4 of them in series without any resister at all, or with a very small one.

This is hard to calculate till you buy a lot of them as there seem to be a lot of variation in their forward voltage requirements. As well as their color. Also, all my calculations may be completely wrong as I'm new to the subtleties of LEDs and especially the luxeons.

As far as getting off the grid, this is a long standing dream of mine, but I'm unwilling to sacrifice my lifestyle for it. (and my family would be even more unwilling to sacrifice theirs) Where we'll be moving to next year does have it's share of hurricane related storms and the associated power outages. So I will be having some of my time off the grid whether I like it or not. I'm already planning to get a big generator with enough power to keep the AC running. That will probably cost me in the 2 to 4 thousand dollar range (obviously not something I'll be getting into right away) and a few other circuits could be run from that as well like the fridge and computers. But having lights around that are easily run for extended periods from a small bank of batteries would be ideal. This is also part of the plan for the lights I'm talking about here.

Right now I haven't decided if a centralized big battery system would be better, or smaller nicad or nimh cells built into some of these lights to run them individually. Running extra cable in older houses is a big pain and there are significant cable losses when pulling power at low voltages unless you use big cable. So the later might be better. Some simple charging circuits to float the batts all the time and kick over to battery when the power goes out.

Quick power calculation question. If I use 4 luxeons at 12v in series then they are pulling 350ma at 12v or 4.2 watts correct? So a small switching power supply that you can buy for around $3 that has a 12v @ 1 amp output (which is 12 watts?) should be able to run at least 2 strings of 4 and maybe 3 if you want to push it to the limit of it's rating. Do I understand ohms law correctly or is this horribly wrong

Thanks,
James

James,

I don't know if you have been following some of the threads on the Luxeons but I am convinced that the Luxeons need more than a simple resistive circuit. You are correct with your calculations RE: string 3 or 4 in series but the Vf varies so much from one Luxeon to the next that I think you could find some burning up while others may be below spec, current wise. I am in the process of coming up with a Luxeon addition to my line but it will entail having a Dat2zip designed, step down, constant current driver in each light fixture. My other concern is the variation in color from one Luxeon to the next. In many cases, I think the Luxeon's are over kill but in other applications, it will take a luxeon to displace a small halogen bulb.

In the absence of other ambient light or light polution, don't underestimate the power and utility of a single LED! With the advent of the Luxeon 1 W's and the soon to be available 5W's I am afraid the small, efficient Nichias may never get the attention they so well deserve. 3 Nichias in a night light will light up a whole room with enough illumination for ingress and egress.

I keep waiting for Nichia's entrant to the higher power LED's with their 10X but it seems that they are still having QC issues.......

If you decide that you need some Luxeons in your system, I would recommend that you consider a bank of 12 volt batteries in series so you have 24 VDC as well. With a Xitanium 24 volt driver, you can keep the wire size down and run some Luxeons without worry of current control.

You mentioned a small resistor. I assume you mean small in terms of resistance. Depending on the current, the resistor may be actually large physically; depending on the watts. I strongly recommend against resistive circuits for Luxeons. This isn't a flashlight application where the LED may be only on for minutes or even seconds at a time. You are in this for the long haul and will want years of 10 to 12 hours per day duty.

- DOn

I'd caution anyone attempting to run luxeons off a standard 12V switching power supply. Hook up a multimeter and check the current draw to make sure you're running to spec.

I'm doing the same thing and find that I needed to nearly double the amount of resistance I initially thought I needed. To calculate resistance, I used the well-known "resistors without tears" calculator (link found on Craig's website).

My situation is a little different from yours, but McGizmo is correct - get a Xitanium and save yourself the pain and risk of burning up those precious luxeons.

Good luck with your project!

(PS - please post pix when you're done - I'd love to see how they do as I'm working on undercabinet lighting too )

This is really terrific guys, thank you for all the info!

I checked out the Xitanium drivers website and downloaded their documents. It certainly seems like the thing to have if you're using Luxeons. My concern is the same as has already been voiced here that if they are all so different in their forward voltages it will not produce a good display either. When we're buying a small quantity of luxeons, what are our chances of getting good ones binned together? I probably wont be buying 10,000 of them like a proper industrial partner (although if I did could I turn around and sell the ones I didn't use back to people on the boards here? don't answer that, it will be months before I get to that point)

I have been trying to follow all the luxeon threads here, it takes a lot of reading! I do recall the difficulty that people have had with the current regulators at the higher current levels. But I was under the impression that was because they were trying to build something that would fit inside of a flashlight body. In this case thats not a problem so a more spread out design could be used.

I'm probably not up to designing those circuits from scratch, but I can certainly build one.

Have you spoken enough to the Xitanium folks to get a ball park on the price of those modules? If they are inexpensive then I can see them being perfect, but if they are pricy then I will at least waste the time trying to build my own current regulators...

First project will be to just wire up the 10 5mm's that I just got in the post here and see how much light I can get out of them in regular "lights on in the room" kind of applications.

Thanks again,
James

There is no simple answer to your question.

First and foremost is the ambient enviroment. Any light pollution whether from indoor lights, side lighting, TVs, and street lights will affect the amount of light you will eventually need.

For a total blackout, a single white Nichia is more than enough to light a very large area.

In most suburban areas and major cities the light pollution from all the street lights bouncing off the air polution create a "light fog" that raises the total blackout to something brighter than total darkness as compared to pitching your tent in a dark forest.

To make lighting useful it must provide enough light to overcome the ambient pollution enough to provide some constrast between the ambient and the object you are trying to light. whether you are trying to spot focus on a counter or flood a whole area like a room you must overcome the ambient or your light is doing nothing.

Take some of this into consideration.

Where McGizmo lives has less light pollution in his neighborhood, but, where I live it's a lot higher. I think for me I'd need about twice as many outdoor lights to get the same effect to light up my walkway for example.

If you are just going to build a single fixture, a resistor to current limit the LED will probably get you by especially for the Nichias.

With the Luxeons I think the LEDs are already dissipating enough heat (1W) and adding more in a dropping resistor would just compound the heat issue.

There are many as you say good step down regulator ICs that won't fit inside the guts of a flashlight that should be more than acceptable for your project being a larger physical design.

I'm working on two right now and if you would like more info you can drop me an email and I could give you more details on what I have.

It's real easy to goto any store and find the cheapest keychain white LED light for testing purposes and pick up two-five of them. Then you can test, point, move them around and see what a single white Nichia will do. Most keychain lights are driven either to specs, slightly overdriven or quite overdriven. Most fall into the category of slightly overdriven.

They also make good flashlights and emergerncy lights and if you don't have any flashlights sometimes a great place to start your flashlight collection...

BTW: The Luxeon Vf voltage like standard LEDs are a wide variance. The 1W Luxeon has a VF range of around 2.9V to 3.6V. This is true for all LEDs and constant current is the only true way to create consistant lighting.

Luxeon products have limited production or are the only sole source provider. The LEDs are "binned" and graded, but, nobody, not even the big players are getting similar binned LEDs at this time.

As Don pointed out, the Nichias have quality control on the 5mm and 3mm LEDs down pat. Getting a bag of Nichias will yield them to be consitantly the same time and time again.

Not so for Luxeon. Not at this point so, be warned that no two Luxeons are going to be the same even if they come off the same reel and are supposed to be "binned" and graded the same.

The Pea green effect is not on the color chart for white color balance based on the Kelvin color grading scheme of a hot object in a vacumn. 5000K, 5500K, 6000K.

WayneY

What would you be using if LEDs wern't an option?

If you would be using those compact halogen lights, then I'd say go with the Luxon, but if you would be using those miniature flouressent lights, then I'd have to say go with the Nichias...

As has already been said, it depends on the application.

I did some experimenting last night with 9 5mm LED's outside running from 12v with a resister and am actually very impressed.

Even with my deck lights on at 50% they were able to quite usefully light up plants and trees and other accent items. I'll play some more tonight I think I may postpone my indoor projects and build a few lights for outdoors to connect to the 12v outdoor light transformer that is already here for a few deck lights. I will need to dig up some diodes or something since that is AC. They really do give a LOT of light in the dark.

But as you say, ambient lighting makes a big difference. Inside the same array was much less impressive. It was probably bright enough under the counters, but it was too concentrated. The 3mm's should be more diffuse? I would guess that 20 or so would make a nice, but not too bright under cabinet light. I'll order some of the smaller ones and see what happens

If I am required to build electronics for each lamp and do some kind of extra heat sinking for luxeons, then I am hesitant to dive into that right now. Any price savings for the light elements would be offset by spending a lot more time in construction and money on extra parts. But I'm still going to order a couple to experiment with.

I've been running the 5mm's right on their rated current of 20ma (ok maybe 22ma when I measured it) and they do get warm, but nothing that will require any extra heat handling.

Thanks,
James

James S, I know exactly how you feel. When Don showed Wayne and myself the surroundings of his house and that of another friend's (all done up with his tri-clusters/nine-stars), I was in awe.

The LED's soft "moonlight" glow bouncing off foliage and people almost caused me to spout poetry! It may sound kinda creepy to some (it did to me at first), but that glow kinda grows nicely on you - particularly if you are with an *ahem* - special lady friend