Help requested on powering unusual LED

I recently got a Luxeon V (I believe) LXHL-LRD5 bin T5SY dental blue LED. Being retired and with little cash flow now I am going to try the infamous 'self-dental' plan so I've gotten this LED to cure some dental stuff. Based on the bin code for this LED the 'S' is the Vf so it's listed as 5.91v to 6.39v. Since I'm still not real clear on how to drive an LED safely I'm asking for ideas on powering this LED. Based on the Vf I'm thinking I could direct drive it with two CR123's which are normally 3 volt or up to around 3.2 fresh out of the box. Would it be safe to do this or would the current drawn by the LED need to be limited with a circuit? I don't really care if this LED has a shortened life by exceeding it's limits a little bit as I won't be using it a lot but I just don't want to blow it up (very expensive Star). Any thoughts, help, suggestions much appreciated.

matrixshaman said:

I recently got a Luxeon V (I believe) LXHL-LRD5 bin T5SY dental blue LED. Being retired and with little cash flow now I am going to try the infamous 'self-dental' plan so I've gotten this LED to cure some dental stuff. Based on the bin code for this LED the 'S' is the Vf so it's listed as 5.91v to 6.39v. Since I'm still not real clear on how to drive an LED safely I'm asking for ideas on powering this LED. Based on the Vf I'm thinking I could direct drive it with two CR123's which are normally 3 volt or up to around 3.2 fresh out of the box. Would it be safe to do this or would the current drawn by the LED need to be limited with a circuit? I don't really care if this LED has a shortened life by exceeding it's limits a little bit as I won't be using it a lot but I just don't want to blow it up (very expensive Star). Any thoughts, help, suggestions much appreciated.

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While I've only had experience with Lux1 and 3s I find unless getting every last lumen is paramount, wiring a resistor in circuit with your batteries is the cheapest solution that protects your LED.
With an expensive LED like the Lux5, I'd be even less inclined to run it DD.
The correct resistor will convert the extra power into heat, and will thus reduce your runtime a bit.
I believe a one ohm resistor of one watt or greater rating should deliver 6.3v/700ma from 6.5V, but I may be way off.
I'd strongly advise you to check with someone smarter than me, and confirm the output with a multimeter before you consider hooking it up to your LED.
From memory 700ma is the correct Vf for dental luxeons, you'll probably want to check the specsheet for that too.
Current regulation circuits provide flat output and can have other features such as dimming, but are much more expensive and probably not needed here.

Thanks for the help and ideas - thought I left this reply earlier but it seems to have gone missing. I've got a MadMax 750 but IIRC I think that would be too low voltage output for this. I also found a LM7808 voltage regulator that I'm looking at - normally made to limit output to 8 volts but if I feed it 6 volts or so I think it will put out about 6 volts and the max current it will output is still limited to 1.5 amps I believe. May be only just a little safer than direct drive. The current you mentioned sounds about right - a resistor in that range may just be the simplest way to get this going. I also found a big old power supply that has 0-40 Volts D.C with 0-1 Amp - both adjustable full range. It certainly won't be portable (probably 30 pounds) but it may work.

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Thanks for reminding me about that. I found an old power supply I built from scratch with a LM337 adjustable regulator. I set it for 6.0 volts, put an 8 ohm resistor in series and checked outputs with the meter. Looked about right so I lit up the LED and it's a nice bright blue and didn't get warm on the initial test. Voltage dropped to around 5.40v while it was lit up. I haven't looked at a lot of colored Luxeons but it was interesting to see this one has no yellow in the middle but rather what looks like little metallic strips under the dome.