***NEED SOME TECHNICAL HELP***

[rdlan026]

Hi everyone,

Here's my question and was hoping someone can help. I'm trying to put together an lighting fixture with 20 LEDs and need about 30 lumens from each LED.

Is it better to go with a Nichia thats 30 lumens at 150ma or a Cree with about 70 lumens at 350 ma and underdrive it to 150ma to achieve the same brightness.

I presumably like to go with the Nichia because its less expensive and would not need a resistor.

Can some help me and explain the difference between my two options and which is better or more efficient?

Thanks...

 

[csshih]

are you talking about overdriving nichia 5mm LEDs and underdriving Cree Power LEDs?

I'm not sure it's ok to overdrive the nichias that much.. they'll probably turn a nasty blue.

nichias not need a resistor?
what are you powering them with?

also, just wondering.. why don't you just drive a few crees at high current?

 

[Marduke]

You could get a better color, and get away with using as few as 3 Cree's (4+ would be more efficient)

 

[bshanahan14rulz]

I'd say underdrive some cree high-powers, maybe some cheap xr-c low bins that will still give you plenty of light. You will want something to limit current and account for dirty source voltage. Are you trying to make Audi-esque DRLs for a car?

 

[rdlan026]

I'm trying to put together a fixture with about 20 LED's and 30 lumens each and need a small footprint LED like the Cree XP-E.

The XP-E is 70 lumens at 350mA while the
Nichia is 30 lumens at 150mA.

If I go with the XP-E, I would have to under drive to about 150mA to achieve 30 lumens.

My question is that is it okay if I run the Nichia at 350mA or is it necessary to under drive LED's to guarantee lifetime and color.

I would presumably like to go with the Nichia because its much less expensive. Thanks for your help everyone!

 

[gswitter]

Which Nichia, specifically? They make many different LEDs.

You mention not wanting to use a resistor. Are you planning to run all 20 in series? What are you using to limit the current?

 

[Marduke]

XP-E is a lot more than 70lms at 350mA. Q5 bin XP-E does 107-114lms.

It might help if you said what you're trying to build. Why does each led HAVE to emit ~30lms? Why not use less led's to produce the same brightness?

 

[bshanahan14rulz]

It is a bad idea to run high-power LEDs off of an unregulated source.
Maybe some more details about the lighting fixture could help people make suggestions. Things like what power source do we have to work with, space issues, lighting requirements (used for illumination or marker?)

I promise, I won't take your idea ;-)

Generally speaking, though, it is safer to run LEDs under spec'd current than over. xp-c perhaps might be cheaper and still be more than you need, btw. Same form factor as xp-e. Just a warning, xp-e are very very small. get out a ruler and think that these LED packages are about 3x3mm.