Blue LED brightness issue

I have bought the Starter Kit and am using the components to complete all the sketches in the "Getting Started with Arduino 2nd edition" book.

I just got stuck for many hours with what seemed to be at first a software problem with the last sketch (networked lamp adjusting brightness of leds based on words in a web page read by Processing sketch).

Once I ruled out the software I checked the wiring, ruled out that too until I noticed that wherever I moved the blue LED it seemed to work according to the sketch.

I went back to a very simple dimming cycle sketch and actually noticed that the blue LEDs I got are always much brighter than all the other ones.

Is this always the case, is there a problem with my LEDs or could I still be doing something wrong?

noticed that the blue LEDs I got are always much brighter than all the other ones.

Modern blue LEDs are more energy efficient than other colours of LED due to the material they are made from. So your results are no surprise.

I have 9w 6700k LED’s and 1w blue LED’s. At the lowest setting the blue are a lot brighter than the whites, I was very surprised by this. Both use the same driver type.

robsworld78: I have 9w 6700k LED's and 1w blue LED's. At the lowest setting the blue are a lot brighter than the whites, I was very surprised by this. Both use the same driver type.

Would you have some specs other than wattage ?

These are the LED's and drivers I have.

2700k http://ca.mouser.com/ProductDetail/Cree-Inc/CXA1304-0000-000C0Y840E8/?qs=T2s9liuQIJMbHN1w7IO8EA==

6500k http://ca.mouser.com/ProductDetail/Cree-Inc/CXA1304-0000-000C0Y840E8/?qs=%2fha2pyFadujmUlb3KOounNBBjzCpcdaZdakBo%252b8G2rj5n9NhB9%2fLAD595id8ipIY

Royal Blue Moonlight http://www.rapidled.com/royal-blue-moonlight-led/

Meanwell LDD-700HW driver http://ca.mouser.com/ProductDetail/Mean-Well/LDD-700HW/?qs=Nu4vD1zweAZkErv%252bUFEL7A%3D%3D

Next time we learn how to post links :P

So you have some LEDs that need 350mA constant current and some 440mA constant current LEDs. How are you powering these from a 700mA constant current driver ?

Something funny with those mouser links, no matter what I try they won't work, blame it on the forum. :)

On each of those mouser pages there's a link to the datasheet. You'll see these are actually capable of accepting up to a 1000ma and can put out more lumens than mouser page says, that's the testing current.

The moonlights I'm running them in parallel, doing that will split the current between them. I have 3 in parallel on one driver so each is getting 233ma. I'm going to wire them all on one driver because they are to bright. Only have 3 in parallel isn't the best practice either because if one was to burn out the other 2 LED's would get 350ma pushing them to there limit. When I wire all 6 they should get about 116ma each, then I have more room for burnouts. Its usually not recommended to wire them parallel.

You can not run raw LEDs in parallel, they will not shair current.

They are wired + to + to + and - to - to - then to driver? That’s how it was explained to me.

This is what I was told.

wire 2 in parallel..

Voltage adds in series.. Amps add in parallel..

Just be aware that "if" one fails open, the remaining one will get all 700mA... Most that run parallel fuse the end (1/2A fuse is probably good in this case) as a precaution on losing both in this event....

One of the gotchas of parallel LED design..

It has to be true because my LED's aren't getting 700ma.

Wiring high power LEDs in parallel is not a good idea whatsoever and there is really only one gotcha about parallel LED design: it is a BAD idea.

Also, with all that LED power and driving these closer to their max current make sure you have excellent heatsinking with fans.

It has to be true because my LED's aren't getting 700ma.

No that is not the measure of that being true. They may not be getting 700mA but do you know what they are getting? The answer is no, and you can never control what they are getting because parallel LEDs simply do not share current anywhere close to equally. The inequality will change as the LEDs age and will also change as the temperature changes. Any one who advises you to wire LEDs in parallel is a stupid idiot.

That's how it was explained to me.

Stop hanging out with morons.

lol, I don't know the person, someone on a forum. They've been hooked up for a couple months now and seem to be ok, but yeah if its wrong its wrong. So I should be getting a lower powered driver or is there a way to drop the current on one of these?

Its not always easy taking advise online because I don't know when someone is telling me something wrong especially if what they say seems to work. When I search parallel digrams on the net I get all kinds so you have to give me a pass on this one. You just saved me buying new drivers because of wrong advise. ;)

I don’t know when someone is telling me something wrong especially if what they say seems to work.

The clue here to the fact they don’t know what they are talking about are the words “seems to work”. This implies no knowledge at all but it did not immediately break so then it must be fine. Sadly this attitude is all too prevalent on the internet and results in the unremitting crap that is the instructables site.

You just saved me buying new drivers because of wrong advise.

Well it was more of the LEDs because the drivers will protect themselves. Because they are constant current then they will only supply that current even in the face of a short circuit.

So I should be getting a lower powered driver

Yes.

Grumpy_Mike:
Well it was more of the LEDs because the drivers will protect themselves. Because they are constant current then they will only supply that current even in the face of a short circuit.

I was talking about a different thread.

Not only should you be getting lower powered drivers, but also you may want to watch the LEDs as they likely already have suffered damage. The damage to an LED due to over current is not necessarily immediately visible.

When an LED receives more current that is specified in the spec sheet it will not be able to dissipate the heat and the die will get too hot. That does not need to immediately result in a burned out LED but it's lifetime will be a lot less than specified.

That's also the reason that you need to make sure to have very good cooling in place when driving LEDs close to teir Max current.