Stumped on LED testing

[steveb]

I have some 3 Watt/420nm LED's from Shenzhen Weili Optical that are rated at
If 700mA DC forward current
If 1000mA Peak forward current
with Vf min 3.4V max 4.2V at If=700mA
3000mW Power dissipation
5V Vr (reverse voltage)

At If = 700 mA
50% power angle = 120 degrees
Luminous Intensity = min 10lm max 15lm
Chromaticity = min 415nm max 420nm

So I'm testing LED's this evening - I have a 3V/700mA wall wart. Just attaching each LED individually.

This one:
Enercell 3V/700mA Regulated AC Adapter : AC Adapters | RadioShack.com


I noticed with these LED's if I just hook them up they light but are dim compared to a Cree XRE royal blue. Now some of that is obviously due to wave length and my eye's ability to perceive it, efficiency, etc... But if I put a 50 Ohm resistor in parallel with the 420nm LED it gets brighter.

I'm sure there is a good explanation for this but I don't know what it is...
When I try to measure current through the LED by itself I get 0 zilch nodda (amp meter in series w/LED). If I measure the current going through the LED with the resistor in parallel I get 200mA.

Other weird thing is the LED actually has two chips inside the lens - I'm thinking two of their 350mA/1Watt LED's in parallel internally?...

So whats up?

 

[thewackyreefer]

I think the RC image is scaring people away. :crossedlips:

 

[steveb]

I think the RC image is scaring people away. :crossedlips:

?? I don't understand.

Never mind stupid cut and paste.....

I had posted on my local board was cutting and pasting to a couple more and well sorry about that - It didn't show up on my browser originally.

 

[CJO]

A few things are weird or don't make sense. How could you not get a reading if you have your mulitimeter connected in series and the LED is lit? They are not as bright as the LEDs because they are not as efficient. I'm surprised that they are lighting at all with a 3V power supply. It's definitely weird that you are getting a brighter light with a resistor in parallel. Sounds like you may have an issue with your power supply. Can you try a 5V one?

CJ

 

[steveb]

I know I dont understand why the meter reads 0 - I will also take some pics of the test rig with meter reading 0, the led w/out resister and the led w/reistor later this evening after my daughters softball practice. I will see if I can find a 5 or 6 volt power supply or I will rig up a couple of batteries and test.

 

[steveb]

pictures

http://s1015.photobucket.com/albums/af278/baringcs/LED Build/

 

[steveb]

I just hacked up a 9v/600mA wall wart and put a 100 ohm resistance in series w/the LED and it is significantly brighter.

I'm reading 700 mA inline and a 3.4v drop across the led. So I guess the issue was with the original power supply.

 

[Troylee]

Link don't work...

 

[steveb]

http://s1015.photobucket.com/albums/af278/baringcs/LED Build/

"h t t p : //s1015.photobucket.com/albums/af278/baringcs/LED%20Build/"

thats wierd its munging the url when I paste it in...

 

[Hahnmeister]

So what do you think of the output and color of those Shenzhen Weili Optical Actinics? Did you find a place that sells them for less than $25 a pop?

 

[CJO]

Wow, $25 each? Based on the specs, I would much rather go with Crees!

CJ

 

[Hahnmeister]

Wow, $25 each? Based on the specs, I would much rather go with Crees!

CJ

Cree doesn't make 420's.

 

[snoopie]

Im sure he knows this. Hes saying he would rather use Cree's over those 25 a pop... I sure would too... My XR-E Royal Blue Cree's do just fine.

 

[Troylee]

Links still broke... Try putting the image code here with the pics... Post them in the thread...

 

[steveb]

It ended up being the 3v power supply

I have no idea why I cant get the image code to post (its an ablum on photbucket) but if you cut and paste the URL you can see what I was talking about.

http://s1015.photobucket.com/albums/af278/baringcs/LED%20Build/

 

[Hahnmeister]

So where did you get them from anyways? Im looking myself.