Well, nobody can help you make the LEDs meet your expectations.

So just forget the expectations and use actual measurements to calculate your resistors.

 

Well, nobody can help you make the LEDs meet your expectations.

So just forget the expectations and use actual measurements to calculate your resistors.

thanks for the good advice ElectricSpidey but for now i am going to keep the laws of physics within my realm of expectations and if I encounter any future contradictions ill be sure to look for your post in my thread.

 

thanks for spitballing this with me everyone.

so its not a filtering issue. its an automotive application so im looking at 12.6 to 14.1 volts DC. specifically its a public safety project that has to function normally without the vehicle idling and just to be certain I used 3 series lithium polymer cells (12.6 volts DC) as a voltage source and got the same results.

crutschow i thought the same and thankyou for supplying the graph but these are showing a higher forward voltage under load than when tested out of the box. I could look at a data sheet for an equivalent part but these are "fake chips" from no name china manufacturer so unfortunately the numbers would be meaningless.

to those who didn't catch it before the LEDs in question are 5730 package 6000 kelvin smds. and yes there is a heat sink pad on the LED that in this case is connected to the anode. Ive designed a custom footprint and am etching PCBs by hand that are inlayed into aluminum. I'm forced to leave the fiberglass in the PCB as an insulator between the LEDs and the aluminum because of the polarity of the heat sink pads. the PCB should transfer enough heat energy (although it is thermally insulative) into the aluminum for the current design parameters to work.

no, its not a fluke manufacturing error, I have thousands of LEDs from two completely separate manufacturers and I'm pretty sure the sections of tape and real I have are from different spools. I also have LEDs from the same manufacturers in blue(FV 2.508), red (1.824) and amber (1.844). those values are tested and i should mention that all of these LED varieties are testing and operating normally at the rated 150mA with the same set up I've described, under the same conditions, with the same measurement equipment. only the white LEDs are preforming outside of my expectations.

Hi,

It sounds like if you would like to get a better correlation between what you want and what you get you probably have to order some new LEDs Get a different part number LED and see if it gets closer to what you expect and then you can be more confident about the design overall.

The temperature effects are a bit hard to deal with mathematically. The curves actually depend on the forward current itself as well as the temperature itself, so you may see a gradual straight-line decrease in forward voltage with temperature, or you may see the forward voltage fall suddenly then taper off with temperature at higher forward currents. The difference can be as much as 30mv or more, so you really have to test at several forward current levels to get the full picture. So the slope can be nearly constant over temperature or can be much more negative with temperature and then become less negative at higher temperatures with higher forward currents.

In any case, try some different LEDs see if you can get an improvement.

You also probably know that constant current drive is usually the best, and for more critical applications the forward voltage is measured and used as feedback to control power dissipation (such as with a microcontroller).

 

If you accept that the actual voltage drop across each of the three LEDs in series equals about 3.2V,

I = [12V- (3 X 3.2V)] / 30 Ohms
I = 80 mA