How do I interpret an RGB LED max amperage given as a range e.g. 30mA-70mA?

Question

I have some LED's I got in a mixed package and the RGB LEDs instead of a single max amperage just list a range. One example is I have a common cathode RGB LED with ratings listed as 1.9-3.4v and 30mA-75mA. I've been interpreting the V range as the lowest forward V of the red to the max Vf of the green and blue elements.

Should I assume that like with the Vf the red element likely has the lower 30mA rating while green and blue have the 75mA rating, or do I assume that 30mA is the lower end of the functional range of the all 3 elements and 75mA is the max? Nothing burns out when running I run it briefly at 60mA to all colors and no issues.

Mostly I'm wondering what the standard practice is for interpreting these values when they are listed this way.

Thanks in advance.

Edit/New info Based on a great link from anrieff I've tried playing around some with the bulb in question. At below a total draw of 30mA the color balance of the bulb starts to shift from a cool white to the green. This brings up another issue, since the draw at 30mA would be 10mA per color element, does that mean the upper 70mA limit should be treated as a total instead of an upper limit per color element. i.e. ~23mA per color element for a total of 70mA instead of the 70mA per color I was originally thinking?

Answer 1

Without seeing the datasheet, it's not possible to confidently give a single reason, but here are a few possibilities:

• Each color within the RGB package almost certainly have different \$V_f\$ and \$I\$ ratings. The rating you are looking at may just be trying to encompass these values, as you have already assumed.
• It's possible that the current ratings are based on duty cycle. Many LED datasheets will provide a constant-current value (e.g. 20mA) as well as various ratings based on lower duty cycles (e.g. 50mA at 50%).

You'll need to find the datasheet or ask the manufacturer to be sure.

Answer 2

Note the current derating with rising ambient ( such as local self-heating) depends on the package and board heatsink.

I be correct to interpret the below ΔT/ΔW as (100-25'C)/20mA*3.2V= 1.17'C/mW junction temp rise above per LED for 3 LEDs to be 390'C/W rise.

The RGB LEDs that give an "Absolute Maximum" current spec usually have fine print to indicate the conditions like 10% duty cycle 2KHz or 0.1 ms. These devices may be limited by the wirebond whisker wire size that could be smaller for Red ( as they have lower Rs in the LED and lower Vf) thus the lower current for Red , I think is fusing considerations of the gold wirebond.

But overall it is the thermal resistance and power dissipation that you must pay attentionto including the need for a copper "common node" ( * ) heat radiator on the PCB. ~1 sqin/W if SMD.
(*) either Common Anode or Common Cathode

e.g.

never operate near the ABS MAX. You can measure junction temps using pulse Vf with 1~100% If due to NTC temp coefficient with pulse low If cycles, if you care about junction temps.