am using Arduino output pin to send 5v to it through a 1K resistor. As far as i can tell what is realy happening is that is is dropping 2.44v (2.56v measured across 1K resistor and subtracted out of 5v) and is still able to trigger the Triac with a current of only 2.44ma (calculated with ohms law)??
the origional post said teh device is the MOC3010M
the data sheets lists Ift for this as 15mA with a maximum of 60mA
the Application Notes sheet : https://www.fairchildsemi.com/application-notes/AN/AN-3003.pdf
Basic Electrical Description
The AlGaAs LED has a nominal 1.3 V forward drop at
10 mA and a reverse breakdown voltage greater than 3 V.
The maximum current to be passed through the LED is
and list the MOCxx10x as 15mA
I would offer that an LED will have output degradation over the life of the unit. so the initial LED output will far exceed the ratings, but after x hours, the degradation will reduce the output. so your initial testing will prove proper operation, on the bench, with high level control of temperature and power, with a new LED that has had near zero burn-in time.
the manufacturer has to allow that some LED's will outshine others in any batch while also allowing that some receivers will be more sensitive. conversely, the worst LED of the batch coupled with the worst receiver of the batch will or should still work.
since we often speculate on these things, the production line for both devices and raw materials controls and manufacturing tolerances, etc, etc may have been delivering a superior product.
more speculation is that they may have made a huge lot of the xx23 with their 5mA threshold and since they fit the specification for every one above that, just sold the better product with a different label.
more speculation is that the LED is a POC and will fade sooner.
the app notes list 1.5v for the voltage of the LED
my take is that the manufacturer offers a minimum. best to meet that.
they do offer that going past that may degrade the LED prematurely,so there is no need to drive it any harder.
if you want to run it at a lower power, that is your choice. if you are making a board, I would offer that couple of vias, placed on either side of the resistor would allow for future modification.