I have a basic circuit using a BJT common emitter which I have constructed to pulse a red LED on to use as a strobe with 1us ON time (@12V) and plenty of time to cool down (<< 1% duty cycle). The pulse is coming from an Arduino MEGA 2560.

Initially I was running it with a series resistor as it that is the way I have been taught is 100% necessary when using LED's, however I have been testing without one, and it is pulsing brighter (measuring using a photodetector) and not burning out.

Just wondering what kind of lifetime I could expect from operating a LED in a manner like this, or any other effects that I should be aware of. And also if I am correct in assuming that the internal resistance of a LED is on the order of 10 ohms?

I am 90% sure this is the datasheet for the LED.
<http://www.jaycar.com.au/products_uploaded/ZD1790%20-%20TLCR5800.pdf>

Thanks