LED Resistor value

This has been puzzling me...
Problem is this is how I did my calc...

Supply voltage - 48v
LED voltage - unknown due to buying stuff of ebay - but it was an ultrbright blue LED - similar ones have voltages around 4.5v

LED Current - christ knows - all the formulas use 20mA so I chose that

This works out to
Resistance = (48 - 4.5)/0.02
R = 2175 ohms

Now I posted that on this forum and somebody suggested I put in a 10k resistor....
The 10K resistor I put in was actually 8.8k (it was the only one I had around - it was supposed to be 10k but it was an old with with a big tolerance)
I did that and the voltage after the resistor and just before the LED comes to 3.0v
The LED shines a beautiful nice bright blue but...

Anybody explain exactly what is going on....

20mA? Not a good idea. That's the maximum current of most LEDs. Instead, I use 10mA or less as a "general purpose" approximation.

The reason your LED still works even with a resistor larger than you calculated is because the LED will simply draw less current with a larger series resistance. That's how series resistance can be used to control brightness.

As it stands, your LED is drawing about 5mA through the 8800-ohm resistor. If it's bright enough, good. If you want it brighter, you could halve the value of the resistor to give about 10mA through the LED.

[quote author="NewYorkDave"]20mA? Not a good idea. That's the maximum current of most LEDs. Instead, I use 10mA or less as a "general purpose" approximation.

The reason your LED still works even with a resistor larger than you calculated is because the LED will simply draw less current with a larger series resistance. That's how series resistance can be used to control brightness.

As it stands, your LED is drawing about 5mA through the 8800-ohm resistor. If it's bright enough, good. If you want it brighter, you could halve the value of the resistor to give about 10mA through the LED.[/quote]
Dave - great reply
I understood it - without having to reread it.
To be quite honest if it got any brighter I would have to wear shades - (christ I just turned that into a Huey Lewis moment)