Ceri
The voltage drop across the LED is about 2v so you want a resistor to drop 22v. They pull about 25mA or 25/1000 A. R=V/I so R= 22000/25 = 880 ohms. I use a 1K resistor in series with a superbright red LED in microCHIP and it works fine. If you send me an SAE together with a 50p coin Ill get one of my students to make one up for you.
Rob
Address:
R H Jones, Product Design Dept, Denbigh High School, Ruthin Rd, Denbigh, LL16 3EX