Design allows any color LED to be tested. No need to worry about choosing the proper resistor for protect the LED. simply snap the tester n a 9V battery and start testing. Includes spring-loaded contact block to hold wired LEDs.WARNING: This product can expose you to chemicals including LEAD, which is known to the State of California to cause cancer and birth defects or other reproductive harm. For more information go to www.P65Warnings.ca.gov