Connect the positive terminal of your battery supply to the left lead of a 1,000 ohm resistor. Connect the right lead of the resistor to the left lead of the LED. Connect the right lead of the LED to the negative terminal of the power supply.
Turn on your power supply. Raise the power supply voltage to 1 volt. Observe whether or not the LED emits light. If the LED lights, the positive end, or anode, of the LED is the lead that connects to the resistor.
Continue raising the voltage in 0.3 volt increments if the LED doesn't light. Observe if the LED lights at each 0.3 volt increment until you reach 3.0 volts or the LED begins to emit light. If the LED doesn't light at or below 3 volts, the LED lead that connects to the resistor is the negative lead, or cathode, and the positive end, or anode, of the LED is the lead that connects to the negative terminal of the battery. If the LED does light, the LED lead that connects to the resistor is the positive end of the LED and the negative end of the LED is the lead that connects to the negative terminal of the battery.