Method for operating and testing a light detection and ranging system , particularly for safety relevant applications, comprising alternating operating and testing cycles, wherein the operating cycle comprises the steps of: sending a light signal from at least one first light source to the surroundings of the light detection and ranging system ; receiving a light signal from the surroundings of the light detection and ranging system by at least one photo detector ; processing the signal of the at least one photo detector for detecting objects in the surroundings of the light detection and ranging system by a signal processing unit ; controlling, particularly synchronizing, the sending of the light signal and receiving of the light signal by a control unit ; and wherein the testing cycle comprises the steps of: sending a test light signal within the light detection and ranging system to the at least one photo detector by a second light source of a test unit ; receiving the test light signal from the second light source of the test unit by the at least one photo detector ; processing the signal of the at least one photo detector by the signal processing unit ; comparing the signal of the signal processing unit with an expected signal based on the test light signal for testing the light detection and ranging system , characterized in that the test light signal is generated by a test light signal generating unit , wherein the test light signal generating unit can generate specific test light signals with different waveforms and wavelength designed to test specific functions of the light detection and ranging system . sending a light signal from at least one first light source to the surroundings of the light detection and ranging system ; receiving a light signal from the surroundings of the light detection and ranging system by at least one photo detector ; processing the signal of the at least one photo detector for detecting objects in the surroundings of the light detection and ranging system by a signal processing unit ; controlling, particularly synchronizing, the sending of the light signal and receiving of the light signal by a control unit ; and wherein the testing cycle comprises the steps of: sending a test light signal within the light detection and ranging system to the at least one photo detector by a second light source of a test unit ; receiving the test light signal from the second light source of the test unit by the at least one photo detector ; processing the signal of the at least one photo detector by the signal processing unit ; comparing the signal of the signal processing unit with an expected signal based on the test light signal for testing the light detection and ranging system , characterized in that the test light signal is generated by a test light signal generating unit , wherein the test light signal generating unit can generate specific test light signals with different waveforms and wavelength designed to test specific functions of the light detection and ranging system . sending a test light signal within the light detection and ranging system to the at least one photo detector by a second light source of a test unit ; receiving the test light signal from the second light source of the test unit by the at least one photo detector ; processing the signal of the at least one photo detector by the signal processing unit ; comparing the signal of the signal processing unit with an expected signal based on the test light signal for testing the light detection and ranging system , characterized in that the test light signal is generated by a test light signal generating unit , wherein the test light signal generating unit can generate specific test light signals with different waveforms and wavelength designed to test specific functions of the light detection and ranging system . <EOS>