Abstract: The disclosure provides a method and apparatus for regulating an energy input of a pulsed arc plasma during a joining process by detecting first measurement signals for a first temporal response of emission light from an arc plasma in a first spectral range with a first photodiode, which has a sensitivity maximum at a first wavelength, detecting second measurement signals for a second temporal response of emission light from an arc plasma in a second spectral range, which is at least partially different from the first spectral range, with a second photodiode having a sensitivity maximum at a second wavelength that is different from the first wavelength, generating control signals by comparing the first measurement signals and the second measurement signals, and regulating an energy source, which is configured to provide energy in pulsed form for the arc plasma in accordance with the control signals.