Instrument Systems was the first company in the world to develop calibration UV-LEDs that can be traceably calibrated to radiant flux. The calibration UV-LEDs of the ACS series are available for the typically peak wavelengths of 280 nm (UVC), 305 nm (UVB) and 365 nm (UVA). The proven ACS series on LED basis now covers the complete visible and infrared to deep into the ultraviolet range. The traceability of the radiant flux is achieved due to the highly precise calibration of the spectrometer optical probes to the irradiance and integrative measurement with the goniophotometer. The extremely low measurement uncertainty (k=2) of only 4.5% (UVC), 3.5% (UVB) and 2% (UVA) is comparatively low, as in the metrologically unproblematic visible range. Calibration UV-LEDs can be used for monitoring and absolute calibration of the special UV measuring equipment such as integrating spheres of the ISP-UV series.