The new calibration LEDs in the ACS-530 series from Instrument Systems GmbH enable users to check optical instruments easily and reliably. Calibrated using traceable standards for luminous flux and intensity, the LEDs offer reproducible and stable optical output power for reliable measurements. They feature photometric stability of 0.1% and are housed in a casing with low thermal conductivity together with a thermoelectric cooling element to eliminate sensitivity to external temperature fluctuations, and a temperature sensor. The LEDs are available in red, green, blue and white. They are suitable for checking results for dominant wavelength, color coordinates and color temperature.