The OL UV-40 consists of a stable, 30-watt deuterium lamp with an ultraviolet transmitting suprasil window. The lamp is calibrated for spectral irradiance over the wavelength range of 200 nm to 400 nm. The OL UV-40 serves as a convenient, accurate standard for calibrating UV radiometers and spectroradiometers, or it can be used as a known source of spectral irradiance in various UV exposure tests. The deuterium lamp is especially suited for use as an ultraviolet standard since it emits a line-free continuum in the 200 to 400 nm region. Emission is strongest at 200nm, where most instrument sensitivities are low, and weakest in the visible and infrared (which reduces stray-light problems). At 250 nm, the calibrated irradiance value for the OL UV-40 is approximately 5 times greater than the 1000-watt tungsten lamp standards of spectral irradiance. Spectral irradiance values are reported in tabular form every 10 nm from 200 to 400 nm. Typical spectral irradiance curves for the OL UV-40 and 1000 W tungsten lamp standards are shown for comparison.