Integrating spheres are widely used to measure the total light output (radiant or luminous flux) of light sources such as lamps, luminaires and LEDs, but few (if any) come calibrated for measuring the output in the ultraviolet (UV) part of the electromagnetic spectrum below 350 nm. This has presented those working with specialist UV LEDs operating in the UVC (200–280 nm), UVB (280–315 nm) and UVA (315–400 nm) bands with something of a problem. The new Labsphere UV LED Flux Spectroradiometer available from Pro-Lite comes calibrated to NIST standards from 200 nm to 980 nm. It is purpose designed for measuring the spectral radiant flux in Watts of UV-VIS-NIR LEDs. It combines a compact integrating sphere for total hemispheric collection of the emitted light with a fast array spectrometer with an advanced stray light correction algorithm for accurate readings in the UV. Each system is supplied with a NIST-traceable spectral flux standard. The system can be configured with a temperature-controlled sample holder for studying the variation of light output as a function of temperature. LIV sweeps may also be performed to investigate the full gamut of electrical and optical characteristics of the LED under test. For visible wavelength LEDs, the spectroradiometer will of course report photometric and colorimetric values (lumens, CCT, CRI etc.).