Los Alamos National Laboratories has completed the design, manufacture and calibration of a vacuum-compatible, tungsten lamp, integrating sphere. The light source has been calibrated at the National Institute of Standards and Technology and is intended for use as a calibration standard for remote sensing instrumentation. Calibration 2(sigma) uncertainty varied with wavelength from 1.21% at 400 nm and 0.73% at 900 nm, to 3.95% at 2400 nm. The inner radius of the Spectralon-coated sphere is 21.2 cm with a 7.4 cm square exit aperture. A small satellite sphere is attached to the main sphere and its output coupled through a stepper motor driven aperture. The variable aperture allows a constant radiance without effecting the color temperature output from the main sphere. The sphere's output is transmitted into a vacuum test environment through a fused silica window that is an integral part of the outer housing of the vacuum shell assembly. The atmosphere within this outer housing is composed of 240 degree(s)K nitrogen gas, provided by a custom LN2 vaporizer unit. Use of the nitrogen gas maintains the internal temperature of the sphere at a nominal 300 degree(s)K +/- 10 degree(s). The calibrated spectral range of the source is 0.4 micrometers through 2.4 micrometers . Three, color temperature matched, 20 W bulbs together with a 10 W bulb are within the main integrating sphere. Two 20 W bulbs, also color temperature matched, reside in the satellite integrating sphere. A silicon and a germanium broadband detector are situated within the inner surface of the main sphere. Their purpose is for the measurement of the internal broadband irradiance. A fiber-optic-coupled spectrometer measures the internal color temperature that is maintained by current control on the lamps. Each lamp is independently operated allowing for radiances with common color temperatures ranging from near 0.026 W/cm2/sr to about 0.1 W/cm2/sr at a wavelength of 0.9 micrometers (the location of the peak spectral radiance).