Integrating sphere (IS) based uniform sources are a primary tool for ground based calibration, characterization and testing of flight radiometric equipment. The idea of a Lambertian field of energy is a very useful tool in radiometric testing, but this concept is being checked in many ways by newly lowered uncertainty goals. At an uncertainty goal of 2% one needs to assess carefully uniformity in addition to calibration uncertainties, as even sources with a 0.5% uniformity are now substantial proportions of uncertainty budgets. The paper explores integrating sphere design options for achieving 99.5% and better uniformity of exit port radiance and spectral irradiance created by an integrating sphere. Uniformity in broad spectrum and spectral bands are explored. We discuss mapping techniques and results as a function of observed uniformity as well as laboratory testing results customized to match with customer’s instrumentation field of view. We will also discuss recommendations with basic commercial instrumentation, we have used to validate, inspect, and improve correlation of uniformity measurements with the intended application.