Uniform illumination from UVA LED lamps is a crucial design characteristic for a range of industries including photocatalytic applications. In this work, radiometry and the discrete ordinate method (DOM) are used to determine the ideal target surface size and working distance from a UVA LED lamp for highly uniform illumination. Horizontal incident radiation and full surface incident radiation measurements were conducted using a scanning radiometry technique. It is shown that horizontal incident and full surface incident radiation measurements show good agreement for uniformity measurements over a range of working distances, with maximum uniformity (2.6% and 3.6% standard deviation respectively) over the measured range found at 15 mm working distance. DOM simulation results showed good agreement with radiometry for power and incident radiation measurements, whilst indicating a maximum uniformity at 20 mm working distance. These results demonstrate that DOM simulations can be used as a fast, low cost, and reliable indication of surface uniformity, peak surface irradiance, and power measurements in the design of UV lamps for industrial and academic applications.