The less intense the illumination, the more diffuse (homogeneous) it will be. An average spot size of reasonable homogeneity is about 10 cm at a 50 cm lamp distance. Two lamps improve this geometry significantly, especially for large targets. If lighting conditions are so poor that you are continually re-optimizing, try optimizing with a brighter source:

• For outdoor optimization, tilt the Spectralon panel directly towards the sun during optimization.
• For enclosed illumination of targets requiring contact measurements, we recommend ASD's High Intensity Reflectance Probe or Source Probe.
• Under low light conditions, consider using a reference panel < 99-100% white and then post-process out the difference between the white and gray reference in ViewSpec™ Pro.