How does illumination or light source affect optimization?

ANSWER:

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.