Luminance Within Lunar Permanently Shadowed Regions

Exploration of the lunar poles is accelerating as multiple missions target these regions, with growing interest in studying the environment within permanently shadowed regions (PSRs)—areas at the poles that never receive direct sunlight. To prepare for these exploration activities within PSRs, we determined radiance levels in PSRs of various sizes and derived a conversion factor from ShadowCam radiance units to luminance, which is more suitable for evaluating human factors, as luminance accounts for the wavelength range to which humans are sensitive. Notably, during lunar summer, many PSRs reach luminance levels comparable to those of well-lit buildings for several Earth days each month, while peak winter lighting is typically up to six times dimmer, except in regions where regional shadows predominate and further decrease illumination. As a result, we do not expect artificial light to be needed for missions visiting PSRs during the summer peak lighting period, except for close inspection of samples. In contrast, in winter, diminished ambient lighting may require supplemental illumination for many tasks.