How should a PCMS board operate under varying light conditions?

A Portable Changeable Message Sign (PCMS) board is designed to provide clear and legible messages to drivers, regardless of the time of day or weather conditions. Operating under varying light conditions is crucial for ensuring that the message remains visible and easily readable. When light conditions change, such as when it becomes darker at night, the brightness of the PCMS board should automatically dim to maintain legibility without causing glare or distractions to drivers.

This adaptive brightness feature helps in maintaining the effectiveness of the signage while also ensuring compliance with safety regulations. It allows the signs to be prominently displayed in bright daylight while adjusting appropriately for lower light levels to avoid overwhelming any oncoming traffic or pedestrians.

The other options do not address the need for adaptability in visibility based on environmental conditions. For example, the idea that the sign should remain the same brightness does not account for safety concerns that could arise due to varying ambient light, and turning the sign off completely at night would eliminate its purpose of conveying important information. A manual brightness adjustment could lead to inconsistencies and requires frequent user intervention, which may not always be practical or efficient.