How many lamps may be at different levels of intensity for a Portable Changeable Message Sign to still be considered acceptable?

The acceptable number of lamps at different levels of intensity for a Portable Changeable Message Sign is two. This means that the sign must be able to display at least two different intensities for the lamps used. Having multiple levels of intensity allows for better visibility and adaptability to various environmental conditions, such as daylight or night-time usage.

This capability enhances the effectiveness of the sign in conveying important information to drivers, making it crucial in traffic management scenarios. The use of two standard intensity levels ensures that messages can be seen clearly under different conditions and helps maintain safety on the road.