Final answer:
Devices like a photo-electric device and a stack switch can be used to control outdoor lighting based on natural light levels.
Step-by-step explanation:
Devices like a photo-electric device can be used to control outdoor lighting based on natural light levels. They work by measuring the amount of ambient light and triggering the outdoor lighting when the natural light levels drop below a certain threshold.
A stack switch, on the other hand, is a type of switch that allows for multiple control switches to be stacked together. While it can be used for controlling outdoor lighting, it does not directly monitor natural light levels.
Therefore, the correct answer is d. either a stack switch or a photo-electric device. Both types of devices can be used, but the photo-electric device is specifically designed for measuring and responding to natural light levels.