Using rear fog lights in clear daylight or tunnels will:

Using rear fog lights in clear daylight or tunnels can dazzle other drivers. Rear fog lights are designed to be used in conditions of poor visibility, such as fog, heavy rain, or snow, where their bright light helps distinguish your vehicle from surrounding traffic. When used in clear conditions, this brightness can reflect off surfaces and potentially blind drivers in close proximity, creating a hazard.

In contrast, the other options do not accurately reflect the purpose or effects of rear fog lights. For example, they are not intended to improve visibility for the driver using them, nor do they aid in identifying the vehicle in clear conditions; rather, they might confuse other road users. Additionally, using rear fog lights is not about reducing glare but can actually increase it for other drivers when misused. Therefore, it is crucial for drivers to use rear fog lights appropriately to maintain safety on the road.