The answer to 'landscape lighting yellowing' is that this is a common issue caused by a few different factors. The most common cause is exposure to UV rays from the sun, which can cause the plastic or metal components of the lighting fixtures to degrade and turn yellow over time. Another potential cause is the buildup of dirt, debris, or oxidation on the fixtures.
To fix yellowing landscape lighting, you can try cleaning the fixtures with a mild soap and water solution. If the yellowing is more severe, you may need to replace the affected components or the entire fixture. In some cases, upgrading to LED lighting can also help prevent future yellowing, as LED bulbs produce less heat and UV radiation than traditional incandescent or halogen lights.