I don't think UV plays an important part of photosynthesis for plants. But I was recently shown to be wrong about UV and FBT's, so I'm certainly not saying that as gospel.

However it's not something that will be immediately disastrous. You'll see if the plants are suffering. Then you'll just have to decide if it's the lack of light, or the "rain" leaching the nutrients from their planting medium or something else entirely.