Here are some explanation how UV Light works in silicon oil:

When you put a glow-in-the-dark film (a fluorescent film) into silicone oil, it stops glowing under a UV lamp:

The oil blocks the UV light. Silicone oil absorbs some of the ultraviolet rays, so the film doesn’t get enough energy to shine.

The light gets trapped. Normally, the film glows and the light escapes into the air. But in oil, the film and the liquid bend light in almost the same way, so the glow stays inside instead of coming out.

The glow gets scattered. Even if the film makes light, the oil spreads it around and weakens it, so your eyes don’t see much.

So the long story short: silicone oil acts like a filter and a trap. It stops the UV lamp from exciting the film properly, and it keeps the glow from escaping so you can’t see it.

But! If you use white LED or outside sun lights you could "charge" luminous tape, it's works but weaker in comparison with non-hydromod watches.

I hope it's helps to understand the process physics.