What I look for in a theme is:

    1. Being easy on the eyes.
    2. Easy distinction between different keywords etc.
    3. Good contrast.

The best light theme I've seen so far is Selenized for VSCodium [1] and for VS Code [2]. There's a Selenized light for JetBrains IDEs too. [3]

[1] https://open-vsx.org/extension/santoso-wijaya/helios-selene

[2] https://marketplace.visualstudio.com/items?itemName=santoso-...

[3] https://plugins.jetbrains.com/plugin/23800-selenized-theme