Ok, for starters light as energy has three primary functions that are genrally accepted by readers, death lasers, barriers, and buffs. The main argument for lasers is that light is hot when concentrated, barriers because photon has a pushing force, and buffs because light passes on energy for growth and is permeable. Some more niche abilities are invisibility, illusions/mirages, and scrying(viewing things from far away). These work because light affects the visual field. You can get a lot of ideas for light usage from physics.
Some would say Shadow is trickier to do as it doesn't do much in the real world to draw inspiration from, but I personally see it as the freedom to be creative with it without alienating your audience, and use a character with the shadow attribute in my own story. You can use it for a lot pretty easily, like teleportation through shadows(if you really want to lean into this you can even make an entire other shadow dimension that the user travels through), cloning, item storage, using parts of the shadow as replacement skin to stop bleeding, stretching to touch physical objects too far from the user, slithering into gaps to spy, wiggling to absorb some impact damage, hindering opponents movements, illusions, the list goes on. The only things you really want to avoid with shadow is absorption, as that's pretty heavy in the darkness territory, and if you're using shadow then you want to keep the distinction clear or people will think of it as another reskinned darkness. If you're still looking fir ideas on shadow try looking into folklore and fairytale, they make good use of shadows often and may give you inspiration.