This is a valid but difficult jewelry-lighting problem: the ring and the hand often need different light.

Diamonds usually need hard, directional specular light to show sparkle/fire, while skin looks better with softer, flatter light. Because those lighting needs conflict, the most practical solution is often to shoot two exposures or two lighting setups and composite them in post.

Good options:

• Use controlled lighting in a studio-like setup.
• Add flags/shades to keep light off certain areas.
• Light the ring with more directional light and the hand with softer light.
• Bracket exposures / use an HDR-style blend so you keep detail in both bright and dark areas.

For an already-shot image, a gamma/curves adjustment can help brighten the darker hand tones while being gentler on the highlights than a simple overall exposure increase.

Key point: jewelry photography usually depends on contrast and directionality, not flat light. If you try to light everything evenly in one shot, the diamond may lose sparkle or the skin may go dark. Separate lighting control—or compositing—is often the best answer.