Several factors could cause a Unity HDRP spotlight to not work properly:
Improper Layer and Culling Mask Configuration: If the layers are not correctly set, or if the culling mask of the light is excluding certain objects, this can prevent the spotlight from illuminating the scene as expected.
Lighting Settings Misconfiguration: Incorrect settings in the HDRP asset or within the Volume settings for the scene can lead to lights not functioning correctly. These settings include intensity, range, color, and mode of the spotlight.
Shader Issues: Certain shaders may not be compatible with HDRP or might be incorrectly configured, resulting in lights not affecting materials as expected.
Graphics API Compatibility: If the Graphics API used is not fully compatible with HDRP or is misconfigured, lighting can fail to render correctly.
Scene View vs Game View: Sometimes, the spotlight may appear to not work in the Scene view but works in the Game view due to the Scene view's specific rendering settings.
Max Visible Lights Exceeded: In HDRP, there's a limit to how many pixel lights can be rendered at once. If the maximum has been reached, additional spotlights may not work.
Render Pipeline Asset Configuration: The HDRP asset itself needs to be correctly configured and assigned to the project's graphics settings. If it's not, HDRP features may not work.
Version Compatibility Issues: If you've upgraded Unity or HDRP versions recently, there could be issues with version compatibility affecting lighting.
To resolve spotlight issues in Unity's HDRP, follow these steps:
Check Layers and Culling Mask: Ensure that your spotlight and the objects it's meant to illuminate are on the correct layers and that the culling mask includes those layers.
Review Lighting Settings: Double-check the light's properties, such as intensity, color, range, and mode, to make sure they're set appropriately for your scene.
Verify Shader Compatibility: Confirm that the materials affected by the spotlight are using HDRP-compatible shaders.
Graphics API Check: Make sure you're using a compatible Graphics API for HDRP and consider switching to another one (such as from DirectX to Vulkan) as a test.
Toggle Views: If the issue is with the Scene view, toggle between Scene and Game view to determine if the problem persists in actual gameplay.
Adjust Light Limits: If too many pixel lights are in the scene, increase the maximum allowed pixel lights in the HDRP settings or reduce the number of active lights.
Configure HDRP Asset: Verify that the HDRP asset is correctly set up in your project's graphics settings. If necessary, create a new HDRP asset and assign it.
Check for Updates: Make sure both Unity and HDRP are updated to the latest stable versions. If you've recently upgraded, check release notes for any changes that could affect lighting.
Consult Documentation and Community: If these steps do not solve your problem, refer to Unity's official documentation and community forums for more specific solutions related to your error.