Adjusting emissive intensity at runtime

For High Definition Render Pipeline (HDRP) non-Shader Graph shaders, such as the Lit, Unlit, and Decal shaders, changing the _EmissiveIntensity property does not have any effect at runtime. This is because _EmissiveIntensity is not an independent property. The shader only uses _EmissiveIntensity to serialize the property in the UI and stores the final result in the _EmissiveColor property. To edit the intensity of emissive materials, set the _EmissiveColor and multiply it by the intensity you want.

using UnityEngine;

public class EditEmissiveIntensityExample : MonoBehaviour
{
    public GameObject m_EmissiveObject;

    void Start()
    {
        float emissiveIntensity = 10;
        Color emissiveColor = Color.green;
        m_EmissiveObject.GetComponent<Renderer>().material.SetColor("_EmissiveColor", emissiveColor * emissiveIntensity);
    }
}