Shader: get nearest point light's color, direction and general custom lighting questions

Hello,

in a Unity3D CG shader I would like to access the nearest point light's color and direction and output a computed color as the shaded object's color in my custom lighting function. (The custom lighting function is run after the surf function which I deduced from the out parameter in the surf function and the in parameter in the light function.)

My scene has several point lights and 1 directional light.

What are the required variables names? According to https://docs.unity3d.com/Manual/SL-UnityShaderVariables.html it is _LightColor0 ? And the lightDir parameter? Which direction are the *x*Dir parameters from to?

What I want to achieve is having a sphere around a point light be colored by the color of the point light, accounting for view direction (ie. plasticity of sphere). The sphere and the light is a firework particle. The sphere's normals are pointing from the center outside, parallel to the point light direction. Unity3D's built-in shader don't color the sphere probably because of that very reason of the sphere's normals. Inverting the sphere's normals occludes the point light.

Here's my current shader code:

 Shader "Custom/Firework" {
     Properties {
         _Transparency ("Transparency", Range(0,1)) = 0.5
     }
     SubShader {
         Tags { "RenderType"="Transparent" "LightMode"="ForwardBase" }
         LOD 200
         
         CGPROGRAM
         #pragma surface surf InnerLight
 
         // Use shader model 3.0 target, to get nicer looking lighting
         #pragma target 3.0
 
         struct Input {
             float2 uv_MainTex;
         };
 
         float _Transparency;
 
         void surf (Input IN, inout SurfaceOutput o) {
             o.Alpha = _Transparency;
         }
 
         half4 LightingInnerLight (SurfaceOutput s, half3 lightDir, half3 viewDir, half atten) {
             half4 c;
             c.rgb = dot(lightDir, viewDir) * atten * _LightColor0.rgb;
             c.a = s.Alpha;
             return c;
         }
         ENDCG
     }
     FallBack "Diffuse"
 }