Toon Shader produces weird defect? (pic included)

Questions & Answers
1

The following toon shader makes a weird defect, like there is a second light in the scene.

Shader "Custom/Rim_Light" {
	Properties {
		_MainTex ("Base (RGB)", 2D) = "white" {}
		_LightBright ("Bright", Range(0, 1)) = 0.7
		_LightDark ("Dark", Range(0, 1)) = 0.3
	}
	SubShader {
		Tags { "RenderType"="Opaque" }
		LOD 200
		
		CGPROGRAM
		#pragma surface surf Custom

		sampler2D _MainTex;
		float _LightBright;
		float _LightDark;

		struct Input {
			float2 uv_MainTex;
		};
		
		half4 LightingCustom (SurfaceOutput s, half3 LightDir, half atten) {
				half NdotL = dot (s.Normal, LightDir);
				half c;
				if ((NdotL) > 0.7){
					c = _LightBright;
				}
				else {
					c = _LightDark;
				}
				return c;
		 }

		void surf (Input IN, inout SurfaceOutput o) {
			half4 c = tex2D (_MainTex, IN.uv_MainTex);
			o.Albedo = c.rgb;
			o.Alpha = c.a;
		}
		ENDCG
	} 
	FallBack "Diffuse"
}

Here is a picture

The only light in the scene is the one visible in the picture.

2

When I tested your shader on a new project, I didn’t see the defect you described.
Try a new project and see if you still get the defect.

3

I have a point light, you have a directional light. Does _LightDir not work with point lights?