How do Image shaders interact with UI Canvas draw order?

Problem

I have a simple 2D lighting setup using two custom shaders (one for lights, one for sprites) attached to Image components in a UI Canvas (introduced in Unity 4.6). When the Canvas is in Render Mode 'Screen Space - Overlay' everything works as intended. However, in Render Mode 'Screen Space - Camera', my light is being drawn behind everything.

Can somebody help me fix my shaders (and/or my camera setup?) so that the light is drawn on top of the background in 'Screen Space - Camera' mode? Please see the reference section below for shader source code!

Example

RENDER MODE OVERLAY -- WORKING AS INTENDED

RENDER MODE CAMERA -- SOME KIND OF DEPTH ISSUE -- NO LIGHTING:

Reference: Sprites, Shaders, and Camera

LIGHT SOURCE:

 Shader "UI Lights/Light"
 {
     Properties
     {
         _MainTex ("Light Texture", 2D) = "white" {}
         _LightColor ("Light Color", Color) = (1.0, 1.0, 1.0, 1.0)
         _LightIntensity ("Light Intensity", Range(0.0, 2.0)) = 1.0
     }
     
     SubShader
     {
         Pass
         {
             Blend DstColor One, Zero One
             
             CGPROGRAM
             #pragma vertex vert
             #pragma fragment frag
             
             //user defined variables
             uniform sampler2D _MainTex;
             uniform float4 _LightColor;
             uniform float _LightIntensity;
             
             //in/out structs
             struct vertexInput
             {
                 float4 vertex : POSITION;
                 float2 uv_MainTex : TEXCOORD0;
             };
             struct vertexOutput
             {
                 float4 vertex : POSITION;
                 float2 uv_MainTex : TEXCOORD0;
             };
             
             //vertex
             vertexOutput vert(vertexInput v)
             {
                 vertexOutput o;
                 o.uv_MainTex = v.uv_MainTex;
                 o.vertex = mul(UNITY_MATRIX_MVP, v.vertex);
                 return o;
             }
             
             //fragment
             float4 frag(vertexOutput i) : COLOR
             {
                 float4 lightValue = tex2D(_MainTex, i.uv_MainTex);
                 return _LightIntensity * _LightColor * lightValue;
             }
             
             ENDCG
         }
     }
 }

BACKGROUND:

 Shader "UI Lights/Lit"
 {
     Properties
     {
         _MainTex ("Sprite Texture", 2D) = "white" {}
     }
     
     SubShader
     {
         Cull Off
         
         Pass
         {
             Blend SrcAlpha OneMinusSrcAlpha
         
             CGPROGRAM
             #pragma vertex vert
             #pragma fragment frag
             
             //user defined variables
             uniform sampler2D _MainTex;
             
             //in/out structs
             struct vertexInput
             {
                 float4 vertex : POSITION;
                 float2 uv_MainTex : TEXCOORD0;
             };
             struct vertexOutput
             {
                 float4 vertex : POSITION;
                 float2 uv_MainTex : TEXCOORD0;
             };
             
             //vertex
             vertexOutput vert(vertexInput v)
             {
                 vertexOutput o;
                 o.uv_MainTex = v.uv_MainTex;
                 o.vertex = mul(UNITY_MATRIX_MVP, v.vertex);
                 return o;
             }
             
             //fragment
             float4 frag(vertexOutput i) : COLOR
             {
                 float4 col = tex2D(_MainTex, i.uv_MainTex);
                 return float4(col.rgb / 2.0, col.a);
             }
             
             ENDCG
         }
     }
 }

CAMERA: