title: Lighting covering up sky
body: <p>I have a 2D tile-based lighting system which is drawn onto a Render Target.
  I am also drawing a background which involves mountains, sun/moon, and clouds.
  There is also the unlit game; blocks, character, etc.</p>
  
  <p>Here is the order in which everything is drawn:</p>
  
  <pre><code>1. Background
  2. Game World
  3. Lighting
  </code></pre>
  
  <p>The problem is that the LIGHTING is covering up the BACKGROUND when it's dark:</p>
  
  <p><img src="https://i.stack.imgur.com/sjZdj.png" alt="The moon and background is covered by darkness."></p>
  
  <p>Although it's perfectly fine in the day because the light is full:
  <img src="https://i.stack.imgur.com/hrtn0.png" alt="The alpha of the light is 1, so the background is visible"></p>
  
  <p><strong>You might ask, well, why don't you just blend each block, not drawing the lighting on a RenderTarget?</strong></p>
  
  <p>Because that would prevent me from performing smooth lighting, as seen in the pictures. To produce the smooth lighting, I draw squares of light onto a RenderTarget, perform a Gaussian blur and then draw that RenderTarget.</p>
  
  <p><strong>How about not drawing a square of light in empty spaces?</strong></p>
  
  <p>The light blurs onto any adjacent blocks, and not all objects in my game affected by lighting are square, so they would look like a sprite with a blurry square on top of it.</p>
  
  <p>Light NOT being drawn in empty spaces:
  <img src="https://i.stack.imgur.com/j8fUA.png" alt="Light NOT being drawn in empty spaces"></p>
  
  <p>Light being drawn everywhere:
  <img src="https://i.stack.imgur.com/uZ7LG.png" alt="Light being drawn everywhere"></p>
  
  <p>Is there any way to keep the background visible, or something else that would help my predicament?</p>