Here's a simple demonstration of one way I go about the lighting effect, this isn't lightweight, so just use how I have the layers blending in principal to apply to your own needs, I suggest you play around with layer 2's effect, hardlight, multiply etc will yield different results.
Basically I have one layer on top of everything with a solid black background color (helps hides the edges of my sprite image), I set the layers effect to overlay, then I create a sprite on there with my light source image, generally a white circle with a fading to transparent radius. Lastly I change the sprites Blendmode to Additive.
Plus search around the forum, There's probably a smarter, better and more performance friendly method out there
** Edit: Forgot to mention, use your arrow keys to move the light around on the attached example.