I want to render a transparent image that preserves object and light source information. How do I do
Welcome 
,
hmmm 
the glowing would only be visible if there is some “athmosphere” or volume… maybe just do it in compo:
Thank you very much for answering my question, but this effect is not what I want.
First, I want to make a transparent image material to compose. He has to satisfy the following points.
1: It must be transparent format.
2: He must have a reflection of the ground, but the ground is not visible.
This is a little bit more complicated, what you can do is make the wall black, make the light white, and use the render as a mask for your compositing.
Here are some screenshots of a simple test file:
This is the render with all collections visible
This is with the Light collection set to Indirect Only, this will be used as the mask.
Here is the render of the actual light, with the Plane collection set to Indirect only, and the Film set to transparent in blender.
Here is how the compositing looks in blender, I added some curves because the light on the plane was not bright enough.
Here is how the final combined Light + Light affecting the wall
And here is how the final comp looks like, when adding the PNG over an image in PS.
The only drawback with this, is that the wall need to be darker than white, because it’s not 100% correct compositing, as the light affecting the wall should be set to Add, but it works fine for most cases.
I see… your initial image suggested a more 2D or low-poly asset target for me but i newer thought about using something like this in a more highpoly environmnet since the light distribution depends on the complete geometrie… that’s the reason why blender exist or everbody would use photo bashing… 
You see: precide questions leads to precice answers and i think @sergioValente made a nice mini tutorial.
This kind of technique is usually used for online shopping experiences or configurations.
You can have a better experience with smaller file sizes if only load 1 background, and 100pngs of lights, than loading 100 full renders.