Light is rendered on the graphic card, on a 2D rectangle that fills the screen. Getting the light level requires to download some data from it in a format that is fit for your usage, and is not a practical way in your case.
One naive way could be to have a camera render a tiny portion of the position your character stands, excluding the character (to prevent shadow from interfering) and get pixels from its rendered texture. But I feel this is going to have flaws, and could be tedious to setup right.
I would advise you find a simpler and faster way.
In 2D, what I would do is have a lightmap grid, so I can get lighting values fast and easy. In 3D this can be achieved too, but maybe not as easily.
Or, I would use the physics engine and perform raycasts from nearby light sources to the point I am querying, so i know how many lights can "see" that point, and so I know roughly how much light it has.
All this also depends on why you need this information, how much precision you actually need, and how you want to use it.