[EDIT: Update, had to reopen to reseat keyboard backlight connector, so again unplugged and replugged display connector - now when I shine a light through apple logo I can see the screen displayed, just no backlight.]
I am having a similar, but not exactly the same, problem: I get no backlighting (apple logo does not light up), and shining a light through it does not show anything.
One night I had an external hooked up via HDMI, watching a movie or something, turned my brightness all of the way down, and the next day my screen would not come on, but works perfectly with external. Brightness controls work, just nothing happens with the screen. A couple drops of rain may have gotten on it, not soaked just a couple/few drops - nothing else was affected (eg isight works).
I have opened the case and unplugged, inspected (seeing nothing of note) the cable, replugged, and closed the case. Have not tried using any electrical contact cleaner yet, but will do so later.
[Edit: Adding pic September 18, 2019… this pic isn’t very good, but it shows the connector in the monitor I mentioned in my later comment.]
Narrowed down the problem to the display inverter:
Does anyone know where to get these?