Original backlight for iPhone 7. This is the part to replace when you have marks on the screen on a white background or the home button extension cable is torn.
Replacement backlight for iPhone 7.
This part needs to be replaced when you see marks on the screen against a white background, which is usually caused by moisture.
Since the iPhone 6S, the home button extension cable runs through the backlight, so if you have torn the cable controlling the home button, you will need to replace this part to fix the problem.
The repair requires desoldering the old part and soldering the new one, so you will need a soldering iron and a minimum of experience.