Here is a very helpful guide to avoid backlight problems after the glass replacement of your iPhone.
When preparing to add LOCA onto a cleaned iPhone LCD make sure that you remove the working backlight and apply a non working backlight. This will ensure you do not have LOCA bleed through and ruin your working backlight. Remove the backlight using a soldering iron to remove the 3 prongs that attach the backlight to the LCD cable. Make sure you keep the electrical tape tab that covers the 3 connections and reapply it when you put the good backlight back on. If you leave the backlight connection exposed you have a high probability of shorting the connection on the metal frame of the iPhone which can cause strobing and potentially short the backlight fuse or coil which are both advanced logic board soldering.
Before you apply the clean backlight you Must blow the excess LOCA glue out from the edges of the LCD screen and the flex cables at the top of the LCD assembly. I use a compressor with a fine tip and blow the glue out from every angle. Then place the cleaned screen under the UV lamp again to cure any residual glue on the back side as well. I highly recommend cleaning the surfaces with Pure Isopropyl Alcohol or Pure Acetone. Be VERY gentle when cleaning or lifting or moving the LCD flex cables as they are extremely delicate and can be easily damaged leaving all of your separation process utterly worthless.
When re-soldering the connection on to the cable make sure that all connections line up with their solder otherwise you could also cause a short and strobing.
Make sure you keep the electrical tape tab that covers the 3 connections and reapply it when you put the good backlight back on. Otherwise you will short your backlight out and cause strobing. When re-soldering the connection on to the LCD cable make sure that all connections line up with their solder otherwise you could also cause a short and strobing.