You have been using the Flip normal map button which was indispensable to you in older versions of Lumion but now it does not seem to be available in Lumion 10.3 and newer.

1. Here's how to use the Flip Normal Map function:

The button is still there but the functionality has changed slightly in version 10.3 and newer to 12.5.

• 10.0.2 and older versions: When you assign a Standard Material to an Imported Material, you will get a default (plain) Normal Map.  When you click on the Flip Normal Map direction button, it will generate a Normal Map based on the embedded texture from your modeling software.
• 10.3 to 12.5: When you assign a Standard Material to an Imported Material, you will still get a default (plain) Normal Map.

1.1: The difference is that you have to click on the Remove Normal Map button to delete the default (plain) Normal Map.  

1.2: Then click on the Create Normal Map from Color Map button to create a Normal Map based on the embedded texture from your modeling software.

1.3: Once that's done, you can flip the Normal Map direction with the Flip Normal Map Direction button, just like in older versions of Lumion.

Applicable to:

• Lumion 10.3 and newer through to 12.5.