I wrote a little MEL script to toggle “Use Flat Lighting” to quickly preview textures during the CG look development process on the project I’m currently working on. I find it particularly useful to assign to a hotkey. I use “8” because it’s right after “7” which is “Use all lighting” and also because I’ve no use at all for the default artisan thingy ever since I started using Maya. Hope you’ll find this useful. =)

//Run script directly or save as a hotkey to quickly toggle "Use Flat Lighting" on current viewport
//Author: Ronald Fong
//Date: 8 Dec 2015
global proc rf_toggleFlatLighting()
{
    string $currentPanel = `getPanel -withFocus`;
    if ( `modelEditor -q -dl $currentPanel` == "default") {
        modelEditor -e -dl flat $currentPanel;
    }
    else {
        modelEditor -e -dl "default" $currentPanel;
    }
}
rf_toggleFlatLighting();