Apparatus for quality film formation

In apparatus including means for forming a coating on a first surface of a transparent vitreous substrate having a variable energy loss distribution adjacent said first surface as said coating is formed during movement of said substrate along a substantially horizontal plane, an improved heating apparatus comprising:

• a plurality of heaters operatively located for heating an entire second surface of said substrate in opposing relationship with said first surface while said coating is formed on said first surface;
• at least one temperature sensor in functional proximity to the portion of the substrate being coated and adapted to detect thermal losses from said portion of the substrate being coated;
• and
• control means responsive to said temperature sensor for selectively energizing at least said heaters opposing the portion of the substrate being coated to establish a thermal energy input distribution along said entire second surface approximating said variable energy loss distribution including said thermal losses from the portion of the substrate being coated.