These bulbs are not actually designed to be mounted horizontal,,although they test them in all positions at factory,,they are meant to be operated at base up,or base down..for maximum output,cooling.
When mounting these horizontal,in an enclosure the operating temp does go up,,,you must have proper airflow(ventilation)to keep the ballast cool,vented,it is electronic,and the drivers used get very hot,and have cracked the driver first in line on the circuit,after smoking up the place..these units will not burn ,,but it will stink the place up for days..
The arrow in the pic shows the location of the problem....
