Quote Originally Posted by louisville97
I don't know if it makes any difference, but all my ballasts were originally vertical bulb units. So you don't think it will cause any harm if I switch it over to horizontal and paying no attention to bulb position? I was curious as to why the sockets for the horizontal ones specified bulb position. They are only 400w and don't throw off near as much heat as all my 1000w do, so I thought it would be okay to convert. I just read justa's second part and I think I might try to contact a bulb or ballast manufacturer and see what they say. All of the ballasts I have were made only about 10 miles from here so I might give them a shout on Monday morning. I have seen many MH parking lot and security lights mounted sideways but was told you shouldn't. Thanks again.

The bulbs wont explode unless you break them.
However hanging a bulb incorrectly will reduce its life ALOT.
For example I have a 400W MH/HPS switchable ballast, Horizontal bulbs I must let my light cool until I can touch it without burn before I can move it(raise or lower)My reflector(bulb holder) is on chains I have to move 1 at a time so at moving my bulb its position will go from - to / and if its hot my bulb will deteriorate at a rapid rate. If you do this when its real hot it may not come on again I had one do this to me my supplier asked a few questions then explained why it happened.
Contact your supplier they will be able to help you more than anyone here can.
DFG