as I understand it all HPS bulbs can be used in any position?,mh bulbs say if they are vertical or horizontil,even CMH bulbs that run on an hps ballast are position oriented meaning you must buy vert. or horizontil CMH bulbs .this is what I have read somewhere?
this info is from EYE....some may be specific to their lamps but some of the "codes" listed (Like U for Universal) are fairly standard in the industry.