Single ended or mogul socket bulbs have a screw in base. Doubled ended are HQI bulbs and don't have screw ends. The ends of the bulb just slip into the fixture. I am not an expert here but I don't think single ended bulbs can be HQI.
HQI or double ended bulbs have to have a UV
shield where the single ended bulbs do not as it is built into the glass.
I have heard that HQI are brighter but not sure really. I have a 150 HQ over a prop tank and I use 250 watt single ended bulbs over my display. No comparison for output here.
*180 gal Display, 100 gal basement sump, 33 gal refugium, 3x250 MH, 2x160 VHO actinics, zoos, some softies, LPS & lots of acros and other SPS.
*100 gal prop tank plumbed into main system w/ 2x96 PC lights and 1x150 MH,