XM 20,000k 250w Double Ended Bulb

Pictured to the left is an XM brand 20,000k 250w Double Ended Metal Halide Bulb.

This is called an HQI bulb (Halogen, Quartz, Iodide) which is common in Europe but pretty rare in the United States (most hobbyist use single ended bulbs). Technically it is not a true HQI bulb only Osram bulbs are as they hold the trademark. It is a double ended bulb meaning that it has two contact points unlike the typical single ended mogul screw type base.

Double Ended bulbs lack the outer envelope (outer glass) of the mogul style bulbs. This outer envelope is a UV blocker. Thus the common practice of running halides without glass shields can not be done with double ended bulbs. You must have UV absorbing glass between the bulbs and tank not only to protect yourself but to protect the livestock in your tank.

When handling double ended bulbs it is critical that you do not touch the glass. Any finger prints on the glass can lead to cracking when the bulbs reaches full burn temperature. If you get any finger oils on the bulbs you must clean it with rubbing alcohol to remove the oil.