Metal halide light bulbs with a regular medium base are a replacement bulb used in many types of applications like warehouses, security lighting and other places where high illumination is desired. They have a brilliant white light which is also very energy efficient. If you have space where color matters, then this would be a good choice for general lighting. You'll see them used in critical color areas where the yellow color of high-pressure sodium won't do. These lamps have a universal burn and can be lighted in almost any position. The medium base that screws into the socket is standard; you'll notice that it's much smaller than a mogul base. Of course, these lamps need to operate on the correct ballast, and the lamp wattage needs to match up. The ballasts are not interchangeable with various lamp wattage, so if you have a 100 watt, you need a 100-watt ballast made for it. There is still a large base of installation of these type of light fixtures, and we have this as a replacement light bulb for those of you who still do. These metal halide light bulbs still create a very effective light source that is energy-efficient and does well for many types of industrial and commercial lighting applications. We've reduced the price of many of our HID (high-intensity discharge) lamps and if you're looking for a quantity price, give us a call, and we can help you with that. If you're interested in replacing these with something more energy-efficient, we do have LED options that can be directly replaced or complete new fixtures to replace them. If you have older fixtures, then getting a new fixture probably makes sense especially if there are utility rebates in your area that would apply. But if you're keeping this system, for now, we have all the different wattages that you may need and reliable brands that last longer and are better with the light color shift. Sometimes these metal halide lamps can shift color over their life, and many do on occasion. That's why they won't look exactly the way they did when you first installed them. They deteriorate, and so when they get to a certain point where the color is either shifted too much, or the light output has gone down, it's best to replace them even before they're out so you can still get the effective light that you're trying to get with them. If you find that replacing them with a new bulb doesn't work and it won't light, then you're going to need a ballast, and we have those as well. Keep in mind that these are NOT mercury vapor light bulbs that is a different yet similar kind of light. If you're unsure about what you have or how it operates, we can probably help you with some expertise as we've been selling these for decades and probably have the answer you're looking for.