Among the major types of HID lighting, Sylvania mercury bulbs have been used for decades and still are in use for many fixtures today.  The technology involved in this lighting is similar to fluorescent lighting. An arc is established between two electrodes in a gas-filled tube which causes a special vapor to produce the light you see. Unlike fluorescent bulbs, this light does not need a coating of phosphors in order to produce the light, the light comes from the arc itself and creates a tremendous amount of light.  Although it doesn't need the coating to produce light, many times it is used with the coated version of the lamp.  In the past, manufacturers tried to make the color more warm by using a coating on the inside of the lamp and that coating is usually referred to as deluxe white.

All the major manufacturers like Sylvania, produce mercury vapor light bulbs in all kinds of wattages and sizes.  It has an excellent construction and has been a top performer among the other brands. Be aware that like fluorescent bulbs, these also have a specific ballast that is used for each wattage.  You can't change from one wattage to another even if the bulb might fit in the socket.  Most of the time the ballast is a core and coil type which is very heavy. The ballast will be clearly labeled as to which type of lamp it operates. So all you have to do is remove the covering and look to the label for lamp operation. If you don't the correct lamp and ballast combination you can reduce both lamp and ballast life and cost yourself more money in maintenance.  A lamp of 100 watt cannot be swapped with a 250 watt and so on.  Keep this in mind when changing lamps or changing a ballast with these special lamps.  These were a popular lamp many years ago for warehouses and gymnasiums because of the white color.  With the advent of metal halide lamps, many people switched to those because they were more energy efficient and didn't lose light output like mercury bulbs did.  They come is various configurations such as mogul base or medium base and an egg shape bulb or as a R40 flood light.  In some cases, it's all that can be used.

Some people wonder about the color of these lamps.  Is there a color shift from different manufacturers?  The answer is a definite yes, and there can be a different color between manufacturers and various lots.  Mercury vapor light bulbs are also notorious for getting a slight greenish color at the end of it's life.  The unfortunate thing is that they can seemingly last forever in that state and people will leave them in place because it's lit.  But the truth is, it should be replaced when that happens.  Be aware that color can shift over time and the only way to get back to the original color is to replace the lamp.  It's sometimes a sign of end of lamp life.  In most architectural specifications, mercury bulbs are being replaced with metal halide, the HID lamp of choice for almost all high light output applications.  With the advent of more efficient lamps, other mercury vapor bulbs are being specified less often.

Some of the most common varieties of mercury vapor light bulbs are as follows: H39KC-175/DX, H37KC-250/DX and the H33GL-400/DX. The second number in these codes pertains to the wattage of each lamp. Of course, there are other far less common wattages, shapes, and sizes available. The various manufacturers have different names for their product, but we stock the Sylvania mercury vapor lamps. We have a large inventory of these lamps for nearly every type of light fixture in the field.  If you need help identifying a bulb, our customer service representatives can help you determine what you have.