Light bulbs have all sorts of fancy designations to explain their shape, size, wattage, color temperature, and more. In these designations, the size is always provided in eighths of an inch. This is why the traditional household bulb is called an A19 -- the A stands for Arbitrary and the 19 means that it is 19/8ths of an inch wide, or 2 3/8ths of an inch wide.

Sure, "Arbitrary" seems like an arbitrary name, but many other designations are clearer in everyday language -- for instance, "F" stands for Flame, and looks like a candle flame (used in decorative lighting). "G" stands for Globe and, true to its name, has a nice spherical shape; you might see these above the vanity in a bathroom. And "T" simply means that the light bulb has a tubular shape. So a T8 bulb is a tube-shaped bulb with a one inch diameter.

Fluorescent T8 bulbs have been around since the 1930s. But today they're especially useful as a replacement for T12 bulbs because of their energy efficiency and because of their standardized low mercury specification. As an example, when we look at 4' linear fluorescent tubes, older T12s running at 40 watts offered a relatively low "lumen per watt" ratio, or bulb efficacy. Newer T12s can produce roughly the same amount of light for just 34 watts. But you can easily replace T12s with T8 bulbs that produce just as much light for just 25 watts. Making the switch from T12 to T8 fluorescent lighting is easy because both types of bulbs can usually use the same fixture housing and sockets; only the ballasts and bulbs must be swapped out.

One thing to consider when choosing T8 bulbs is their ability to render colors well. This is designated as CRI -- Color Rendering Index -- and tells you how well a bulb will show the true colors of an object. The highest possible is 100, which you get from incandescent bulbs, but 70 CRI and higher works well in most general lighting applications. You'll find T8 bulbs ranging from CRIs in the 70s to those with CRIs in the 90s; the latter is useful for color critical applications such as paint color shops, printing applications, and dentist offices.

Another point you can consider when choosing any T8s or any fluorescent tubes is mercury content. Fluorescent tubes require some level of mercury because the tubes operate by exciting that mercury, which produces UV rays. The tube phosphors then convert these UV rays into visible light. Since mercury is considered a toxic substance, this is a concern for some people, and they want to minimize the mercury in their bulbs. This is especially helpful if you're trying to make your business greener.

Fortunately, new generations of fluorescent tubes have reduced the amounts of mercury used without lowering the light output. T12s with lower mercury content are sometimes differentiated by the green metal caps at the ends of the linear tube instead of silver caps. Some companies also name their low-mercury lines -- Philips, for instance, uses the term "Alto" to designate their low-mercury line of T12 bulbs. T8 tubes usually use even less mercury, and certainly low-mercury T8s use the least among these tubes.

Since fluorescent bulbs do contain mercury and are considered hazardous waste when broken, recycling is highly recommended. You can take advantage of local or shippable recycling options rather than disposing them in regular office trash. Recycling allows for the containment of exposed mercury gasses and reuse of the glass and metals that make up fluorescent lights.

It is also possible to completely eliminate mercury usage by choosing LED T8 bulbs. LED T8 lighting tubes are a true green technology not only because of their reduced energy usage but also because of their lead-free and mercury-free specifications. They produce no infrared or ultraviolet radiation and reduce light pollution, making them ideal for those that are interested in the international “dark skies” initiative. Admittedly, though, LED tubes cost a good deal more up front at the time of this writing, which is why many businesses continue to use fluorescent T8 bulbs for now.

We hope this helps you understand a little bit more about T8 bulbs and why so many businesses make them their general lighting bulb of choice.