As T5 linear fluorescent light bulbs become more prevalent in the lighting industry, many end users wonder how to decide whether the T5 or T8 is better for their particular needs. Here are some guidelines to help you decide which is best for your application.

Shape
The first place to start is understanding the differences in the shape designations “T5” and “T8.” The letter “T” indicates that the light bulb is a tubular shape, and the number indicates the diameter of the tube in eighths of an inch. A T5 light bulb is tube that is five-eighths of an inch in diameter. A T8 light bulb is a tube that is eight-eighths of an inch (one inch) in diameter.

Efficiency
In general, as a fluorescent tube’s diameter is reduced, its energy efficiency is increased. Therefore, reducing the tube diameter from one inch to 5/8 inch results in a more energy-efficient light bulb. When retrofitting 32-watt T8 bulbs with 28-watt T5 bulbs, you will save four watts of energy per bulb. This may not sound like much, but that is 16 watts saved for every 4-bulb fixture. In a large office building or shopping mall that contains hundreds of these fixtures, the savings can add up pretty quickly. The savings are even greater when retrofitting with T5 high output (T5HO) light bulbs. One T5HO can provide 5,000 lumens – the equivalent of two T8s. This provides even greater energy savings, as well as replacement and maintenance savings with fewer bulbs. However, end users need to consider their specific applications to determine if the increased efficiency of the T5 justifies its increased cost compared to the T8.

Design
Many lighting designers prefer T5 linear fluorescent bulbs over T8 bulbs because T5 fixtures can be much sleeker and more stylish than T8 fixtures due to the T5’s smaller size. Moreover, the smaller size of T5s enables fixture designers to better control the light in terms of optics and glare.

Lumen Maintenance
Both T5 and T5HO bulbs offer better lumen maintenance than T8 bulbs. The T5s retain about 95 percent of their output after 40 percent of their rated life, compared to less than 90 percent for T8 bulbs.

Variety
Because T8 bulbs have been around longer, there is a wider selection to choose from. This allows for more freedom to determine the right lighting conditions for your application because there are so many wattages, lengths, color temperatures, CRIs, and lifespans to choose from. All of these options make it easier to adjust the light levels in your specific application with T8 bulbs.

T5 and T8 fluorescent tube light bulbs both have their advantages and disadvantages. By analyzing your needs against the pros and cons of both bulbs, you can determine which one will work best in your application.