Comparing T5 and T8 Grow Lights for Indoor Gardening

T5 High Output Grow Light

While researching indoor fluorescent grow lights, you may have heard that T8 fluorescent lamps are more efficient than standard T12. You may have also heard about the other new fluorescent growing lights, the T5 High Output (HO). So what are the pros and cons of these two different technologies? How do they compare and which is best for your garden?

The Difference

The basic difference between these two fluorescent bulbs is reflected in their names. The T8 bulbs are eight eighths of an inch in diameter (equivalent to 1 inch thick). The T5 bulbs are thinner at 5/8 of 1 inch thick. Many indoor gardeners prefer T8 grow lamps over T12 because they produce more overall lumens than regular T12 fluorescent bulbs, have a longer life and are more efficient.

The advantage of the T5 high output bulbs is that they are even more efficient than the T8, on average by about 9%, can produce more light in a smaller amount of space and use less wattage (75 to 90 lumens per watt). T5 HO also have high color rendering properties (CRI) meaning they are more visually appealing. (The color rendering index is only important when you care about how the light looks to the human eye but not necessarily important to plants, however.)

However, despite higher efficiency, T5 bulbs require different and more expensive fixtures. Another downside is that they tend to have a lower life span of around 10,000 hours as compared to the average 20,000 hours of T12s, and 30,000 hours of T8 tubes. But if you look hard enough, you can find T5 bulbs with longer life spans, so make sure to check this specification before purchasing.


Both the T5 and the T8 bulbs can effectively be used as the main source of lighting, as well as supplemental lighting for your indoor garden. T5 bulbs do emit more lumens and put off more heat than other fluorescent lights, so you may need to use a small fan to keep your plants cool when they are under these bulbs.

Before you go out and purchase your new, more efficient T5 grow light, there’s another, even newer option you will want to consider. This latest fluorescent light technology is called the “Super T8” and is a high output T8 bulb that rivals the efficiency of the T5 HO bulbs, and has a few more advantages, such as longer lifespan.

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