T5 vs T8

T5 vs T8: The Ultimate Grow Lamp Comparison

When discussing T5 vs T8 grow lights, there are many different aspects to consider. A lot of people will argue that the T8 is cheaper and is known to be efficient whereas other people will point out that T5 grow lights have excellent long-term saving potential and a better quality of light. All of these arguments and many more will be addressed in this article so that you can decide which is the better lamp for you and your plants.


Arguably the most important aspect to consider in the T5 vs T8 debate is, which bulb has the better efficiency of each light. After all, the more efficient a bulb is, the more money you’ll save and the better quality produce you’ll grow. When looking at the efficiency of each bulb, it’s important to consider two major areas: the quantity of light and the quality of the light.

Quantity of Light

The quantity of light produced can be judged by the amount of Lumens Per Watt the light emits, as this indicates how much light is emitted per unit of power. The T5 is dominant in this area of the T5 vs T8 comparison, as it produces 100 Lumens per Watt which is considerably more efficient than the T8 which produces 90 Lumens Per Watt – so the T5 produces more light using the same amount of power.

Quality of Light

The quality of light is calculated through the Colour Rendering Index (RMI.) In terms of quality of light, both the T5 and T8 are equal as they have a CRI of 85.

Whilst both the T5 and T8 produce the same quality of light, it’s important to note that the T5T5 vs T8 produces a higher quantity of light so it can produce more high-quality light whilst using less energy than the T8, thus making it the more efficient of the two lamps. When analysing the T5 vs T8 comparison, it’s also worth noting that the T5 is also more useful when encouraging bloom in a plant which makes the light a lot more versatile.

Heat Output

All grow lamps produce heat and this can have a direct effect on their effectiveness as too much heat can damage the plants. Both lamps operate at a relatively low heat, with the T5 working at 95 Degrees Fahrenheit and the T8 working at 100 Degrees Fahrenheit. This is useful because it allows you to position both lights closer to the plants so that they can receive more light. However, when evaluating the heat output of the T5 vs T8,  the T5 again emerges as the more productive lamp because that extra reduction in heat allows it to move closer to the plants and thus light them more effectively than the T8.

T5 vs T8: Financial Factors

Whilst T8 light bulbs are cheaper to buy than T5, it’s important to consider the long-term financial factors of the T5 vs T8 argument.


The T5 has a lifespan of 20,000 hours which is much larger than the 15,000 hours lifespan of the T8. Whilst you won’t have to replace a T8 very often, if you plan on growing over a long period of time then you’re still going to have to replace it a lot more frequently than you would have to replace a T5.

If you consider that there are 87000 hours in a year, this means you would have to replace your T8 light 5 times during that period whereas you’d only have to replace the T5 three times, allowing you to save money on replacement bulbs in the long run.


The T5 operates at much lower 28 Watts which is much lower than the T8  which operates at 36 Watts. The lower wattage means it requires less electricity to run the T5 which will allow you to save money on your energy bill both short term and long term.


As mentioned above, the T5 is the more efficient lamp of the two and will help you to grow high-quality produce. This is important to consider if you plan to sell the produce as you can command a greater fee for better quality produce and you can also use the enhanced lighting capabilities to grow produce quicker and can thus grow more of it over a period of time.

When you take into account the reduction in energy, higher-quality produce and longer lifespan of the T5, it’s easy to see that this is a much more financially beneficial option than the T8 and is clearly the better light in the T5 vs T8 debate.


When looking at the size of a grow light, it’s important to understand what the numerical value in T5 and T8 represents. The numerical value here represents the diameter of the lamp and is measured in 8ths of an inch. Understanding this, we can see that the T5 is the smaller of the two at 5/8 of an inch in diameter whereas the T8 is 8/8 (1 inch) of an inch in diameter.

This is important because the smaller light can be placed in smaller areas. This means that you can be more flexible with how you position your lamp in your grow chamber and can ensure that every plant receives the light it needs.


The function of the ballast is to control the flow of electricity to the bulb and both the T5 and T8 have different ballasts. Whilst the T8 uses a somewhat dated magnetic ballast, the T5 works with the more popular and energy efficient electronic ballast. Key facts about each ballast are listed below.

Magnetic Ballast

  • Conducts electricity through one wire causing an inconsistent flow
  • Produces a flickering sensation in the bulbs
  • Creates a high pitched buzzing noise
  • Operates at 60 Hertz (Hz)

Electronic Ballast

  • Conducts electricity through a series of unconnected coils to produce a consistent flow
  • No flickering in the bulb
  • Operates very quietly
  • Smaller than a magnetic ballast
  • If one lamp breaks the other lamps will continue to work on the ballast
  • Works at a frequency of 20000 Hz

The ballast is one area in the T5 vs T8 debate that is completely dominated by the T5 as the electronic ballast is much more energy efficient to use and produces a much higher quality of light. Most magnetic ballasts are being gradually replaced by electronic ballasts across several industries because of how much better the quality is from an electronic ballast.

T5 vs T8 Retrofit Conversion

If you’ve been using a T8 and want to change to a T5, there is a way to alter your current fittings so that you don’t have to replace them. Using a Retrofit Converter you can convert your current T8 fitting so that they fit into a T5 and you can then use T5 tubes going forward. These converter kits bypass the T8’s magnetic ballast and use a new more energy-efficient ballast which reduces the Wattage to make it compatible with a T5. Retrofit Converters are a great way to save money and have been known to cut energy usage by 65%.

A Comparison Chart

The table below highlights the differences in the key factors between the two bulbs in the T5 vs T8 comparison.

 Lumens Per WattColour Rendering IndexSizeCostLifespan (Hours)Temperature (Degrees Fahrenheit)
T5 Light Bulb100855/8 of an inch$5 - $1020,00095
T8 Light Bulb90851 inch$3 - $515, 000100

As you can see, the T5 is clearly the more efficient light bulb in the T5 vs T8 comparison.


Whilst the debate about T5 vs T8 is an ongoing battle, it’s gradually becoming clearer just how much better the T5 actually is. Whilst the T8 may cost less to buy initially, the longer lifespan and energy saving benefits of the T5 will help you to save a lot of money in the long run. Also, because of it’s smaller size and the higher quantity of light it produces, you can encourage greater plant growth using the T5.