T5, T8, T9, and T12 are the most common specifications for fluorescent lamps and LED tubes. Understanding their differences and history will help you make the most accurate judgment when replacing or purchasing lamps.
What does T mean?
In fluorescent and LED tube specifications, the letter “T” stands for Tubular (meaning tube-shaped).
The number following the ‘T’ indicates the tube’s diameter, calculated in increments of 1/8 of an inch.
- 1 inch ≈ 25.4 millimeters (mm)
| Specification | Diameter Calculation | Diameter (mm) | Key Characteristics |
| T12 | 12/8 inch | 38.1 mm (approx. 38mm) | Obsolete Standard, thickest diameter, high energy consumption, largely phased out. |
| T9 | 9/8 inch | 28.6 mm (approx. 29mm) | Earlier standard; was once the most common, now largely replaced by T8. |
| T8 | 8/8 inch | 25.4 mm (approx. 26mm) | Modern common standard; thinner than T9 and more energy-efficient. |
| T5 | 5/8 inch | 15.9 mm (approx. 16mm) | New generation energy-saving standard, thinnest diameter, highest luminous efficacy. |
The evolution of T8 and T9
Before T5 became widespread, T9 was the most common lamp specification in the early days.
- Shared Lamp Holder: T8 and T9 have the same length, and their lamp holders (G13 interface) can be shared.
- Energy-saving alternative: The T8 has a slightly smaller tube diameter than the T9 (26mm vs 29mm) and lower wattage. Because the T8 is more energy-efficient while maintaining similar brightness, it has gradually replaced the T9 as the mainstream choice.
The main differences between T5 and T8
Although T8 replaced T9, the emergence of T5 represents a new generation of energy-saving technology standards.
Energy saving and light efficiency
- T5 has higher luminous efficacy: The T5’s smaller tube diameter technology results in higher internal gas pressure, and its luminous efficacy (lumens/watt) is about 30% higher than that of T8 in the fluorescent lamp era.
- LED Trends: Upgrading to LEDs, whether T5 or T8, significantly improves luminous efficacy. However, T5 LEDs still offer better system efficiency in certain designs due to their more compact structure.
Interface
The T5 lamp holder is completely incompatible with the T8/T9. Although they are both approximately 4 inches in length (with slight differences, the T5 is about 5cm shorter), the T8 and T9 connectors are 13mm pitch G13 two-pin connectors, while the T5 lamp holder connector is a 5mm pitch G5 two-pin connector. If your light fixture has a T8/T9 bracket, you can only replace the T8 LED tube; if you want to switch to T5, you will need to replace the entire light fixture or bracket.
Application scenarios and purchase suggestions
1. Home Replacement
Old Lamp Holders: If you have old T9/T8 lamp holders at home, simply purchase T8 LED tubes to replace them. This is the most economical and quickest way to upgrade your energy efficiency.
2. Commercial/New Installation
For ultimate lighting performance: In brand-new commercial spaces, offices, or venues with high design requirements, prioritize T5 LED luminaires. Their slimmer tube diameter enhances the design aesthetic, and the system efficiency is typically superior.
Replacement Reminder
When purchasing T5 or T8 LED tubes to replace your old fluorescent tubes, a crucial technical choice directly impacts installation methods, energy efficiency, and safety. You need to confirm which type of LED tube it is:
1. Bypass Ballast (Direct Power Supply)
This type of LED tube is incompatible with the ballast in older lighting fixtures. The ballast inside the fixture needs to be completely removed or disconnected so that the power supply current can directly pass through the two ends of the tube.
- Advantages: Removing the ballast eliminates its energy consumption, maximizing the luminous efficacy (lm/W) of the lamp, making it the most energy-efficient and longest-lasting solution.
- Installation Requirements: The wiring modification must be performed by personnel with electrical knowledge.
2. Ballast-compatible (Plug-and-Play)
This type of lamp has a built-in special driver that can be directly inserted into the lamp holder of the existing lamp, preserving and being compatible with the ballast in the lamp.
- Advantages: Installation is extremely simple and convenient. Just unplug the old light tube and plug in the new LED light tube for plug and play.
- Disadvantages: The ballast still consumes a small amount of power while operating, and the lifespan of the LED tube is limited by the lifespan and quality of the ballast. If the ballast fails, the tube will not light up.
About Us: Shaoxing Chanty Lighting
Shaoxing Chanty Lighting Co., LTD. specializes in providing professional, high-quality LED lighting products.
We offer a comprehensive range of T5 and T8 LED Tube Lights, as well as various Commercial and Industrial Lighting Solutions, including high-efficiency panel lights, linear fixtures, and high bay lights. We are committed to meeting all your needs for energy efficiency and reliability through superior product quality and systemic solutions.
For customized lighting solutions, product inquiries, or quotations, please contact us.
And If you’d like to learn more about lighting, LED technology, or fixture selection, feel free to explore our knowledge base for more practical guides and tips.
