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How to Choose the Right Size and Wattage for LED Tubes?

Aug 04, 2025

How to Choose the Right Size and Wattage for LED Tubes

LED tubes are a popular choice for lighting in homes, offices, warehouses, and shops. They use less energy, last longer, and produce better light than traditional fluorescent tubes. But to get the most out of LED tubes, you need to choose the right size and wattage. Picking the wrong size can make installation impossible, and the wrong wattage might leave your space too dim or waste energy. This guide will help you select the perfect LED tubes by breaking down size and wattage considerations, step by step.

Why Choosing the Right Size and Wattage Matters

Before diving into details, it’s important to understand why size and wattage matter for LED tubes.

Size affects whether the LED tube will fit in your existing light fixture. If the tube is too long or too thick, it won’t fit, and you’ll have to return it or modify the fixture—wasting time and money.

Wattage determines how much energy the LED tube uses and how bright it is. A wattage that’s too low will leave your space dim, making it hard to work or move around. A wattage that’s too high will waste electricity, increasing your bills, and might even make the space uncomfortably bright.

LED tubes are designed to replace old fluorescent tubes, so getting the size and wattage right ensures a smooth swap, keeping your lighting efficient and effective.

How to Choose the Right Size for LED Tubes

LED tubes come in different sizes, and the key is to match the size of your existing fixture or the space where you plan to install them. Here are the main factors to consider:

Length

The most common lengths for LED tubes are 2 feet (60cm) and 4 feet (120cm), though you can also find 1 foot (30cm), 3 feet (90cm), and 8 feet (240cm) options. To find the right length:

Check your existing fixture: Measure the length of the fluorescent tube you’re replacing. LED tubes need to fit into the same space, so the length should be the same. For example, a 4-foot fluorescent tube should be replaced with a 4-foot LED tube.
Measure the fixture itself: If you’re installing a new fixture, measure the inside length of the fixture. The LED tube should be slightly shorter than this to fit easily—usually by about 0.5 inches (1cm).

Choosing the wrong length is one of the most common mistakes. A tube that’s too long won’t fit, and one that’s too short might rattle around in the fixture, causing damage.

Diameter (Tube Type)

LED tubes are labeled with a “T” followed by a number, like T8 or T5. This “T” stands for “tubular,” and the number refers to the diameter in eighths of an inch. For example:

T8: 1 inch in diameter (8/8 = 1)
T5: 5/8 of an inch in diameter
T12: 1.5 inches in diameter (12/8 = 1.5)

The diameter must match your fixture. Most modern fixtures use T8 or T5 tubes, while older ones might use T12. To check:

Look at the existing tube: It will usually have “T8,” “T5,” or “T12” printed on it.
Measure the diameter: Use a ruler to measure across the tube. If it’s 1 inch, it’s T8; 5/8 inch is T5; 1.5 inches is T12.

LED tubes are often designed to fit into fixtures made for older types. For example, T8 LED tubes can sometimes fit into T12 fixtures, but it’s best to check the product description to be sure.

Socket Type

LED tubes connect to fixtures using sockets, and the type of socket determines how the tube is installed. The two main socket types are:

G13: The most common socket, used for T8 and T12 tubes. It has two pins on each end, spaced 13mm apart.
G5: Used for T5 tubes, with two pins on each end spaced 5mm apart.

To find the right socket type, check your existing tube or fixture. The pins on the end of the tube will match the socket in the fixture. Using a tube with the wrong socket type will make it impossible to install.

Installation Type (Single-End vs. Double-End)

LED tubes can be wired in two ways, which affects how they connect to the fixture:

Double-end powered: The tube gets power from both ends, like traditional fluorescent tubes. This is the most common type and works with most existing fixtures (after removing the old ballast, in some cases).
Single-end powered: The tube gets power from one end only. This is simpler to install but requires a fixture that can be wired for single-end power.

Check the product label to see if the LED tube is single-end or double-end powered. If you’re replacing a fluorescent tube, double-end powered LED tubes are usually the safest choice, as they’re more likely to work with your existing setup.

How to Choose the Right Wattage for LED Tubes

Wattage measures how much energy the LED tube uses, but it’s also linked to brightness. However, LED tubes are more efficient than fluorescent tubes, so a lower wattage LED can produce the same brightness as a higher wattage fluorescent. Here’s how to choose:

Understand Brightness (Lumens, Not Just Watts)

Brightness is measured in lumens, not watts. For example, a 40W fluorescent tube produces about 2,600 lumens, while an 18W LED tube can produce the same amount. When choosing LED tubes, focus on lumens to get the right brightness.

Low brightness (1,000–2,000 lumens): Good for small spaces like closets, pantries, or hallways.
Medium brightness (2,000–4,000 lumens): Suitable for offices, kitchens, or living rooms.
High brightness (4,000+ lumens): Needed for large spaces like warehouses, garages, or retail floors.

Check the product packaging for the lumen count. This will tell you exactly how bright the LED tube is, regardless of wattage.

Match Wattage to the Space

The wattage you need depends on the size of the space and how you use it. Here are some general guidelines:

Small spaces (closets, bathrooms): 6–12W LED tubes (1,000–2,000 lumens).
Medium spaces (bedrooms, home offices): 12–18W LED tubes (2,000–3,000 lumens).
Large spaces (living rooms, offices): 18–24W LED tubes (3,000–4,500 lumens).
Very large spaces (warehouses, gyms): 24–40W LED tubes (4,500+ lumens).

If you’re replacing a fluorescent tube, use this simple swap: A 40W fluorescent tube = 18–22W LED tube; a 32W fluorescent tube = 14–18W LED tube. This ensures you get the same brightness with less energy.

Consider Color Temperature

While not directly related to wattage, color temperature affects how the light feels, which can impact how bright the space seems. Color temperature is measured in Kelvin (K):

Warm white (2,700–3,000K): Soft, yellowish light, good for homes or bedrooms.
Cool white (4,000–5,000K): Bright, blueish light, better for offices, kitchens, or workspaces.
Daylight (5,000–6,500K): Very bright, similar to sunlight, ideal for warehouses or retail.

A space with cool white light might feel brighter than the same lumen count in warm white, so you might need slightly lower wattage (fewer lumens) with cool white if you prefer a brighter feel.

Installation Tips for LED Tubes

Once you’ve chosen the right size and wattage, proper installation ensures your LED tubes work well and last long:

Remove the ballast (if needed): Fluorescent fixtures use a ballast, but most LED tubes don’t need one. Check if your LED tube is “ballast bypass” (requires removing the ballast) or “ballast compatible” (works with the existing ballast). Ballast bypass is more energy-efficient in the long run.
Check wiring: Follow the manufacturer’s instructions for wiring, especially for single-end powered tubes. Incorrect wiring can damage the tube or cause a fire.
Clean the fixture: Dust and dirt can block light, so clean the fixture before installing the new LED tubes.
Test before finalizing: Turn on the power to make sure the LED tubes light up properly before securing them in place.

FAQ

How do I know the size of my existing fluorescent tube?

Check the tube for labels like “T8 4ft” or measure it: length (from end to end) and diameter (across the tube). The diameter will tell you if it’s T5, T8, etc.

Can I use a higher wattage LED tube than my old fluorescent tube?

You can, but it’s unnecessary. LED tubes are brighter per watt, so a lower wattage LED will often be enough. Higher wattage will use more energy and might make the space too bright.

Do LED tubes fit all fixtures?

No. They need to match the length, diameter, and socket type of the fixture. Most modern fixtures work with T8 or T5 LED tubes, but older ones might need specific types.

How long do LED tubes last?

Most LED tubes last 50,000–100,000 hours, which is 5–10 times longer than fluorescent tubes. This means you’ll replace them far less often.

Do I need to hire an electrician to install LED tubes?

If you’re replacing a fluorescent tube with a ballast-compatible LED tube, you can do it yourself. For ballast bypass installations, it’s safer to hire an electrician, especially if you’re not comfortable with wiring.