Two winters ago I ran a four-foot T5 shop light over my seedling tray, and my electricity bill told the rest of the story faster than the plants did. Since then I have owned both technologies, and the gap in 2026 is wider than most garden-center tags admit. Here is how they actually compare on the numbers that matter.

How Efficient Is Each Light, Really?

The number that matters is photosynthetic efficiency, expressed as micromoles per joule (µmol/J). A modern LED bar reaches 2.5 to 3.0 µmol/J. Good T5 high-output tubes land near 1.0 to 1.5 µmol/J. Put plainly, for the same electricity an LED delivers roughly twice the light your leaves can use. That difference is why a 30W LED can outgrow a 54W fluorescent over a 24-inch shelf.

If you are still deciding on a fixture, the same efficiency figure is what separates a good bar from a weak one. Measure it, do not trust the printed box, and you will avoid the most common buyer regret.

Shop listings still quote lumens, but lumens measure light for human eyes, not leaves. PPFD, given in micromoles per square meter per second, is the number that actually tracks growth. Good LED shelf bars deliver 200 to 400 µmol/m²/s at 6 to 8 inches above the canopy, while a T5 tube tops out near 150 to 250 µmol/m²/s at the same distance. Few buyers notice this gap until they compare two trays side by side under equal wattage.

Heat Output and How Close You Can Place Them

Fluorescent tubes shed real warmth. A 54W T5 runs hot enough that you must keep it 6 to 8 inches above the canopy or you will scorch tender seedlings. LEDs stay cooler at the board, and 3 to 5 inches above the plants is usually safe, though the driver behind the panel can still warm a small room. Less heat also means less watering, since hot air dries the soil faster.

Tomato crops, Solanum lycopersicum, tolerate the extra heat of a T5, while a shelf of soft leafy greens prefers the cooler LED footprint. Distance is a spec, not a guess, so set it by the leaf tips.

In a 10 by 12 foot room, a pair of 54W T5 tubes raised the air temperature by roughly 4 to 6°F (2 to 3°C) near the shelf, while a comparable LED raised it by only 1 to 2°F (0.5 to 1°C). During a summer heat wave that margin decides whether you run a fan, and a fan is another 10 to 20W on the load. Cooler boards also let you place the light closer, which raises the PPFD your plants actually receive without scorching them.

Spectrum Control Is Where LEDs Pull Ahead

With an LED you can buy a board tuned to 3000K for flowering or 6500K for leafy growth, and many full-spectrum bars let you dim from 20 to 100 percent with a dial or app. T5 tubes give you one fixed color temperature, typically around 6400K, and dimming them means buying a separate dimmable ballast. For most hobby growers the fixed T5 spectrum is fine, but once you grow light-hungry crops the tunability matters. See succulent light and temperature needs for the daily hours those plants expect before you spend.

What Is the Real Lifespan and Replacement Cost?

A quality LED is rated near 25,000 hours, which is about 5 to 6 years of evening use. A T5 tube fades to roughly 70 percent output around 10,000 hours and then needs swapping, at about $8 to $12 per tube. Over three years those tube replacements quietly eat the lower upfront price. The choosing and using grow lights guide goes deeper on matching lifespan to how often you actually garden.

Upfront Cost Versus Running Cost

A 2-foot LED bar starts near $25, and a full 4-foot fixture runs $60 to $120. T5 fixtures cost less to buy, often $30 to $50, but you pay on the meter. At $0.15 per kWh, running a 54W T5 for 14 hours a day costs about $41 a year, while a 30W LED doing the same job costs about $23. The LED pays back its higher sticker price in roughly two winters for a single shelf.

Which Plants Each Light Suits Best?

LEDs suit high-light eaters like tomatoes, peppers (Capsicum annuum), and sun-loving succulents that want strong, direct-style light. Fluorescents still do well for low-light foliage, lettuce (Lactuca sativa), and starting seeds where raw intensity is less important. Our low light versus direct sun guide helps you sort which camp your plant falls into before you buy a bulb.

The Verdict: Should You Buy LED or Fluorescent?

For most homes in 2026 an LED wins on running cost, spectrum control, and lifespan. Fluorescent still makes sense for a cheap seed-starting shelf or a dim corner where you only need gentle light and do not want to program anything. If you already own a T5 that works, keep it. If you are buying fresh, the LED math is hard to argue against, and the 2026 grow light roundup lists the exact models that hit those efficiency figures.

Frequently Asked Questions

Q: Can I drop an LED tube straight into my old T5 fixture?

A: Only if the fixture is listed as tube-compatible or you bypass the ballast. Many LED retrofit tubes require rewiring, so check the label before you buy.

Q: How far above the plants should each light sit?

A: Keep LEDs 3 to 5 inches above seedlings and T5 tubes 6 to 8 inches away, then watch the leaf tips for bleaching as your cue to raise them.

Q: Do LEDs really save money over a year?

A: At 14 hours a day on a $0.15 per kWh rate, a 30W LED saves about $18 a year versus a 54W T5, and more if you run longer. Our beginner grow light guide explains what those Kelvin numbers mean in plain terms.

Neither light is wrong, but the efficiency and control of LEDs make them the stronger pick for most 2026 setups, while fluorescents stay useful as a low-cost starting point. Match the fixture to your plant's light appetite, and let the running cost decide when the budget is tight. For model-specific help, the 2026 grow light roundup is the next page worth opening.