This comparison is worth having because the answer is less lopsided than the marketing suggests, and because the thing that actually decides whether seedlings grow well is neither technology.
What decides it is delivered light at the canopy. Vegetable seedlings want a daily light integral of 12 to 17 moles per square meter per day, which over a 16 hour photoperiod means a sustained 210 to 300 micromoles per square meter per second at leaf height. A fixture that delivers that is a good fixture; one that does not is not, regardless of what is inside it.
Light falls off sharply with distance, so hanging height matters as much as the fixture. This is why a modest strip a few inches above a tray outperforms a powerful fixture three feet up, and why a wattage figure on a box tells you almost nothing useful. Check any candidate with the DLI and PPFD calculator.
The comparison
| Measure | LED strip | T5 fluorescent |
|---|---|---|
| Photons per watt | Higher, and improving generation to generation | Lower, and essentially fixed |
| Lifespan | Tens of thousands of hours | Thousands of hours, with output falling well before failure |
| Output decline | Gradual and slow | Noticeable within a year of daily use |
| Heat produced | Low, so fixtures can sit close to foliage | Moderate, and the tube itself is warm |
| Cost per fixture | Low and falling | Low |
| Replacement parts | Usually the whole fixture | Tubes replaceable, fixture reusable |
| Dimming and control | Common on better fixtures | Rare |
| Spectrum | Chosen by the manufacturer, usually full spectrum white | Determined by the phosphor, commonly 5000 K or 6500 K |
| Fragility | Solid state, tolerates knocks | Glass tube, breaks |
| Suitability for propagation | Excellent | Perfectly adequate |
Spectrum, and why full spectrum white is the right choice
Purple grow lights exist because chlorophyll absorbs most strongly in the red and blue bands, and an emitter that produces only those wavelengths is more electrically efficient. That reasoning is sound and it leads to a fixture that is unpleasant to work under and makes it impossible to see plant colour.
For propagation, full spectrum white is the sensible choice. Plants use green light perfectly well, particularly deeper in a canopy where red and blue have already been absorbed by upper leaves. And crucially, under white light you can see when a seedling is pale, when a leaf is yellowing, or when aphids have arrived. Under purple light none of those are visible until they are severe.
Colour temperature in the 4000 to 6500 K range is all suitable for seedlings. Barrina 4 ft LED Grow Lights, 5000 K, 6-Pack at 5000 K is a straightforward example, and Barrina T8 2 ft Grow Lights, 5000 K, 6-Pack ($71.24) covers a shorter bench at the same colour temperature.
Heat, which is a bigger deal than it sounds
LEDs run cooler at the emitter than fluorescent tubes do, and that changes how close a fixture can sit to foliage. Since delivered light falls off sharply with distance, being able to hang a fixture two inches above a tray rather than six is a substantial gain in delivered PPFD from the same fixture.
In a propagation space the waste heat is not entirely wasted, though. Fluorescent tubes over a bench in a cool room contribute usefully to air temperature, and growers who switch to LED sometimes find the bench is measurably cooler afterwards. That is a good problem, and the correct fix is bottom heat under the tray rather than warmer air, because germination and rooting respond to medium temperature rather than air temperature.
Mount either type on OneChoi Adjustable Rope Light Hangers, 8 ft ($35.00) so the height can rise with the plants. A fixture at a fixed height is at the wrong height for most of the crop life.
The cases where fluorescent is still the right buy
- A single bench used for a few weeks a year. Efficacy differences matter in proportion to running hours, and a fixture used for eight weeks each spring accrues very little.
- An existing fixture with life left in it. Replacing a working T5 setup with LED to save electricity rarely pays back at hobby scale.
- A shop fitting already in place. A Hydrofarm Jump Start T5 2 ft Strip Fixture with Lamp ($49.95) or a SunBlaster T5 High-Output 3 ft Strip Light ($42.29) is a proper horticultural fixture with a reflector, which is a better starting point than any general-purpose LED strip without one.
- Replaceable tubes. A fluorescent fixture outlives its tubes, whereas most cheap LED strips are replaced entire. Over a long enough horizon that is a real difference in waste as well as cost.
What actually matters more than the choice
- Hang it close. A few inches above the canopy, raised as the plants grow. This single factor swamps the difference between technologies.
- Run a long photoperiod. Sixteen hours is standard for seedlings and up to 18 is tolerated. A BN-LINK 7-Day Programmable Digital Timer Outlet ($13.99) makes it consistent, and consistency matters more than peak intensity.
- Cover the whole tray. A fixture narrower than the bench leaves edge plants short, and they stretch toward the middle. Two narrow strips beat one wide beam for uniformity.
- Measure it once. A DANOPLUS Quantum PAR Meter, PPFD Tester ($79.99) tells you what is actually arriving at leaf height, which no specification sheet can. Even a single reading recalibrates every future decision about hanging height.
- Do not confuse light with heat. Bottom heat for germination, light for growing on. A VIVOSUN 10 x 20.75 in Seedling Heat Mat and Digital Thermostat Set ($24.78) does the first job at a fraction of the wattage any lighting change would.
Propagation lighting
Lighting is one input among several, and it is rarely the binding one on its own. The full propagation sequence, including where light fits against temperature and timing, is in the seed starting schedule.