For LED strip lights the T5 and T8 designations are largely a hangover from fluorescent tube diameters and tell you almost nothing about output. Compare actual wattage, strip length and the light delivered at plant height instead. In practice T8 strips at 2 ft suit standard 24 in wire shelving, and 4 ft T5 strips suit longer benches, and either can be doubled up where one strip leaves the tray edges leggy.
What T5 and T8 mean
Tube diameter, not brightness
Typical strip
About 20 W for 4 ft
Seedling target
Roughly 200 to 400 PPFD
Hanging height
Inches, not feet, for seedlings
Researched from published specifications and verified owner reviews · Updated 2026-08-16
The T numbers come from fluorescent tubes, where T5 meant five eighths of an inch across and T8 meant one inch. Those diameters mattered when the tube was the light source. On an LED strip the designation has been carried over as a product naming convention and does not reliably tell you how much light comes out.
So the useful comparison is not T5 against T8. It is watts, length, and the distance you can hang the fixture from the leaves.
The comparison
Figure 1. What actually differs between strip options·7 rows
Figure 1. What actually differs between strip options
Measure
4 ft strips
2 ft strips
Suits 48 in benching
Yes
Two per shelf
Suits 24 in wire shelving
Overhangs
Yes
Typical draw per strip
About 20 W
About 10 W
Strips needed per tray width
One to two
One to two
Linkable end to end
Usually
Usually
Cost per lit foot
Lower
Higher
Hanging height for seedlings
A few inches above the canopy
A few inches above the canopy
Researched general information rather than professional advice. Confirm wattage and dimensions before buying.
Match the strip to the shelf, not to the label
Most home seed-starting racks are built from 24 inch wire shelving, and a Barrina T8 2 ft Grow Lights, 5000 K, 6-Pack ($71.24) fits that exactly with no overhang and no wasted light off the ends. A longer bench or a run of 1020 trays down a greenhouse staging is better served by Barrina 4 ft LED Grow Lights, 5000 K, 6-Pack ($94.99), which cost less per lit foot.
Where a single strip per shelf leaves the outer rows of a tray stretching toward the middle, the answer is a second strip rather than a different strip. An Barrina T5 4 ft Grow Lights, 160 W Total, 8-Pack ($80.99) gives enough to double up across three or four shelves, and doubling up is the single most effective fix for leggy seedlings on a rack.
Height matters more than the fixture
Light falls away sharply with distance. A strip that produces adequate light two inches above the canopy produces a fraction of that a foot away, which is why the same fixture can be described as excellent by one grower and useless by another. Hang strips on adjustable OneChoi Adjustable Rope Light Hangers, 8 ft ($35.00) and raise them as the seedlings grow, keeping them close.
The number that describes this properly is PPFD, and seedlings generally want somewhere in the region of 200 to 400 micromoles per square metre per second for a 14 to 16 hour day. Work out the daily light integral for your crop with the DLI and PPFD calculator rather than guessing from wattage.
Note
Colour temperature is not the deciding factor
Full-spectrum white strips at around 5000 K grow seedlings perfectly well and are far more pleasant to work under than the pink and purple fixtures. Plants use a broad range of the spectrum, and for seed starting the total quantity of light reaching the leaf matters much more than its exact colour.
The decision, summarised
Standard 24 in wire shelving: 2 ft strips, one or two per shelf.
Greenhouse staging or a long bench: 4 ft strips, cheaper per lit foot.
Seedlings stretching at the tray edges: add a second strip rather than raising the first.
No rack yet and no desire to wire one: a stand with lights already fitted.
Unsure whether the light is adequate: measure PPFD rather than comparing wattages on a listing.
Strips by bench length
The same product family in the three lengths and quantities that cover most home setups.
On fluorescent tubes T5 high-output lamps generally were brighter per foot. On LED strips the designation is mostly a naming convention inherited from those tubes and does not reliably indicate output. Compare the stated wattage and the length instead, and if the listing does not state wattage clearly, treat that as a reason to look elsewhere.
+- How close should grow lights be to seedlings?
For low-wattage LED strips over seedlings, a few inches above the canopy, raised as the plants grow. Light intensity falls off quickly with distance, so a strip hung a foot away is doing a fraction of the work it could. Watch the plants: stretching means more light or closer light, while bleached or bronzed leaf tips mean too close.
+- How many hours should the lights run?
Fourteen to sixteen hours a day suits most seedlings, on a timer so it is consistent. Longer is not automatically better and most crops want a dark period. The figure worth targeting is the daily light integral for the crop, which combines intensity and duration, and the DLI calculator turns your fixture and hours into that number.
+- Do I need grow lights at all in a greenhouse?
For seed starting in late winter and early spring, usually yes, because natural day length and intensity at that time of year are the limiting factor and greenhouse glazing removes some of what is left. Later in the season supplementary light adds little. The exception is propagation benches in a shaded corner, where light is short regardless of the calendar.
Working out the figures for your own house and season? The Greenhouse Build & Growing Planner is the
paid version of these pages: 8 printable worksheets you fill in with your own
numbers, plus the full PDF, $29.
