LED Grow Lights: The Complete UK Buyer's Guide (2026)

The number that actually tells you how well an LED grow light will perform is its PPF (total light output, measured in μmol/s) alongside its efficacy (μmol/J), not the wattage printed on the box. Two lights can both say "720W" and produce very different amounts of usable light for your plants. Below we explain what the specs actually mean, how full spectrum and quantum board designs differ from the bar-style fixtures most UK growers use, and which real, in-stock LED grow lights at DiscountHydro suit a budget setup, a standard 1.2m tent, or a larger grow room.

In This Article

• What do PAR, PPF, PPFD and μmol/J actually mean?
• Full spectrum, quantum board or bar-style: what's the difference?
• How do you size an LED grow light to your tent?
• Best LED grow lights at DiscountHydro for 2026
• Comparison table
• Installation tips and common mistakes
• Frequently asked questions

What Do PAR, PPF, PPFD and μmol/J Actually Mean?

PAR (Photosynthetically Active Radiation) is the band of light wavelengths plants actually use for photosynthesis. PPF (Photosynthetic Photon Flux) measures the total amount of that light a fixture produces every second, in micromoles per second (μmol/s), regardless of where it lands. PPFD (Photosynthetic Photon Flux Density) measures how much of that light actually reaches a specific point on your canopy, which is why the same fixture gives a higher PPFD reading directly underneath it than at the edges of your tent.

Efficacy, measured in μmol/J, tells you how much usable light a fixture produces per watt of electricity it draws. A 720W-rated light with 3.2 μmol/J efficacy is genuinely more efficient, and usually produces more usable light, than a 720W light rated at 2.7 μmol/J, even though the wattage label is identical. When comparing lights, always check PPF and efficacy on the spec sheet rather than relying on wattage alone.

Full Spectrum, Quantum Board or Bar-Style: What's the Difference?

Full spectrum simply means a fixture outputs light across most of the visible spectrum, roughly mimicking natural sunlight, rather than the narrow blue-and-red "blurple" spectrum of older LED designs. Nearly every modern LED grow light sold today, including every fixture in this guide, is full spectrum.

Quantum board and bar-style refer to the physical layout of the LEDs, not the light quality. A quantum board is a single flat panel densely packed with diodes. A bar-style fixture, which is what most of DiscountHydro's range uses, spreads the diodes across several parallel bars connected by a frame, usually foldable for easier shipping and mounting. Bar-style fixtures generally give more even canopy coverage for the same footprint and are easier to hang and adjust, which is why they dominate the mid-range market. Neither design is inherently better; what matters for your plants is the PPF and efficacy figures, not which physical layout produced them.

How Do You Size an LED Grow Light to Your Tent?

Match the fixture's manufacturer-rated coverage area to your actual tent footprint rather than assuming a bigger wattage number automatically covers a bigger space. For a full breakdown of which wattage and PPF suit a small propagation space through to a large 1.4m-plus tent, see our dedicated tent-by-tent LED sizing guide.

Best LED Grow Lights at DiscountHydro for 2026

The five fixtures below cover budget through to premium picks, all verified in stock. Full specs and the comparison table further down let you match the right one to your tent.

A premium pick from a well-established UK lighting brand, the Maxibright Varidrive 3 720W 3.0 (£149.00) offers the same 2160 μmol/s PPF at 3.0 μmol/J efficacy in a foldable frame with an integrated driver, built for larger tents and grow rooms running veg through to flowering.

Comparison Table

Fixture	Price	PPF	Efficacy	Rated footprint	Driver
Gorilla LED 720W	£99.99	1944 μmol/s	2.7 μmol/J	1.5m x 1.5m	Built-in
Photon 720W	£109.99	2304 μmol/s	3.2 μmol/J	1.2m x 1.2m	Built-in
Elite Pro 3.0 720W	£129.99	2160 μmol/s	3.0 μmol/J	1.5m x 1.5m	Built-in
Maxibright Varidrive 3	£149.00	2160 μmol/s	3.0 μmol/J	1.5m x 1.5m	Built-in
Omega Infinity 600W	£314.50	1890 μmol/s	3.0 μmol/J	1.4m x 1.4m	Detachable

Installation Tips and Common Mistakes

Hang your light at the distance the manufacturer specifies for your growth stage, usually further away during seedling and early vegetative growth and closer during flowering, and raise it gradually as plants grow rather than leaving it fixed. Use proper ratchet hangers rather than fixed rope so you can adjust height without retying knots. Avoid stretching one fixture across a tent bigger than its rated footprint; coverage drops sharply at the edges, and two smaller lights daisy-chained together will beat one oversized unit for even canopy coverage.

Frequently Asked Questions

Does a higher wattage LED grow light always mean more light for my plants?

No. PPF and efficacy (μmol/J) matter far more than the wattage figure printed on a fixture. Two 720W-class lights in this guide produce noticeably different PPF outputs.

What size LED grow light do I need for a 1.2m x 1.2m tent?

A single 720W-class fixture with a built-in driver, such as the Photon 720W, is the standard choice for the most common home grow tent size in the UK. See our full tent-by-tent sizing guide for other tent sizes.

Is a quantum board LED better than a bar-style fixture?

Neither design is inherently better. Quantum boards and bar-style fixtures are just different physical layouts for the same underlying LED diodes; what determines performance is the PPF and efficacy figures, not the shape of the fixture.

What's the difference between full spectrum and standard LED grow lights?

Full spectrum lights output light across most of the visible spectrum, closer to natural sunlight, while older "blurple" LEDs only emit narrow blue and red bands. Every fixture in this guide is full spectrum.

How much does it cost to run an LED grow light in the UK?

See our dedicated LED running costs guide for a full breakdown by wattage and UK electricity prices.

Can I use two smaller LED grow lights instead of one big one?

Yes, and for tents larger than around 1.4m x 1.4m it's usually the better option. Two daisy-chained fixtures spread light more evenly across the canopy than a single unit pushed beyond its rated footprint.

Are LED grow light strips any good?

LED strips are ideal for small spaces: shelves, propagation trays, windowsill herbs and houseplants. They are not designed to be the main light in a full-size grow tent, where a bar-style fixture or quantum board rated for the footprint will do a much better job. Check the strip's PPF or PPFD figures rather than relying on a wattage claim.

What is under-canopy LED lighting?

Under-canopy lighting means mounting slim LED bars below or alongside the main canopy to light the lower leaves that the top light cannot reach. It is most useful for tall, dense crops such as tomatoes, peppers and cucumbers. It supplements your main light rather than replacing it, so size your overhead fixture first.

Do I need a special LED grow light for a greenhouse?

In a UK greenhouse, LEDs are mainly used to supplement weak winter daylight and extend the day length for overwintering plants, seedlings and winter salads. Because greenhouses are humid and plants get watered, choose a fixture with a good water-resistance rating such as IP65, like the Omega Infinity 600W above, and use outdoor-rated connections.

T5 vs LED: which is better?

T5 fluorescent tubes are cheap to buy and give gentle, even light that suits seedlings and cuttings, but they are less efficient than LEDs and the tubes lose output and usually need replacing about once a year. LEDs cost more upfront but use less electricity for the same light and last many years. For propagation on a budget, T5 is still workable; for anything else, LED is the better long-term choice. Our guide to LED grow lights for seedlings covers propagation lighting in more detail.

How long do LED grow lights last?

Most quality LED grow lights are rated for around 30,000 to 50,000 hours, often quoted as L70 or L90, which is the number of hours before light output falls to 70% or 90% of new. At 12 to 18 hours a day, that is many years of use. The driver usually fails before the diodes do, so a light with a replaceable or detachable driver and a solid warranty lasts longest. Replace or repair a light when output has dropped noticeably, individual diodes or bars fail, or the driver starts to buzz or flicker.