Lighting

Even with your nutrients and climate dialled in, the light is usually the real ceiling on yield. Indoors you are the sun, and a plant can only build what the light lets it. LED is the modern default, but a light is only right when its spectrum, intensity and coverage are matched to the space and the grow stage. This guide shows you how to size a light properly, then buy the fixture that fits.

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Grow lights & accessories we carry

The light types and where each one fits

There is no single best grow light, only the right tool for your space, stage and budget. Four families cover almost everything you will meet.

LED is the modern default and what most new grows should buy. Good fixtures are the most efficient light you can hang, they run cooler than the alternatives, they last for years and many are dimmable and full-spectrum out of the box. The trade is a higher price up front, which the running-cost saving pays back over time. We stock LED across the range, from high-output bar fixtures like the Gavita Pro 1700e, Gavita RS 1900e and PHOTOBIO CX for serious flowering rooms, through the Fluence SPYDR with its broad PhysioSpec spectrum, down to small propagation lamps like the Agrobrite standing LED for a few plants on a bench.

HID (high-intensity discharge) is the old workhorse and still a fair choice on a tight budget, because the fixtures are cheap even if they cost more to run. HID splits into two bulbs. Metal halide (MH) runs blue-rich and suits vegetative growth. High-pressure sodium (HPS) runs red-rich and is a proven flowering light. The step up is double-ended (DE) HPS, such as the Gavita Pro DE or an Eye-Hortilux DE lamp, which is brighter and holds output better over its life than an old single-ended bulb. HID needs a ballast, a reflector and real heat management.

CMH / LEC (ceramic metal halide, also called light-emitting ceramic) sits between the two. It gives a broad, natural full-spectrum output with useful ultraviolet, excellent color rendering and strong efficiency for a bulb technology. The common 315W CMH, running a lamp like the Philips Master Color CDM 315W 3100K, is a favorite for small flowering spaces and for growers who want quality and terpene development from a single fixture.

T5 and fluorescent are the gentle end, and they are made for propagation. Seedlings, clones and mother plants want low, soft, cool light close over the canopy, which is exactly what a SunBlaster T5HO strip or an Agrobrite T5 bank delivers. They run cool enough to sit an inch or two away without scorching a fresh cutting, and they sip power. They are not flowering lights, and that is the point. Match the tool to the job.

Grow light types at a glance

Type	Efficiency (µmol/J)	Spectrum	Best stage	Heat & running cost
LED	Highest, ~2.5–3.0+	Full-spectrum, often tuneable	Whole grow, seed to harvest	Low heat, lowest to run
CMH / LEC	Good for a bulb, ~1.9	Broad full-spectrum, some UV	All stages; small flower rooms	Moderate heat and cost
HPS (incl. DE)	~1.7 (DE holds better)	Red-rich	Flowering	High heat, higher to run
MH	~1.3–1.7	Blue-rich	Vegetative	High heat, higher to run
T5 / fluorescent	Lower, ~1.0	Cool or warm white options	Propagation, clones, mothers	Very low heat and cost

Electrical safety

Grow lights draw serious, continuous power. Keep the total draw of lights, ballasts and controllers within your circuit's rating — high-wattage fixtures deserve a dedicated circuit — and use timers and controllers rated for the connected load. Keep drivers and ballasts ventilated, mounted clear of water lines and reservoirs, and put drip loops in cords near any water. For wiring beyond plug-in equipment, use a licensed electrician and follow local code. Always follow each fixture's manual — ratings and clearances differ per product; see each product page for its specifics.

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Lighting buying guide

Why the light is your real yield ceiling

Indoors, your light replaces the sun, and the plant cannot grow faster than the light allows. You can perfect your feed and your environment and still fall short, because photosynthesis is the engine and light is the fuel. This is the part of the grow most people underbuy, and it is the one part you cannot fix later with an additive.

Photosynthesis is simple to state. Leaves capture light energy and use it, with water and carbon dioxide, to build the sugars that become stems, leaves and flowers. More usable light, up to the plant’s ceiling, means more sugar and more yield. That word usable matters. Plants do not respond to light the way your eyes do.

Here is the single most useful thing to understand before you spend a penny. Brightness to the human eye is the wrong measure. Your eye is tuned to green and yellow light, which is exactly the part of the spectrum a leaf reflects and uses least. A light can look blindingly bright and still be feeding your plants poorly, or look a dull purple and be pushing them hard. Lux and lumens measure light for human vision, so ignore them on a grow light. What you care about is the number of photons in the range plants actually photosynthesize with, and that has its own set of units we cover further down. Buy on those, not on how bright the fixture looks in the shop.

There is a ceiling worth knowing about too. A plant can only use so much light before other things become the limit, at which point more intensity stops adding growth and starts causing harm. In normal air that ceiling is lower than you might think, because carbon dioxide runs out before the leaf does. Growers who enrich their room with CO₂ can push their plants to use far more light, which is why commercial rooms chase such high intensity. For a typical tent or small room without CO₂, there is no prize for overpowering the space. Buy enough light to hit the intensity your stage wants, and put the rest of your budget into control and environment.

Spectrum: the color of light and why it shifts by stage

Spectrum is the mix of colors in your light, and plants use different colors for different jobs. In the wild the sun changes through the day and the season; indoors you either choose a fixed spectrum that does most jobs well or you steer it as the plant develops.

Two bands do most of the heavy lifting. Blue light (around 400 to 500 nanometers) keeps growth tight and compact, drives strong vegetative structure and thick leaves, and is what a plant wants while it builds its frame. Red light (around 620 to 700 nm) is the most efficient part of the spectrum for photosynthesis and is the main driver of flowering and fruit. This is the plain reason MH (blue-rich) was traditionally used for veg and HPS (red-rich) for flower.

Full-spectrum lights, which most quality LED and all CMH fixtures are, blend blue, green, red and a slug of white so a single fixture carries a plant from seedling to harvest without a bulb change. Green light, long dismissed, is now known to penetrate deeper into the canopy than red or blue, so it is not wasted. Far-red (around 700 to 780 nm) works with red to trigger flowering responses and can speed the shade-avoidance stretch, which some growers use deliberately at flip. A little ultraviolet (UV) can thicken leaves and push the plant to produce more protective compounds, which in aromatic crops can mean more resin and stronger aroma. UV is a small dose tool, not a headline, and CMH lamps and dedicated units like the Gavita UVR LED supply it in controlled amounts.

The practical takeaway: for one fixture across the whole grow, buy a genuine full-spectrum light and stop worrying about the color. If you want to steer, lean bluer in veg and richer in red toward flower, and treat far-red and UV as fine-tuning once the basics are right.

The metrics that actually matter: PAR, PPF, PPFD and efficacy

This is the vocabulary that separates a good buying decision from a guess. Four numbers matter, and once you can read them the marketing falls away.

• PAR (photosynthetically active radiation) is not a number, it is a range. It is the band of light, roughly 400 to 700 nm, that plants use to photosynthesize. Everything below is a measurement of light within that band.
• PPF (photosynthetic photon flux) is the total amount of usable light a fixture makes, measured in micromoles per second (µmol/s). It tells you how much PAR light the whole fixture pumps out, but not where it lands.
• PPFD (photosynthetic photon flux density) is the number that grows your plants. It is how much PAR light actually lands on the canopy, measured in micromoles per square meter per second (µmol/m²/s) at a set distance. Two fixtures with the same PPF can give very different PPFD depending on how well they spread light over your area. This is the figure you size a light and set a hanging height by.
• Efficacy (µmol/J) is how much usable light you get per unit of electricity, in micromoles per joule (per watt of draw). It is the efficiency figure and it decides your running cost. Higher is better.

Which do you buy on? Efficacy first, then PPF. A high µmol/J number means the fixture turns your electricity into plant light rather than heat and waste, which matters every single day it runs. Then check PPF is enough for your area. PPFD you set yourself with hanging height once the light is up. Treat µmol/J as the headline spec, the way you would read miles per gallon on a car, and be wary of any light that hides it.

One caution on comparing numbers. Only compare like with like: a PPF figure means little without knowing the fixture’s true power draw, and a PPFD figure is meaningless without the distance and the area it was measured over. A dishonest spec sheet quotes PPFD at an unrealistically close distance or over a tiny central patch to flatter the number. The brands we carry, such as Gavita and Fluence, publish full PPFD maps across a stated coverage area at set heights, which is exactly the honesty you want to see before you spend.

Sizing the light: wattage per area and target PPFD by stage

Sizing is where most grows go wrong in both directions. Underbuy and you get loose, airy, low-weight results. Overbuy and you bleach the canopy and waste money on power. Get it right and everything else you do actually pays off.

Start with a rough wattage rule as a sanity check, then refine with PPFD. For efficient modern LED, plan on roughly 25 to 40 watts of real draw per square foot of canopy, which puts a standard 4ft by 4ft tent at around 500 to 650 watts of quality LED for a full flowering load. Old-style HID needs more like 40 to 60 watts per square foot because so much of it becomes heat. Watch the words real draw. A great many LED lights are sold on an inflated wattage that is nowhere near what they pull at the wall, so read the actual power figure, not the model name.

Wattage gets you in the right area; PPFD by stage gets you dialled in. Young plants want gentle light and mature flowering plants want a lot, and pushing full intensity onto a seedling is a common and costly mistake. The bands below are sound starting points for most crops in normal air; growers adding CO₂ can push the top end higher.

Target PPFD and LED hanging height by growth stage

Stage	Target PPFD (µmol/m²/s)	Approx. LED hang height	Notes
Seedling / clone	100–300	24–36 in	Soft light; dim the fixture or raise it
Early veg	300–450	20–28 in	Ramp up as the plant fills out
Late veg	400–600	18–24 in	Build frame before the flip
Flower	600–900	12–18 in	Push hardest here; 1000+ only with CO2

Use a PAR meter if you want to be exact, or follow the fixture maker’s own PPFD map, which good brands like Gavita and Fluence publish for each model at set heights. The distances above are a starting frame for LED; always cross-check the maker’s chart, because a 250W bar and an 850W panel do not hang at the same height.

Hanging distance: too close bleaches, too far stretches

Hanging height is the free dial that sets your PPFD, and it is worth getting right because both mistakes cost you yield. Hang the light too far away and the plants stretch, reaching for it with long weak internodes, thin stems and loose flowers. Hang it too close and you overload the top of the canopy: the tops bleach to a pale, yellow-white, the leaves closest to the light curl and taco, and in severe cases you get light burn that no feed will fix.

The rule follows the plant. Seedlings and clones sit furthest away because they cannot use much light and burn easily, so keep an LED well back, in the region of 24 to 36 in, or use a gentle T5 close over them instead. As the plant vegetates and its demand climbs, bring the light down stage by stage. Through flower, a strong LED typically runs closest, often around 12 to 18 in above the canopy, though the exact figure depends entirely on the fixture’s power and its published chart.

Two habits keep you safe. First, watch the plant, not just the tape measure: praying leaves reaching up happily mean the height is good, while bleached tops or leaves folding away from the light mean raise it now. Second, if your fixture dims, use the dimmer to control intensity and keep the light at a sensible height rather than yo-yoing it up and down. A dimmable LED lets you deliver a seedling-safe PPFD from a flowering-height fixture, which is one of the quiet advantages of buying good LED.

Heat, efficiency and what a light really costs to run

Every watt a light draws that does not become usable light becomes heat, and heat is the hidden cost that shapes your whole room. This matters even more over water. Hydroponic systems and reservoirs already add humidity, and a hot HID lamp above them drives temperatures and vapor up further, stressing roots, feeding mold risk and forcing you to spend on extraction and cooling to compensate. Cooler-running LED and CMH make the whole environment easier to hold steady, which is a real reason they have taken over.

Efficiency is not an abstract virtue here; it is money. A more efficient light (higher µmol/J) gives you the same canopy light for fewer watts, which cuts both your electricity bill and your cooling load at the same time. With US electricity averaging roughly 15 to 20 cents per kWh, and higher in states like California, the running cost is a serious line in any grow budget, and it is worth a moment of arithmetic before you buy.

The sum is easy. Take the fixture’s real wattage, multiply by hours per day, and divide by 1000 to get kWh per day. A 600W light on an 18-hour veg photoperiod draws 10.8 kWh a day, about $2 a day at 18 cents per kWh. The same light on a 12-hour flower cycle draws 7.2 kWh, about $1.30 a day, which is roughly $80 across a two-month flower. A more efficient fixture doing the same canopy job for 450W instead of 600W saves you a quarter of that, every cycle, for the life of the light. That saving is exactly how a pricier LED pays back its higher sticker over time. When you compare fixtures, compare the running cost, not just the shelf price.

The heat your lights throw is really a climate question. Our Climate & Environment guide covers sizing the ventilation and cooling that keep a hot canopy in range.

Buying LED without getting burned: diodes, driver, lifespan and honest wattage

LED is the right default, but the market is full of cheap panels dressed up with big claims, so it pays to know what separates a fixture worth years of your electricity from a disposable one. The gap between a good LED and a bad one is far wider than the price tag suggests.

Diodes. The light-emitting diodes are the engine. Reputable fixtures use known, well-binned diodes from established makers and run them within their limits so they hold output and color for years. Bargain lights overdrive cheap diodes, which fade and shift fast. The driver is the power supply, and it is the part that most often fails first. A quality driver, from a name like the ones behind our Gavita, Fluence and PHOTOBIO fixtures, runs cooler, dims cleanly and simply lasts. Build and cooling matter too: a solid heatsink or a well-designed passive bar keeps the diodes cool, and cool diodes live longer and stay efficient.

Lifespan and warranty. LED does not usually die in a flash, it dims slowly, so makers rate life by how long until output drops to a set fraction of new. A meaningful warranty from a serious brand is your best proxy for real quality, because a company only backs a fixture for years if it expects it to last them. Read what the warranty actually covers, and favor brands that stand behind the driver as well as the diodes.

Honest wattage. This is the single biggest trap. A light sold as a huge wattage in its name but drawing a fraction of that at the wall is the classic budget-LED con. Always find the real power draw and the µmol/J efficacy figure, and size your grow on those. If a fixture will not tell you its true wattage and its efficacy, that silence is the answer. The brands we carry publish both because they can stand behind them.

Timers, controls, light movers and mounting it safely

The fixture is most of the job, but a handful of accessories decide whether your light runs reliably, evenly and safely. None of them are optional in a real grow.

Timers and photoperiod control. Your light schedule triggers flowering, so it has to be exact and it has to be reliable. Long veg photoperiods flip to a strict 12 hours on and 12 hours off to bring most plants into flower, and even a single missed or interrupted dark period can stress a crop or cause it to revert. A dependable timer is a non-negotiable, and larger rooms are better served by a proper lighting controller that switches everything together and, on compatible fixtures, ramps the light up and down like a sunrise and sunset.

Dimming and automation. A dimmable fixture is one of the best reasons to buy quality LED, because it lets one light serve gently through propagation and hard through flower without ever moving it. Many modern fixtures, including the Gavita e-series and the PHOTOBIO range, accept an external dimmer or controller so you can set intensity precisely and even link output to your environment. That control is how you deliver the PPFD bands in the sizing table without touching the hanger.

Light movers. A motorized rail such as the LightRail slowly tracks the fixture back and forth over the canopy. That single moving light does the work of covering more area, eliminates the fixed shadows and hot spots you get from a static light, and lets the same fixture penetrate the canopy from changing angles. In the right room a mover meaningfully lifts even coverage and yield from the light you already own.

Mounting. Grow lights are heavy and they hang over your plants, your reservoir and your electrics, so mount them properly. A pair of ratchet hangers is the standard, and for good reason: they take the weight securely, they let you level a fixture in seconds, and they make the small, tool-free height adjustments the stages above call for effortless. Rig every fixture on rated hangers from a secure point. It is the cheapest insurance in the room.

Two more items round out a bulb-based setup. If you run HID or CMH, the ballast or driver is the box that powers and regulates the lamp, and a good modern electronic one runs the bulb efficiently, often lets you switch wattage, and is far kinder than the old magnetic kind. The reflector or hood then aims the light down onto the canopy instead of letting it scatter into the walls, so a well-shaped reflector genuinely lifts your usable PPFD from the same bulb. LED bar fixtures build both of these in, which is part of why they are so simple to run: no separate ballast, no reflector to buy, just hang, dim and go.

Frequently asked questions

Is this what you need?

• A good fit if you grow where sunlight can't reach or can't be trusted — tents, basements, winter rooms — or you're replacing a worn HID setup.
• Not the fix for stretching plants when the real cause is hanging height or coverage — adjust placement before buying more wattage.
• Not the fix for a hot room: heat problems are ventilation problems (see Climate & Environment), and a bigger light makes them worse.
• Skip the upgrade if a windowsill herb pot is the whole grow — horticultural lighting pays off only when light is genuinely the limit.