How To Choose A Grow Light For Houseplants (Without Getting Scammed)
Aaron DeaconI’ve spent thousands of dollars on grow lights over the years. My first LED setup cost me $2,000—you could buy a similar one today for around $500. Some of that spending was tuition, the expensive kind where you learn what not to buy by buying it.
So let me save you some of that money.
The grow light market is full of numbers designed to confuse you. “600W replacement” on a light that draws 100 watts. Vague “full spectrum” claims. Kelvin ratings with no explanation. Here’s what actually matters—starting with whether you even need a light, and ending with exactly how to run one.
TL;DR – Lighting & Grow Lights For Houseplants
- Light is food for plants. The right spot with good light all day makes a bigger difference than almost anything else.
- Most houseplants want bright indirect light—they evolved under a rainforest canopy, not in an open field.
- Try natural light first. The hand-shadow test and your window direction tell you what you’ve got.
- If you need a grow light, go full-spectrum LED, dimmable, 4000–6000K. Aim for at least 50 actual watts per fixture.
- Ignore “equivalent wattage”—it’s marketing nonsense. Only real power draw counts.
- Keep lights 6–12 inches above foliage. Lower the light before you turn up the power.
- Run times: 16–18 hours a day as a plant’s only light; 6–12 hours if you’re supplementing a window. Use a timer.
Start With The Light You Already Have
Before you buy anything, understand the light in your home. Often the fix isn’t a grow light—it’s moving a plant three feet.
Direct vs indirect light
Think of it like sunbathing. Direct light is the sun’s rays hitting the leaf with nothing in the way—lying out on an open beach. Great for cacti, succulents, some palms and crotons, but tough on almost every other tropical.
Indirect light is bright, but filtered first—imagine sitting under a palm tree on that same beach. The room feels bright, but no harsh beam lands on the leaves. This is what most houseplants want, because most of them evolved on a rainforest floor under a canopy.
One helpful quirk of growing indoors: house windows block around 99% of the UV in sunlight, and UV is what really burns and stresses plants outdoors. So you get more wiggle room inside than you’d expect.
The hand-shadow test
Hold your hand a few inches above a leaf and look at the shadow:
- Sharp, crisp shadow = direct light
- Soft, fuzzy shadow = indirect light
- No shadow at all = low light—find a brighter spot
Plenty of plants survive in low light, but they don’t make real progress. Surviving and thriving are different things.
Ranking your windows
Windows are ranked by the direction they face (northern hemisphere):
- South-facing: the brightest, most intense light all day. Sun-lovers go right at the glass; everything else sits a bit back or behind larger plants for filtered light.
- East-facing: gentle morning sun, then bright indirect the rest of the day. The easiest, most forgiving window in the house—great for almost everything.
- West-facing: bright, with hot afternoon sun. Good for many plants, but that late-day light can scorch sensitive leaves right at the glass.
- North-facing: the dimmest. Fine for low-light-tolerant plants (snake plants, pothos, ZZ, peace lilies), but growth and blooming will be slow. Reflected light off white walls or pale floors helps.
Rule of thumb: the further from the window, the less light—fast. Intensity drops off dramatically just a few feet into a room, even when it still looks bright to you (your pupils cheat by adjusting). When in doubt, closer to the window beats the back corner.
The one exception is winter: the sun sits lower in the sky, so brighter light reaches deeper into your home—just for fewer hours than in summer.
Signs A Plant Wants More Light
Your plants will tell you when the natural light isn’t enough:
- Stretched, leggy growth reaching toward the window
- Large gaps between leaves
- Small, pale new leaves
- Loss of variegation
- General slow stalling
If you’ve moved the plant to your best window and still see these, it’s time for a grow light—which is where the rest of this guide comes in.
LED, And Why Nothing Else Really Competes
When I started growing years ago, LED was still expensive and CFL was the practical option. That era is over. Grow lights have come a long way even in the last 8 years—far more powerful, more efficient, and a fraction of the cost.
Full-spectrum LED is what I recommend, always. They’re energy efficient, run cool, last for years, and mimic natural sunlight. They cost more up front than some options, and they’re worth it. Look for one that’s dimmable and rated 4000–6000K (more on what that means below).
The alternatives, honestly compared:
- Fluorescent (T5) tubes – a solid budget option and full-spectrum too. They make more heat per watt, so you can’t get them as close to plants as LED, and you’ll replace the bulbs every 6–12 months (high-output bulbs are about 54 watts each). Weigh the cost of something that lasts years against something you’re constantly re-bulbing. Keep spares on hand.
- Regular household LED or incandescent bulbs – mostly don’t cut it. They’re designed for low wattage (6–10 watts) and don’t support real growth. Don’t rely on them.
The Wattage Scam (Read This Before You Buy)
This is where most people get taken, so I’ll be blunt.
You’ll see listings shouting “600W!” on a light that actually draws about 100 watts from the wall. That 600 is an “equivalent” or “replacement” figure—a marketing invention with no standard behind it. On Amazon especially, these numbers are honestly bullshit, and they’re designed to fool you.
Find the actual power draw—the real wattage the fixture consumes—and judge on that. It’s usually buried in the specs precisely because it’s smaller than the headline. If a seller hides it, that tells you what you need to know about the seller.
As a floor, aim for a minimum of 50 actual watts per fixture. Larger, higher-wattage fixtures cover more plants—for scale, my 400-watt LEDs were more than enough to grow and flower cannabis in an 8ft × 8ft space, and houseplants need significantly less light than that.
How Much Light, And What’s This “Kelvin” Number?
Real wattage, full-spectrum LED:
- Houseplants: around 50 actual watts grows gorgeous foliage plants year-round. They evolved in shade and don’t want blazing intensity.
- Fast growers (cannabis, fruit, veg): 100–200 actual watts minimum—these photosynthesize hard and need genuine intensity.
- Seedlings: bright light, kept close. Insufficient light is the number-one cause of leggy, stretched seedlings.
Kelvin (K) — the “colour temperature” of light
Kelvin measures the colour of light, not its heat. It’s worth understanding because it’s printed on every bulb:
- Higher Kelvin (bluer light, ~6000K) is great for vegetative growth—it mimics bright spring sun.
- Lower Kelvin (redder light, ~3000–4000K) favours flowering—it mimics fall sun.
For general houseplant growing, a 4000–6000K full-spectrum light covers you nicely. This is also why “full spectrum” matters: plants use a range of wavelengths for different processes, so a smooth, complete spectrum supports the whole plant rather than just driving raw photosynthesis—and it looks like natural white light in your home, instead of the purple “blurple” glow of red/blue-only lights.
Low Kelvins = red/warm light | High Kelvins = blue/bright light
Blue = vegetative growth / spring sun | Red = flowering / fall sun
A small aside worth appreciating: plants look green because they reflect green light—it’s the part of the spectrum they use least. Makes you realize how little of the world around us we actually sense.
How Far Away? The Cloud-And-Rain Trick
Keep your light 6–12 inches above the foliage. Too close can bleach or scorch leaves (yes, even cool-running LEDs); too far and the intensity drops off so steeply the plant barely benefits.
Here’s the mental model that finally made this click for me. You’ll see PPFD in grow light specs (Photosynthetic Photon Flux Density)—don’t let the word scare you.
Imagine your grow light is a cloud, and the light it puts out is rain. The closer the cloud is to your plant, the more rain lands directly on it, and the more intense it is. Raise the cloud and the same rain spreads over a bigger area, so it’s gentler on any one plant.
So the practical rule: if your plants are stretching toward the light, lower the light before you turn up the power (or buy a stronger one). Make the rain more direct before you spend more on electricity. And because a higher light covers more area, that’s how you light more plants at once—you just need a more powerful “cloud.”
How Long To Run Your Lights
It depends on whether the grow light is the plant’s only light or a top-up:
- Little or no natural light (grow light is the sole source): run it 16–18 hours a day.
- Supplementing a window: 6–12 hours a day is plenty.
Get a light timer. Seriously—they’re the key to the whole thing. Consistency matters more than you’d think, and a timer removes the daily decision. A single good light on a timer can turn a dark apartment corner into a happy little jungle. 🌿
Leaf Burn: What To Watch For
Too much intense light—from a window or a grow light hung too close—cooks the tissue. It’s worth recognizing:
What it looks like:
- Crispy, dry, bleached or brown patches, usually on the side facing the light
- Faded, washed-out or yellowing colour on the sun-side
- Dry, papery spots—distinct from overwatering damage, which is soft and mushy (more on telling those apart in our overwatering vs root rot guide)
How to avoid it:
- Move sensitive plants further from the window, or raise the grow light
- Never move a plant from a dim spot into full sun overnight—acclimate it gradually
- Watch south and west windows in summer, when the sun is strongest
- Rotate plants now and then for even growth, so they don’t end up leaning back like Fat Joe
Hardening Plants Off For Outdoors
Moving a plant straight outside full-time is a great way to fry it—outdoor sun is way stronger than the brightest windowsill, plus there’s wind and temperature swings. “Hardening off” just means easing them into it over about 7 to 14 days:
- Days 1–2: 1–2 hours outside in full shade or dappled light, then back in.
- Days 3–5: build up to 3–4 hours, adding a little gentle morning sun.
- Days 6–9: work up to half a day, introducing more direct sun (morning is safest).
- Days 10–14: full days outside, then finally overnight once nights are warm.
Go slower for tender, thin-leaved plants, and always start in gentle morning sun. If leaves look pale or crispy, back off a step—rushing it sets you back 2–3 weeks while the plant recovers from the stress. (When you bring them back in for winter, it’s worth a pest clean-up first—see our diatomaceous earth guide.)
Light Is Only One Input
A grow light fixes a light shortage. It doesn’t fix anything else—and this trips people up.
More light means the plant photosynthesizes more, which means it needs more of everything else to keep up: water, nutrients, and a healthy root system to deliver them. Add intense light to a plant that’s already stressed by poor soil or chronic overwatering and you can make things worse, because you’re asking it to work harder than it can.
So a grow light works best as part of a whole:
- The right soil for the plant
- Correct watering for its new, faster growth rate
- Gentle, steady natural nutrition to match the increased demand
Mistakes That Waste Your Money
1. Buying a light before checking your windows
Sometimes the fix is moving the plant to a better window, not buying anything. Read your light first.
2. Buying on “equivalent wattage”
The headline number is marketing. Find the real draw or walk away.
3. Hanging it too far away
Intensity falls off fast with distance. Lower the light before you turn up the power—remember the cloud and rain.
4. Running it 24/7
Plants need a dark period too. Round-the-clock light stresses them and wastes power. Use a timer.
5. Relying on household bulbs
A 6–10 watt lamp bulb won’t grow a plant. You need a real full-spectrum grow light.
6. Expecting light to fix a non-light problem
If the real issue is soil, water or roots, a grow light won’t solve it—and may add stress.
Grow Light & Lighting FAQ
What kind of grow light is best for houseplants?
A full-spectrum LED—dimmable, 4000–6000K, at least 50 actual watts. It’s efficient, runs cool, lasts for years, and delivers a natural-looking complete spectrum. T5 fluorescent tubes are a solid budget alternative but need bulb replacements every 6–12 months.
What’s the difference between direct and indirect light?
Direct light hits the leaf with nothing in the way, like an open beach—good for cacti, succulents and other sun-lovers. Indirect light is bright but filtered, like sitting under a palm tree, and it’s what most houseplants want. Use the hand-shadow test: a crisp shadow means direct, a fuzzy shadow means indirect.
How many watts do houseplants need?
Roughly 50 actual watts of full-spectrum LED per fixture grows beautiful foliage houseplants. Fast growers like cannabis or vegetables need 100–200 actual watts minimum. Always go by real power draw, not “equivalent” marketing figures.
What does the Kelvin (K) number mean on a grow light?
Kelvin is the colour of the light, not its heat. Higher Kelvin (~6000K) is bluer and favours leafy vegetative growth; lower Kelvin (~3000–4000K) is redder and favours flowering. For general houseplant growing, 4000–6000K full-spectrum is ideal.
How close should a grow light be to plants?
About 6–12 inches above the foliage. Think of the light as a cloud and its output as rain: the closer it is, the more intense the light on the plant. If plants stretch toward it, lower the light before turning up the power.
How long should I run a grow light?
16–18 hours a day if it’s the plant’s only light source, or 6–12 hours if you’re supplementing natural window light. Plants need a dark period, so don’t run lights 24/7—and use a timer for consistency.
Are cheap Amazon grow lights any good?
Some are fine, but the category is full of dishonest wattage claims—a “600W” light often draws only 100 real watts. Ignore the headline number, find the actual power draw in the specs, and judge on that.
Can grow lights burn plants?
Yes. Even though LEDs run cool, a powerful light too close can bleach or scorch leaves. If leaves directly under the light go pale, patchy or crispy while the rest look fine, raise the fixture.
Why are my seedlings leggy and stretched?
Almost always insufficient light. Seedlings need bright light kept close, or they stretch reaching for it. A full-spectrum LED positioned near them keeps growth compact—it won’t un-stretch existing growth, but new growth will be sturdy.
Bringing It Back To Your Shelf
Light is food. Start by reading the light you already have—the hand-shadow test and your window direction tell you most of what you need—and move plants before you spend a cent.
When a plant genuinely needs more, refuse to be fooled: ignore the equivalent-wattage theatre, pick a dimmable full-spectrum LED at 4000–6000K and at least 50 real watts, hang it 6–12 inches up, and put it on a timer for 16–18 hours (or 6–12 if you’re topping up a window). Remember the cloud and the rain, and lower the light before you crank the power.
And keep it in perspective—light gives a plant the energy to grow, but soil, water and nutrition decide whether it can use that energy. Get those working together and a modest light turns a dark corner into a jungle. You don’t need the most expensive light on the shelf. You need an honest one, sized right and run sensibly—which costs a lot less than the $2,000 I spent learning that.
Terms & Abbreviations (Quick Reference)
- Direct light – Sunlight hitting the leaf unobstructed. Suits cacti, succulents and other sun-lovers.
- Indirect light – Bright but filtered light, what most houseplants prefer.
- LED – Light Emitting Diode. The efficient, cool-running, long-lived standard for grow lights.
- Full spectrum – Light delivering a complete range of colour mimicking sunlight, rather than just blue and red.
- Kelvin (K) – The colour temperature of light. Higher = bluer (vegetative growth); lower = redder (flowering).
- Actual wattage – The real power a light draws from the wall. The number that matters—unlike “equivalent” wattage.
- T5 – A type of full-spectrum fluorescent tube. Budget-friendly but needs regular bulb replacement.
- PPFD – Photosynthetic Photon Flux Density; how much usable light actually reaches the plant. Closer light = higher PPFD.
- Hardening off – Gradually acclimating a plant to stronger light (usually outdoors) over 7–14 days to prevent burn.
- Leaf burn – Dry, bleached or brown patches from more intense light than a plant is adapted to.
- Leggy – Stretched, weak growth with long gaps between leaves, caused by insufficient light.