If there's one question every new aquarium enthusiast asks, it's: "How much light do my plants need?" I'll admit: my first aquarium once ran 14 hours a day under spotlights—it was like a sunbed for fish. The result? No tropical plant oasis, but a whopping cloud of algae. The moral of the story: aquarium plants aren't sunbathers. They prefer regularity and the right amount of light. Fortunately, it's not that bad if you know what to look for.
Most aquariums thrive with around 8 hours of light per day. Low-light plants require 15–25 lumens per liter (0.25 W/L) or a PAR value of 75–100 µmol/m²/s. Medium-light plants thrive at 25–50 lumens per liter (~0.5 W/L) or a PAR of ~150. High-light plants require 50+ lumens per liter (~0.8 W/L) and a PAR of 200+. Always use a timer and choose a full-spectrum LED with a high red content (±50%) and a small amount of blue (up to 15%). 
Why is lighting important for aquarium plants?
Light is to plants what pizza is to students: pure energy. Without light, there's no photosynthesis, and without photosynthesis, there's no growth. But there's more to it than just "light on = happy plant."
- Lumen: This is the amount of visible light your lamp produces. It's useful to know, but it doesn't tell you everything about its usefulness for plants.
- Watts per liter: an older way of estimating light intensity. Nowadays, LEDs are much more efficient, so lumens and PAR are more reliable.
- PAR (Photosynthetically Active Radiation): This is the portion of light (400–700 nm) that plants actually use for photosynthesis. Think of PAR as the "edible calories" of light. You can have a lot of lumens, but if the spectrum is wrong, plants won't do much with it.
- Spectrum: Red light (approximately 50%) stimulates growth and flowering, while blue (up to 15%) promotes compact growth. Green is for ornamental purposes, making the plants visibly beautiful to the eye.
And then there's the light duration : 8 hours is ideal for most tanks. Longer light often leads to algae growth because you're running your setup at full speed, while shorter light hours don't give plants enough energy and growth. 👉 Want to read more? Check out plants with low light or our "losing leaves" guide . 
How do you arrange the right lighting step by step?
- Choose your plants: are they easy beginner plants ( Anubias , Java fern ), or plants with high light requirements like Alternanthera sessilis , Rotala orange juice , and Monte Carlo ? 👉 Just starting out? Also check out aquarium plants for beginners .
- Check the intensity: adjust the lumens or PAR value to your plant choice or calculate your wattage (see table below).
- Use a timer: set it to 8 hours per day by default. If you have algae problems, you can temporarily reduce it to 6 hours. Additional reading tip: 6 ways to increase CO₂ .
- Choose a good lamp: go for a full-spectrum LED, with lots of red and a bit of blue. RGB lamps are also great if you want to tune the colors. Red-leaved plants (such as many Rotala and Alternanthera species) only truly show their colors with higher light intensities and stable CO₂/nutrient levels. Bottom-dwelling plants (carpets like Monte Carlo ) still require sufficient PAR at the bottom; light loses its power towards the bottom. In deep tanks or with a lot of hard scape, a little extra "power" is therefore needed to ensure that ~80–100+ µmol/m²/s remains on the substrate. Bonus: the 6 best red aquarium plants .
- Don't start too bright: many LED units are sold with the recommendation to set them to 90-100%. But that's like driving 150 km/h in a corner – the risk of veering off course (read: algae explosion) is high. It's better to start at 40-50% and increase or decrease the setting by 10% each week, depending on how your plants and algae growth respond.
- Observe and adjust: Are plants growing too slowly? Perhaps more light. Do you see algae growth? Slightly less light or shorter duration.
- Peace and quiet for fish: just like you, fish want to sleep at night. So, no 24/7 light!
Not every LED is dimmable or adjustable per color channel—and that's okay. Always consider the overall picture of your scape and your goals. Do you (temporarily) have too much light or algae? Then you can "dim without a dimmer" with floating plants like Salvinia minima or Limnobium frogbit , or by using more tall background plants that refract the light. It's all about balance and knowing which plant needs what (this is clearly stated for each plant on our site). Need advice or want to outsource the entire setup to us? Then check out our aquascape service below. Good to know: plants on wood/rock? Read which plants you can tie (hello Anubias barteri and Java fern !).
Need aquascape help?
We design, plant, and fine-tune your container. From lighting to plant selection—you say "wow," we'll take care of the rest. 💪🌿
- Personal plant & lighting plan
- Design without algae stress
- Maintenance tips you can actually keep
👉 Need some inspiration first? Also read: Plantless aquarium and increased CO₂ without expensive kit .
Wattage, Lumen and PAR for aquarium plants
| Category | Lumen per liter | PAR (µmol/m²/s) | Examples |
|---|---|---|---|
| Low light | 15–25 lm/L (~0.25 W/L) | 75–100 | Anubias , Java fern , Cryptocoryne , Mosses |
| Medium light | 25–50 lm/L (~0.5 W/L) | ±150 | Amazon sword , Hygrophila , Vallisneria |
| Highlight | 50+ lm/L (~0.8 W/L) | 200+ | Glossostigma, Monte Carlo , Red-leaved stem plants |
👉 Tip: As a beginner, it's best to start in the low or medium range. High light sounds daunting, but without CO₂ and nutrients, you'll quickly end up with a tank full of algae. Additional reading: low-light plants and solving leaf loss .
The Lighting Triangle: light, CO₂, and nutrients together form the holy trinity. If you increase the light, the CO₂ and nutrients must also increase. If you leave one corner open, algae will fill the gap. Example: carpet needs more light? Great—also add stable CO₂ and macro/micronutrients. Want to delve deeper? Read more CO₂ tips .
Common mistakes (and quick fixes)
- Leaving lights on too long: fix: use a timer and stick to 8 hours.
- Using only white light: Fix: Choose full-spectrum LEDs with red and blue.
- Too much light in low-tech tanks: fix: reduce intensity or add CO₂.
- LED at 100%: fix: start at 40–50%, build up slowly in steps of 10% per week.
Checklist
- ✔️ Timer set to 8 hours
- ✔️ Lumens or PAR tailored to your plants
- ✔️ Spectrum: lots of red, a little blue
- ✔️ Check regularly for algae
- ✔️ Fish get a day/night cycle
- ✔️ Start LED intensity at 40–50% and gradually increase
Conclusion
Lighting sounds complicated with all the terminology (PAR, lumens, spectrum), but it's actually quite simple: tailor the light to your plants, use a timer, and don't start too brightly. This way, your plants will grow healthy, your fish will stay relaxed, and you'll keep your algae under control. Need help choosing or setting up your lighting? Feel free to send us a message 📲 .
Shop directly (choose your favorite): Anubias Bonsai • Anubias barteri • Anubias nana • Java fern • Cryptocoryne wendtii • Echinodorus (Amazon sword) • Hygrophila • Vallisneria • Monte Carlo • Rotala Orange Juice • Alternanthera sessilis • Salvinia minima • Limnobium (frog bite)
Read more: Plants with low light , More CO₂ without expensive kit , The best red plants , Beginner's guide to plants , Plants on wood/stone .
