Aquarium light questions answered
Updated June 2026Independently researchedNo paid placement.
Choosing the right aquarium light comes down to what you’re growing, plants or corals, and the size of your tank. Full-spectrum LEDs are the most versatile and energy-efficient option for most hobbyists. Start with a moderate intensity and adjust based on how your plants or livestock respond.
What kind of light do I need for a planted aquarium?
For a planted tank, you want a light that provides enough intensity (measured in PAR) for photosynthesis and a spectrum that includes red and blue wavelengths. Most standard aquarium LED strips marketed for plants will work for low-light species like anubias and java fern. If you’re trying to grow a carpet of dwarf baby tears or other demanding plants, you’ll need a higher-output fixture, often one with multiple LED channels or a programmable dimmer. Don’t just look at wattage; pay attention to the fixture’s spread and depth rating. A light that works on a 20-inch tall tank may not penetrate a 24-inch deep one. Many manufacturers publish PAR maps that show intensity at different depths, those are far more helpful than a simple lumen count.
Do I need a special light for a saltwater tank?
Yes, especially if you keep corals. Soft corals and fish-only saltwater tanks can get by with a basic full-spectrum LED, but stony corals (LPS and SPS) require much higher PAR and a spectrum that peaks in the actinic blue range. That blue light drives photosynthesis in the symbiotic algae living inside coral tissues. Look for fixtures labeled specifically for reef aquariums. They usually have separate channels for cool white, royal blue, and sometimes violet or red LEDs, giving you control over color and intensity. Many of these lights also come with built-in timers and ramping features to simulate sunrise and sunset, which reduces stress on your livestock.
How long should I leave my aquarium light on?
A photoperiod of 8 to 10 hours is a solid starting point for most tanks. If you’re battling algae, try cutting it back to 6 hours and see if that helps. For planted tanks, aim for a consistent schedule, plants and algae alike dislike irregular lighting. It’s also smart to use a timer or a light with a built-in controller. A Siesta break (a few hours off in the middle of the day) used to be popular, but stable 8-hour stretches work just as well for most setups. Observe your tank: if you see sudden algae blooms or your plants look pale, adjust the duration and intensity rather than the spectrum.
What is PAR and why does it matter?
PAR stands for Photosynthetically Active Radiation, it measures the amount of light in the 400 to 700 nanometer range that plants and corals can actually use for photosynthesis. A light may look bright to your eyes but deliver low PAR, especially at the bottom of the tank. For most low-light plants, you want a PAR of roughly 20 to 50 µmol/m²/s at the substrate. Medium-light plants need about 50 to 100, and high-demand plants or SPS corals often require 150 or more. When you read reviews or manufacturer specs, look for PAR data at specific depths. Without that, you’re guessing, and guessing often leads to algae or stunted growth.
Can I use a regular desk lamp or household bulb instead of an aquarium light?
It’s not ideal. Standard incandescent or compact fluorescent bulbs lack the spectrum and intensity that aquatic plants need, and they often produce too much heat, which can raise your tank temperature. LEDs meant for general use also may not be fully sealed against humidity, creating a shock hazard. If you’re in a pinch for a very small tank with only low-light plants, you could try a clip-on lamp with an LED plant bulb, but you’re better off with a purpose-made aquarium light. The extra cost is small compared to the risk of a tank full of unhappy plants or a short circuit.
Frequently asked questions
Should I get a light with a built-in timer?
A timer is one of the most helpful features because consistent photoperiods reduce algae and keep plants on a steady growth cycle. Many mid-range and higher LEDs include programmable timers; if yours doesn’t, an inexpensive outlet timer works just as well.
What’s the difference between low, medium, and high light?
These terms refer to the PAR intensity at the substrate. Low light (20–50 PAR) suits shade-loving plants like java moss and anubias. Medium light (50–100 PAR) supports stem plants and most crypts. High light (above 100 PAR) is needed for demanding carpeting plants and many corals, but it often requires CO2 injection to avoid algae.
Do I need to replace the bulbs in an LED aquarium light?
Not like you do with fluorescent tubes. LEDs don’t burn out suddenly; they gradually lose brightness over many years. However, the spectrum can shift over time, so after 3 to 5 years you may notice your plants growing less vigorously, and replacing the fixture may be worthwhile.
Will an aquarium light cause algae?
Any light can promote algae if the intensity is too high or the photoperiod too long, especially in a tank that doesn’t have enough plants to compete for nutrients. To minimize algae, start with a shorter photoperiod (6–7 hours) and avoid placing the light too close to the water surface.
Can I use the light that came with my aquarium kit?
Kit lights are usually very weak, fine for basic fish viewing but rarely enough for healthy plant growth. They often have a narrow spectrum skewed toward cool white. If you want to grow anything beyond the hardiest plants, budget for an upgrade. A decent entry-level LED fixture makes a much bigger difference than you’d expect.