How Long Should I Leave My Aquarium Light On?

Proper lighting ensures the happy healthy life of aquarium plants and fish.
i Jerry Yulsman/Photodisc/Getty Images

Proper aquarium lighting is essential to fish and aquatic plants; it brings an aquarium to life. Beautiful aquariums can be stunning home attractions, bringing families together. Lighting plays a key role in creating striking aquatic scenes, but it is important to realize that different aquariums have different lighting needs.

Heat-Producing Lights

Incandescent, VHO–fluorescent and metal halide lights produce lots of heat. Of the heat-producing lights, incandescent are the most common. They are inexpensive and versatile, but it is not advisable to leave them on too long. The smaller the aquarium, the more susceptible they are to sharp temperature rises. Leaving the lights on for extended periods or even overnight could prove deadly to an aquarium’s inhabitants. Frequently monitor the water temperature to get an idea how long you can safely keep the lights on (usually a few hours for 10-gallon aquariums). The house temperature, location in house (i.e. near a window), size of the aquarium and kinds of fish and plants are all factors in your decision. VHO (very high output), compact and metal halide lights are normally used by more experienced hobbyists, who often use ventilators in addition to their lighting systems to maintain consistent temperatures.

Cooler Lights

Normal output fluorescent lights are common, inexpensive and produce less heat. They can be left on safely for long periods and are a great choice of lighting for hobbyists. Many tropical fish and plants can thrive in fluorescent lighting.

Tropical Fish and Plants

Native tropical fish and plants live within 23 degrees of the equator and experience about 12 hours of light and darkness. To recreate tropical conditions, leave the aquarium light on for 12 hours a day. Some tropical fish, such as the elephant nose fish, prefer dim lighting, and so if they’re included, provide them with plenty of hiding spaces.

Tropical plants add beauty, color and often become food supplements for fish. They thrive in proper lighting, producing oxygen and remove harmful waste products. Common tropical “beginner” plants include the banana, Amazon, Java, and fern plants.

Coldwater Fish and Plants

Goldfish, minnows, ricefish and dannios (zebra fish) live in temperate zones where daylight hours fluctuate with the season. To create a more natural environment, match the seasonal daylight hours with the aquarium lighting. There are many varieties of cold-water plants that can thrive in the home aquarium (i.e., Anubias species and tiger lotus).


Placing a tank too close to a window receiving direct sunlight can cause excessive algal growth. The addition of artificial lighting can exacerbate the condition. Some algae are beneficial; especially for algae-eating fish, but excessive growth obscures the view. If a tank must be kept near the window, balance daylight hours with lighting, distance from windows and the types of fish to control algae. Sometimes getting it right is a matter of trial and error. An algae scrubber can always restore the view if growth gets out of hand.

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