Aquarium Lighting Basics

Learn why lighting is so important for your freshwater aquarium.
Aquarium lighting plays a big role, much bigger than simply illuminating an underwater world for your viewing pleasure. Lighting also provides energy and oxygen to ensure the overall well-being of your pets, as well as growth for photosynthetic plants and organisms. Light is essential for the healthy growth of fish, plants, corals and bacteria…all life in your aquarium’s environment.


  • Wattage – the amount of energy used
  • Kelvin – the color of the lighting (low is a warm color, high is a cool color)
  • Lumens – its brightness (as perceived by the human eye for general illumination)
  • PAR (Photosynthetically Active Radiation) – the light that is useful to grow plants and beneficial algae
  • Fluorescent – It’s the most common type of lighting available and traditionally the most inexpensive. It’s well suited for freshwater fish and planted aquariums and comes in a variety of sizes to fit any aquarium hood or light fixture. Fluorescent bulbs are circular tubes and tend to be inefficient due to a portion of emitted light being reflected upward, away from the aquarium.

  • T-5 HO (High Output) Fluorescent – A more advanced type of fluorescent, T-5 HO bulbs are almost twice as bright as standard bulbs. This type of lighting is ideal in larger tank environments that require brighter, deeper penetration and a mix of bulb types. T-5 HO bulbs generate a significant amount of heat, so be sure to monitor the temperature inside your aquarium regularly and turn off the T-5 lights when necessary.

  • LED (Light Emitting Diode) – Relatively new to the aquatics scene, LED lighting is fast becoming the favorite for aquariums due to their slim design, shimmer effects and colors, cool operating temperatures, and low cost to operate. A wide selection of sizes and types are available for any aquatic environment. LEDs also generate a consistent color of light through their lifetime. This is an advantage over fluorescent lights that experience a shift in color spectrum (white to yellow) over 3-6 months.

  • Planted Tank: 6500 to 7500 Kelvin 15-30 PAR for low light plants, 30-80 PAR medium, 80+ PAR high light plants
  • Fish Only: 5500 to 6500 Kelvin for general viewing. Unlike plants, fish do not have a biological need for light, so they require less. Natural sunlight at noon has a rating of 5500 Kelvin.
  • Marine Reef Tank: 300-500+ PAR in general for soft and hard corals
  • GloFish®: A new entry to aquatics; fluoresce while under a blue spectrum light or black light

How long should I keep my aquarium lights on?

To provide animals and plants the lighting they need, 10 to 12 hours a day is sufficient. Installing a timer or purchasing a unit with integrated timing can make lighting easier––just set it and forget it. Keep in mind algae loves light as well. So if you notice algae growth starting, cut back on the duration. Another option is to leave the lights off while at work and have them on when at home.

Do I need a glass canopy?

If your lighting is exposed, meaning it doesn’t have a protective cover over the bulb or LED, a glass canopy is recommended to extend the life of the unit by preventing moisture from affecting it.

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