What Size LED Lights Do I Need for My Aquarium?

LED lighting is known to produce an ethereal glow when used in standard aquariums.
LED lighting is known to produce an ethereal glow when used in standard aquariums. (Image: Ablestock.com/AbleStock.com/Getty Images)

Light-emitting diode (LED) lights are popular in aquariums, because they don’t have the overheating issues associated with fluorescent lights. Switching to an LED aquarium light will require a specific size LED fixture that is dependent on the type and size of aquarium you own. Typically, sizing will depend on tank size and Kelvin rating. Photosynthetically usable radiation (PUR) and photosynthetically active radiation (PAR) also have a role in LED lighting.

Tank Size

LED lamps can be selected based on the size of your tank. For a tank that’s 18 to 22 inches, a 16 ½-inch LED lamp should suffice. For a wider tank, mount 2 rows of LED lamps or increase to a larger size. For example, a 24- to 30-inch aquarium that is 12 inches wide, would be lit best by a single 21 ½-inch LED lamp. For a tank that’s 18 inches wide, you’ll want to use two LED lamps to heat the front and back of the aquarium adequately.

Kelvin Rating

Your aquarium may call for a lamp that’s carries a specific Kelvin rating. This information would be located in the aquarium’s instruction booklet. The Kelvin rating defines the color temperature of a light bulb. LED lamps with higher Kelvin ratings produce cooler colors, such as blue and green. Lower Kelvin ratings produce warmer colors, such as yellow and red. An LED lamp should specify its Kelvin rating on its packaging, but if it doesn’t, inquire with the salesperson or contact the manufacturer.


PAR describes any light in the specific frequency of 400 to 700 nanometers. PAR is used when there is a specific need for this frequency, because the aquarium contains living plants or symbiotic zooanthellic algae. Look for LED lights that specify a PAR frequency if you have living plants in your tank.


PUR defines the useful light energy in PAR. PUR lighting is used in aquariums that contain photosynthetic plants, as well as clams and corals. PUR is affected most by the depth of your tank, so consider this when looking for a viable LED lighting option. Only high-end LEDs are measured in PUR. Lower-end LEDs do not have the advanced circuitry and drivers needed to measure usable radiation.

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