What is the best light for aquarium plants?

Aquarium plants need lighting with the right spectrum if they are to be healthy and grow properly. This may be slightly different to the stock lights supplied in your aquarium package so many planted tank owners and aquascapers swap their lights out for those with dedicated plant spectrums.

The colour of light is measured in something called Kelvin, and most plant lights have a Kelvin rating between 6500 and 9000, with 6500K having a yellower hue and 9000K having a whiter hue. Plants actually enjoy the red spectrum of light, right down to about 3000K, but this doesn’t make the aquarium look very aesthetically pleasing so most plant growers use either a single lamp or several lamps with RGB (red, green, blue) in their spectrum to both enhance plant growth and bring out the rich reds of fish and plants to the human eye. 

Plant growers tend to use either fluorescent light tubes or LED for plant growth. Fluorescent has been used for decades and if you provide plant spectrum tubes and enough of them for the depth of tank, plant growth should be enhanced. Reflectors can be used for increased light output down into the tank and T5 tubes are the brightest available. If using multiple T5 a combination of plant, natural daylight, cool white and colour enhancing bulbs can be used to achieve the best overall look and colour. 

LED lamps are also available in tube form to mimic and even fit into T5 lamp holders, again available in several spectrums to encourage plant growth, give a clean, white look, or enhance colours. Opt for an open-topped tank and high powered LEDs can be mounted to the tank rim to provide very bright light for plants that require it.

Many use fan cooling (so don’t drop them in the water,) but have the advantage of app control and colour, brightness and duration that is programmed by the user. This enables a perfect balance of spectrum and output and can even fade in and out to simulate dawn and dusk. 

Lush plant growth is made possible by light, fertilisation and CO2

Fertilise your plants for better growth

Healthy aquatic plant growth is not all about light, however, as plants also need plant food to fuel growth. If you increase the lighting in your planted tank but not increase the amount of plant food your plants may become leggy, weak and succumb to opportunistic algae, which also enjoys bright light. Not all plants require bright light either, with Anubias from West Africa naturally inhabitting shaded forests. 

And if you want the ultimate in plant growth complete the triangle of light and nutrients with Carbon Dioxide, which plants use to build their structures. Use a combination of the right lighting, fertiliser and CO2 for the ultimate in plant growth in your aquarium. 

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Jeremy Gay is an author, lifelong fishkeeper, and aquatic specialist. He's a former editor of Practical Fishkeeping Magazine, UK editor at Reefbuilders, a former aquatic store manager, and has collected fish in Sri Lanka and the Amazon. He's been on tv and radio, contributed to Koi Carp and Gardeners World magazines, been a product tester, a judge, and a product developer. Jeremy is here to guide and advise you on all things tropical, pond and marine, from set-up to stocking, health, feeding to breeding, as well as solving many common fishkeeping problems along the way.

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