The proper Light for Aquarium Plants

This topic can’t be described in general. There are many suggestions to run an aquarium in a hardly lit room and to protect it from direct sun irradiance if possible. However, aquarium plants are gathered from nature und obviously need sun light. The difference is, that these plants almost ever live on places where water can stream around them, the water’s bacteria are stable established like in an aquarium which is well conditioned. In nature, plants are perfectly adopted to their environment, sun irradiance, water hardness, pH-Value, nutritionally of the water, water’s CO2 content, etc. In a plant aquarium someone can only try to imitate the light an all other influences. A matter of fact that there is no streaming “fresh” water available, someone may reckon with a growing population of algae when the tank is exposed to direct sun irradiance, even though you manage several partial water changes a week. A remedy is an aquarium light whose light comes as close as possible to light of sun, but in a damped form. Too strong light leads to algae, especially in new aquariums, i.e. where the bacteria still didn’t have the chance to develop a stable equilibrium which comes as close as possible to the one in nature. New installed tanks, where moreover the soil still has too much nutrients a daily partial water change is recommended from the soil manufacturer. Considering the facts of above, the irradiance of direct sunlight would be practically said “poison” for such an aquarium and can even lead to a water’s green color change. It is not topic of this article, but I would like to mention, that algae like higher temperatures, so a tank temperature smaller than 25°C would be optimal.

Spectral Distribution of the Proper Light

As we all know, light can be synthesized with the three basic colors red, green and blue. The mixture of these three colors yields white. Plants always appear in green, but why? The reason for that is, as we all know, the so-called chlorophyll, which takes care of the photosynthesis, converting CO2 to O2 (oxygen). For that it needs blue and red light. The green part of the light is reflected by the plant. In case someone would expose a plant with merely blue and red light, the plant would appear in gray. The verdurous and fresh green is only seen because of the green part of the light source, which is responsible for that. More overly, human eyes are most sensitive for the color green, a matter of fact that that green exactly lies in the middle of the spectral distribution of sun light.

The conclusion is: In order that plants in a tank appear as accurate as possible a spectral density is recommended as close as possible to the one of sun light. If you buy a luminant, e.g. a fluorescent tube or a LED, mostly they come with important figures. The two most important in this topic are the color temperature and the so-called Ra-value. The surface of the sun is blazing hot and therefore emits visible light with a color temperature equally to the temperature of the sun surface (ca. 5500°C, i.e. ca. 5800K). At that temperature the light of the sun appears “glowing” white. White light with exactly the three basic colors red, green and blue. Without going further into detail, the sun shows a spectral distribution as depicted above. The Ra-value of a light source is an indicator how accurate a light source can imitate the sun and is expressed in percent. The higher the better.

Picture A shows a plant aquarium lit with a lightsource at high Ra-value (daylight). Color reproduction of the plants is nice. Picture B shows the same tank lit with a light source at lower Ra-value. Plants appear a bit more gray (Picture Tropica)

That’s the light amount your plant aquarium needs

A recommendation for that can be found here:
Light Calculator (in German)
Tropica offers InVitro plants in three different degrees of difficulty:

  • easy
  • medium
  • advanced

which correspond to the light needs “niedrig”, “mittel” and “hoch” , respectively.

Calculation example

ADA Cube Garden 90P with the dimensions 90x45x45 (cm). 182 Liter volume brutto. At low light needs (“easy”) of the plants and no CO2 adding, the result is 15 Lumen/Liter, i.e. a light with 2.733 Lumen is needed. The same tank with high light needs and CO2 addition needs 50 Lumen/Liter, i.e. 9112 Lumen.

Therefore, a bought, universal applicable LED light should be able cover this bandwith in light strength.
After a long search in forums and LED lights on market, I did not find one fullfilling these demands!

Investigating furhter I came to the following conclusions:

  • As good as all lights do not give information of the used LEDs
  • All lights have a fixed brightness and only can be dimmed with an external 230 V dimmer.
  • There is no LED light on market which accomplishes 9000 Lumen (for a ADA 90P)
  • Almost all LED lights have a very high current consumption. Only cheap LEDs are beeing used, e.g. 80 Lumen/Watt. At 9000 Lumen this would lead to a current consumption of 125 Watt!! at the power plug 10-12 hours per day
  • All dimmable aquarium LED lights are not flicker free!
  • All reasonable LED lights are very expensive. Especially when you want to reach 9000 Lumen you even have to buy two
  • No LED light provides a wireless controller to adjust the brighness
  • All LED lights come with a big heatsink because of their low efficiency.
  • As good as all lights have a color temperature of 6500K-7000K

The last is a consqeuence of, that most of the aquatics users prefere a slightly blue colored light. This is because the OptiWhite glass appears with no hint of green and plants as fishes look more interresting.

Considering the above investigation  I decided to build my own aquarium light! My results are: Branded LEDs with A++ efficiency, Ra-value of >80 oder >90, with garanteed 175 Lumen/Watt. Absolute top, state of the art. While other lights are not flicker free, mine is by design absolute flicker free (true current limitation instead of PWM) and the brightness can be controlled wirelessly via a 2.4GHz transmitter. Even ADA does not offer lights like this and only offers them till 60cm in length. My light is easily scaleable und can be utilized for tanks in every length from 60-120cm. Due to its efficiency and its used LEDs it does not get warm and needs no heatsink. The brightness is awesome and features 7500 lm for a 90cm tank and that at a current consumption at the power plug of only 48 Watts.