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Simulating the Sun Path in Planted Aquariums

Updated: Nov 14, 2021

I recently installed a Twinstar LED light on my 38 gallon planted aquarium. It replaced a Finnex Ray 2. If you know anything about the Twinstar line, they are considered top three in the list of planted tank lights. They have a full rich color and bright intensity. So bright is their intensity in fact, that I installed an inline dimmer. The Finnex I had did not allow for a dimmer so it was at full intensity for the entire time it was on, which could only be about seven hours. Any more than that and algae growth would become an issue. That gave me barely any time to enjoy the tank and did nothing to simulate any kind of natural aesthetic.

With the new Twinstar and dimmer I am able to ramp up from 0% intensity at 11am to 100% by 2pm and then from 100% at 7pm to 0% at 11pm. This allows for the light to be on for 12 hours, giving me much more time to enjoy it, plus it simulates a sun path, or the relative intensity of the sun's light as it travels across the sky during a day. So as a biologist, I immediately wondered, besides my enjoyment, how does my new lighting schedule effect my fish and plants, if at all? I started by diving into a little research.

First, some basic well known plant facts. Plants grow toward the light, they grow taller vs. wider if the light is too dim. Day length can also trigger flowering in flowering plants. So how does this affect plant growth if the light is "too dim" for a portion of the day?

In 2019, a hopeful graduate of Rhein-Waal University in Kleve, Germany submitted a thesis on the effects of light intensity and duration on lettuce growth. He had three groups to compare. The first group received 40 minutes of reduced light at the beginning and end of a 16 hour period. The second group received 20 minutes of reduced light on the same schedule. The third group was the control and received full intensity for the full 16 hour period. After measuring leaf growth and biomass at 12 and 24 days, he concluded that the control group grew the most, followed by the second group with the first group having grown the least.

So, my special schedule isn't simulating nature in such a way that my plants think they are back home in the marshes of Thailand or the Amazon River and thus grow more fervently. Perhaps the way they grow, the color they produce or the pattern in which they leaf is affected? Based on what I could find in the journals I had access to, it looks like I'll have to do my own research.

So what about my fish? Surely simulating the sun path must benefit my fish as they react more quickly to environmental changes than plants do. There is some anecdotal evidence that ramping the light up in intensity prevents fish from jumping as the sudden 0 to 100 can startle some species. It must be less stressful for them at the very least. According to Saether in a paper published in the Journal of Fish Biology, simulating natural day lengths has no affect on food consumption in Arctic char... at least not seasonally. While their results are a little bit of a stretch from my home aquarium, I'm still convinced there must be some effect on my little tetras as they greet the morning sunrise I've so carefully crafted for them.

Even if my lighting schedule is just for me, I'm going to continue to watch carefully, take diligent notes and compare to previous conditions. Hopefully soon, I'll have an update as to whether simulating the sun path in a planted tank has any biological effect on the flora and fauna inside.

For more information on how I set my schedule, the products I used, or my hypothesis on it's effects, scroll down to contact Brian at Boodleshire Aquatics.

  • Albot, D. "Impact of a shift in the light spectrum on lettuce growth. Simulation of sunrise/sunset using adjustable monochromatic LED lights. Rhein-Waal University. 2019.

  • Saether, B.S., et. al. "Seasonal changes in food consumption and growth of Arctic charr exposed to either simulated natural or a 12:12 LD photoperiod at constant water temperature" Journal of Fish Biology. 48:6. 1996.


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