WHAT IS IT AND WHY DO PLANTS NEED IT?
Lighting is a vital component in growing healthy plant life. Plants utilize the radiation from our lights to stimulate photosynthesis. We need to be conscious of the light we choose for the specific plants we are growing because plants need enough light to live, but excess light can cause algae blooms and harm plants. And different plants have different light requirements. Once we have light intensities where they need to be for our design, we can consider the temperature, or Kelvin, of the lights. Doing so can make certain colors in our plants pop.
I like to teach that your light should be kept on 8 hours a day, no more, no less. It is best to utilize a timer to automatically control their tank’s timing as we don't want too much light. Generally, we try to keep our tanks away from any natural sunlight from hitting our tanks in order to have more control of the light. If algae occurs after your tank has been set up for 6-8 weeks, you'll want to dim your light back a bit, or consider raising the light higher up by another 1-2” and see if algae subside.
Time your CO2 so that it is on 1 hour before your lights are on. This way Co2 saturation levels are high as soon as your light turns on kick starting photosynthesis.
MEASURING LIGHT– What is PAR?
Today, aquarium lights are typically measured in PAR, which stands for Photosynthetic Active Radiation. This is a way to measure the amount of light that will stimulate photosynthesis for a plant. Photosynthetic Photon Flux meters (PPF, PPFD or PAR meters) can be purchased to read a light’s intensity. What are we measuring? Well, when light travels away from the source that is emitting it, the light loses intensity. Also, when light has to travel through something, like a screen over our aquarium, it also cuts the intensity.
This falloff not only happens straight down but from side to side as well. Prior to LED lights, most hobbyists measured their light intensity by the “watts per gallon” method. This is a measurement of how much energy a light uses and doesn't tell us much about its ability to stimulate photosynthesis. Similarly, we see manufacturers talking about a light's lumens, but this is just a measurement of how our eye perceives the intensity of the light and has nothing to do with PAR. Lastly, we see companies quoting a lights Kelvin, like 6500k. This is just referring to the light's color temperature, or just how orange or blue a light is... again, nothing to do with PAR. Kelvin does play into the light spectrum which we'll talk about is the next section.
So what do I recommend? I recommend starting off with a dimmable LED light with a PAR value of around 60-80 PAR. I would also get a light with as many different colored LEDs as possible to make sure our plants are getting as much of the light spectrum as possible. More information on that down below.
When selecting a light, again, we need to focus on its PAR to give us an idea of how much it will stimulate plant growth. Most major light manufacturers will measure their light’s PAR for us. I would highly suggest not buying a light without knowing its PAR values as we have no idea how well it will grow plants. It could be too little light, and our plants won't grow at all. Or it could be too much light and cause our tank to be overgrown with algae. But as a stake in the ground, these values are what is currently accepted by the community as low, medium and high lighting.
PAR Rating: 10-40 is considered low light.
Remember that when choosing a light, we want to pick a dimmable light between 60-80 PAR range to make sure we don't have too much, or too little light. More cost-effective lights generally have a lower PAR rating and are not adjustable. More expensive lights generally have a higher PAR rating and we can adjust the intensity. Some fancy pants lights can even be controlled by our smartphone app!
If you already have a light in that PAR range, but cannot adjust your light’s intensity, you can always physically raise and lower the light off your tank to effectively adjust its intensity. Generally, hobbyists will raise and lower a light fixture by 1-2 inches when testing. If you are raising it due to excess light, give your tank a couple of weeks to adjust to the new PAR values its receiving. There are other types of lights we can choose from, like fluorescent or metal halides, but I don't suggest them as they are less cost-effective as they use more energy, and they can be noisier light fixtures... and the last thing you want for your relaxing aquascape is noisy lights.
Another thing we need to keep in mind is the light's spectrum. In a study that the University of Michigan conducted, they found that red LEDs grew plants the best. Green was second, and blue was dead last. We now know how that warmer lights, or lights with more red LEDs will grow plants better than cooler ones. If you have a programmable LED light and would like to learn how to dial it in to maximize growth, click on our blog post named "Dialing in your programmable LED aquarium light" to learn more!
WHAT DO I RECOMMEND?
To recap, I recommend a medium PAR light (60-80 PAR) that is dimmable. Here is why:
You'll have less algae due to an excess of light
Medium PAR lights will also make for less trimming and maintenance on fast-growing plants
Having it dimmable will allow you to dial the intensity up or down to customize it to your tanks needs
LED lights are generally more compact which mean more focus is on the aquascape and not the giant spaceship-like device hovering above your aquarium
LED lights with lots of red LEDs
Two pitfalls to avoid:
1) Make sure you buy an appropriate light for the plants you are keeping. Don’t get a high PAR light for a bunch of low-light plants if you can not dim the light. And vise versa, don't get a low PAR light and try and grow a bunch of high light plants.
2) I would avoid pendant lights (like a Kessil light) if you have a wider tank. Square form factors tanks are ok. Pendant lights have a very small and circular light profile/spread versus something like a TwinStar light which is a big grid system of LED. This can sometimes be combated with a side lense at the bottom of the light, spreading the light wider, but then PAR is reduced as more light is being scattered versus concentrated. A light with a larger grid-like layout will provide an even light intensity throughout the tank making it easier for your plants to get the light they need. Again, pendant lights are not a bad option, I would just recommend using them on smaller or square profile tanks or when the scape design is mostly hardscape with a centralized cluster of plants that fit within the narrow spread nicely. We also see aquascape light, George Farmer, using two pendant lights to equally distribute across a wider tank.
I have some recommendations for you all below in the related products section.
Hall, David O.; Rao, Krishna (1999-06-24). Photosynthesis. Cambridge University Press. pp. 8–9.