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 (PAR) where they need to be for our design, we can consider the spectrum (PUR). Doing so ensures your plants will have all the energy they need to be happy and healthy.
VARIABLES IN LIGHTING
Lighting has 3 main variables:
Time - How long we keep the light on for
PAR (Intensity) - How much energy the light produces for plant growth
PUR (Spectrum) - Of that energy the light produces, how much can the plants actually use
Right out of the gate we suggest you put your light on a timer, or program it to only be on for 8 hours a day. If we need to adjust the light we will do so adjusting the intensity (PAR) and spectrum (PUR) of your light. Running your light for longer than 8 hours a day can just lead to algae. Hobbyists also focus on the wrong values, like lumens and watts . These are older ways we used to try and estimate PAR and PUR, but we no longer use these values anymore.
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.
WHAT IS PAR AND PUR?
PAR, stands for Photosynthetic Active Radiation. This measures of the amount of radiation a light outputs that stimulates photosynthesis. This measurement, combined with PUR, allows us to see how well a light is going to grow plants.
PUR stands for photosynthetic usable radiation. Of the PAR measurement, how much of that is usable by plants. We want to dial in our PUR (spectrum) to ensure we are blasting our plants with light they can use.
THE DIFFERENCE BETWEEN PAR AND PUR
Just because a light has a high PAR (intensity), doesn't mean its PUR (spectrum) is usable by plants. An example of high PAR, but bad PUR would be if we put a reef light on a planted tank. The PAR of the reef light might be amazing, but because its mostly blue and UV light in spectrum, our plants are not going to be able to use it. So the light has great PAR, but low PUR.
So what do plants need. Accroding to two studies produced by the Michigin State and Utah State universities, plants love tons of red in their spectrums. Red helps increase plant mass, and larger plant mass means more area for photosynthesis. They also like a medium amount of green, and little to no blue in their spectrums. The universities found that if a spectrum has more than 10-15% blue in them, this decreases plant mass, thus reducing surface area for photosynthesis. So in our spectrums we want a TON of red, around 50% green, and 10-15% blue. We cover all of this AND reference the studies by the two universities in the article Dialing In Your Aquariums Light's Spectrum. Since Fluval had to go off and be "special" with their lights leds, we ended up writing an artitcle specific to them named "What Settings Should I Use For a Fluval 3.0 Aquarium Light"
So how does this play out with cheap, versus expensive lights. When one buys a cheap light, like one from Nicrew or Hygger, their PAR are good to some extent, but the PUR is not sutibule for plant growth. And what good is a high PAR if the plants can't use the spectrum its outputting. The images below compare the light spectrum from a Hygger 24/7 light versus the Chihiros WRGB II. Look at the spectrums of the Hygger, it has an output of 140PAR, but the spectrum is comprised mostly of blue light with little to no red in the spectrum . The Nicrew full spectrum planted tank light has close to the spectrum at 110PAR. Where if we set the Chihiros to follow what Michigan and Utah state found, we would almost get the inverse of what Hygger and Nicrew gives us. TONS of warmth, and nice amount of green, and very little blue. So even thought these lights put out a good amount PAR, the plants can not use most of the lights spectrum for plant growth.
MEASURING AND CONTROLING PAR
The hard part with PAR is the only way to measure it as a hobbyists is with a PAR meter. However, these can be really expensive. So how do we measure PAR levels in our aquarium? Here are the two ways we can guesstimate PAR without a PAR meter:
1) We recommend buying a dimmable LED light from a manufacture that provides their PAR data. Most creditable manufactures like Finnex, Twinstar and Chihiros share their PAR data. Now this is just a guestimate, but if the light outputs 120PAR at 12" while at full blast, dimming it down to 50% would put us at around 60PAR at 12". Having provided PAR values from the manufacture gives us a better guesstimate on the PAR of our light affording us more control.
If a light manufacture does NOT share their data, it makes us suspicious that they don't want you to know what it is. Furthermore, cheaper lights from companies like Nicrew and Hygger will entice customers with higher PAR levels but their PUR is the opposite of what plants need. More on PUR later.
2) If you can not find your PAR information online, the best thing to do would be to measure it with a PAR meter yourself. The issue with that PAR meters are hundreds of dollars. However, there is a new app named Photone made assessable on the Apple Store, and Android Play Store. Photone turns your smartphone into a PAR meter! We wrote a little article on it named "Use Your Smart Phone As A PAR Meter...". We also used the Photone app in our recent review of the ONF Flat Nano+ you can watch below.
WHAT DO I RECOMMEND?
Start off with a good light. Stick with Finnex if you're on a budget. If you want a long term light, we'd suggest a TwinStar model S or Chihiris WRGB II. Links to all of these at the bottom of the page.
If you are NOT Co2 injecting, look for a light that will give you around 80-85PAR, and make sure to not go higher than that. We really like the Finnex CRV light, which is down at the bottom of the page as well. This puts you around 80PAR at full blast and has dedicated red LEDS to help boost the warmth in the light as talked about above. The only downside with this light is we have to chose between 6 and 9 hours, so you'll either need to pick one of the two, or keep it on all the time and set it up on a timer.
If you ARE CO2 injecting, I would suggest running you light around 120 PAR at the substrate. We really love Twinstar and Chihiros lights as they have an AMAZING PAR and PUR. The only downside with the Twinstar is that it isn't bluetooth controller, so you can not dial in the spectrum, or set up a timer for it internally. The intensity is controlled with an inline controller, and you have to set it up on a timer. Its not the end of the world as the Twinstary comes with an great spectrum out of the box, but the control is nice. And the Chihiros WRGB II is hands down our favorite light at the moment. If you didn't need all the PAR is has to offer, you could get their slim model for shallower tanks, or if you're not running CO2, you can dial it back.
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.
Hall, David O.; Rao, Krishna (1999-06-24). Photosynthesis. Cambridge University Press. pp. 8–9.