An Introduction to Aquarium Lighting


Photo by Jamieson Teo

Aquarium Lighting:

PAR vs WPG » What You Thought You Knew

In my article ‘The Three Essential Components of the Planted Aquarium’ I outlined the three most important aspects of the planted tank. Today I will go in depth, and properly explore the most important of the three: lighting. In any aquarium, lighting is an important factor, but when building an aquascape it is of the utmost importance to select the proper lighting for you plants. In doing so you ensure plant growth is optimal and algae growth is inhibited.

An over abundance of lighting normally results in unfavorable algae growth. This is usually the result of an uniformed aquarist. It is a common beginner mistake to use the age old method of WPG or Watts per Gallon. In years passed this was sufficient for aquariums run on fluorescent or halogen bulbs. However, in recent years lighting technology has changed with the advent and ubiquity of LEDs and CFLs. These lights no longer operate through wattage, rather they are given an ‘equivalency rating’ which all but renders their wattage useless.

In an attempt to adapt to the change in technology, fellow aquarists, engineers and biologists have slowly begun to move away from the WPG rule and have begun to utilize the new more accurate PAR rating. Plant biologists define light in the 400nm to 700nm spectral region as “photosynthetically available radiation,” or PAR. PAR is measured in micro-mols per second (μmol/s), and is not similar to Lux, Lumens, or WPG. PAR is a measure of photosynthetic viability and as such it is exponentially more valuable to us growing plants.

Furthermore, PAR is not just a static reading. Every light source has a different propensity to penetrate water. Simply put, PAR decreases as we move our light source further away from the aquarium substrate. To harness the power of PAR we must properly measure it.

par ranges

As PAR increases, the light in you tank increases

How to Measure PAR

PAR is a relatively new unit of measurement for the aquarist, as such, the methods of measuring PAR are unreasonably expensive. To compound the problem, the most accurate of PAR meters can rarely be found outside of a scientific lab.

Thankfully, many scientists, manufacturers and hobbyists before us have solved the problem.


How Much Lighting is Enough?

aquariuam lighting planted tank
Choosing the right aquarium light for your planted aquarium should be one of the last things you check off when you are building your aquascape. First and foremost it is essential to decide the types of plants and the needs of those plants. More often than not the description of a plant will have the lighting needs (low, medium, high) published on the product page before you buy it. Use that information to select plants that you will be capable of, or choose to maintain. When you have selected the plants it is time to meet their other needs; CO2, Fertilizer, suitable substrate etc. then the lighting should fall right into place.

  • Low light – 15-30 PAR – CO2 is not needed
  • Medium light – 35-55 PAR – CO2 recommended to avoid algae
  • High light – 55+PAR – pressurized CO2 essential to avoid algae


The Three Most Common Aquascape Lighting Solutions

T-5 HO (High Output)

Very similar to the original tube style fluorescent lights, high output lighting is known for its ability to create much more intense light. Beginners usually gravitate towards HO lighting solutions because they are inexpensive, easy to find, and the idea of not having to worry about “getting enough light” is enticing. In fact, this becomes a major problem. More often than not, HO bulbs are too much light. Beginners overestimate the power of these bulbs which results in an overabundance of algae growth. If you choose to use HO bulbs be sure to do diligent research regarding the products PAR, and if you are experiencing algae with your HO bulbs consider raising your lighting a few inches (remember this reduces PAR intensity).


Also a type of fluorescent lighting solution, CFLs have quickly become a favorite of aquarists because they fit into regular bulb sockets and can be found in nearly any hardware store. CFLs range in color temperature (Kelvin) widely, and though color temperature is not a factor in plant growth it is an important aesthetic decision to make. The most enjoyable color temperature is at 6500K and imparts just a slight bluish hue to your water. In addition, wattage should not be trusted and due to the equivalency rating, a proper PAR rating for your bulbs should be researched.


LEDs are becoming the staple of the aquascaping hobbyists tank. With the introduction of the Finnex Fugeray Planted+ and other similar lighting solutions, manufacturers have all but removed the research and guess work from choosing a lighting system. They offer a variety of features and PAR ratings to meet any of your plants needs. In fact, Finnex just recently announced a new line of aquarium lights with built in timers and a function that simulates Sunrise and Sunset.



  • Forget WPG, PAR is king
  • PAR is a measure of photosynthetic light intensity
  • PAR decreases the further you move your light source away
  • Choose lighting that fits your plants needs
  • Manufacturers provide us with simple solutions for beginners



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Hi I'm Ryan, the owner of Aquathusiast. I've been keeping fish and aquatic plants for several years now. Along the way I've learned a lot. My goal is to take that knowledge and experience and help you, my readers, create the best aquariums and aquascapes possible. Drop us a line at or join us in the forums for a free aquarium consultation.
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