Are Aquarium Lights Necessary?
Aquarium lights are critical for live plant growth and for the general look of your fish tank. Plants use light and CO2 in the photosynthesis process in order to grow. Too much light, however, can cause problems. If your plants get too much light for instance, they will be starving for CO2. If they don’t get enough CO2, they will start to wilt and turn brown, causing algae to grow out of control.
Aquarium lighting can be confusing and quite technical, but rest assured most stock lighting that you buy for aquariums will suffice for your average planted aquarium. When you start getting into large aquariums, and reef tanks then you need to know a little about the proper lighting requirements. Mostly, you will find that the lights come with the cover and span the whole length of your tank.
Your lighting needs will vary depending on what type of plants you plan on growing, the size of your fish tank, decoration/aquascaping arrangement, the algae level in your aquarium, and how much other light is in the room. Certain live plants require up to 12 hours of light to help them grow, but if you have lots of sunshine or low light plants you may not need as many hours. Usually you will need 8 – 10 hours of light per day.
TIP: It’s best to have a timer so you stay consistent from day to day.
TANK SIZE: The bigger the tank, the more lighting you will need. Any tank more than 24” deep will need high to very high output lights to penetrate the deeper water. The higher the Kelvin rating the deeper the water penetration.
It’s recommended that your plants match the type of fish you have. Tropical plants with tropical fish and cold water plants with cold water fish. Tropical plants typically will need more light than cold water plants to help them grow. As far as the fish are concerned, the lighting is more about you seeing their colors than the benefit to them.
There are a few different types of lighting available for aquariums.
Tungsten/Incandescent lights – This is probably the worst lighting you can get for an aquarium. They burn too hot, burn out quickly, are not energy efficient, don’t show your fish colors very well, and cause algae growth. You might find these pretty cheap at pet stores but avoid them.
Fluorescent – Very popular lighting for aquarium owners because they provide an even distribution of light on the plants; they are inexpensive and don’t give off a lot of heat. Fluorescent lights are good for up to a 24” deep fish tank. They have evolved over the years from standard fluorescent bulbs to condensed, and T8, T5, T2 fluorescent bulbs. They are measured in ⅛” width increments, so a T8 would be 8 x ⅛” or 1” in diameter, T5 would be ⅝” in diameter and so on. Fluorescent bulbs typically need to be replaced every 6 months because they lose their ability to give off a proper spectrum of light.
To complicate things further, fluorescent lights come in normal output (NO), high output (HO), very high output (VHO), and power compact lights. A high output fluorescent bulb will burn about 55 watts per hour and put out about 5,000 lumens, while a very high output fluorescent bulb will burn about 95 watts per hour and has three times the lumens as a conventional fluorescent bulb or about 7,200 lumens. Lumens is the measure of light output, but not necessarily what reaches the plants. For that you need a PAR value. Power compact lights are the latest invention and use less energy to create the same amount of light. They take up less space and provide a modern, sleek look. If you have a deep tank or saltwater reef tank, then the higher output bulbs make sense. Otherwise, normal fluorescent lighting should be sufficient.
LED lights – LED is all the rage now. They are very energy efficient and offer a wide array of spectrum colors for different looks. They are much brighter than fluorescent lights as well. LED lights are more expensive up front, but have a really long life that should balance out the upfront cost over time. One great feature of LED lights is that they are programmable. You can program daylight, night time, cloudy days and run it all on auto for 24/7. You can manually adjust all of the spectrum colors as well for superior plant growth. The latest advances provide enough light power or PAR for most aquarium plants.
How Do You Know if You Have Enough Light?
Different plants have different needs when it comes to light. Some plants can thrive in low light, some plants need higher light power, and still others require really high light. What affects plant growth is the red and blue parts of the light spectrum and in what amounts.
Keep in mind there are measurements for the human eye and measurements for what plants absorb. Lighting for plants should not be chosen on color temperature alone. Kelvin temperature ratings don’t tell the whole story. Kelvin will tell you how much of the spectrum is being generated, but not what parts of the spectrum are being generated and at what strength.
Color temperature is measured in Kelvin or K for short. Kelvin is what color a theoretical black metal pot would turn at a certain Kelvin temperature. The range for aquarium lighting is between 2,400 to 10,000 Kelvin. The lower end of the Kelvin range is softer yellowish light like an incandescent bulb, while the high end of the Kelvin spectrum contains blue colors. Color rendition is measured in CRI from 0 to 100. For the best color rendition, you want about a 6,500 Kelvin light and 90 CRI or higher. For plant growth, 5500K to 6500K will mimic natural sunlight the best.
Kelvin ratings are not a good comparison measuring tool when evaluating lights. Different light sources like fluorescent and LED could have the same Kelvin rating, but will give off different spectrums of light, therefore look completely different.
Spectrum is measured in nanometers. The visible range is 400 nm (violet) to 700 nm (red). Plants absorb much of the red and blue in the spectrum, that’s why plants appear green because that is the part of the spectrum that plants don’t absorb and is reflected back to our eye. Nothing has color on its own, it’s really reflected light. If you want to optimize plant growth you need a good mix of red, green, and blue light. The green is to make the plants look natural to us.
Most important spectrum range for green plants:
Chlorophyll a: 430 nm/632 nm
Chlorophyll b: 453 nm/642 nm
Carotenoids: 449 nm/475 nm
Strength is measured in PAR or “photosynthetically active radiation.” Watts per gallon is not a good measurement. PAR strength will decrease through water and other factors like dirty glass covers. The deeper the tank the less strength of light the plant will receive at that level. Some aquarists get a PAR meter to measure this. PAR is limited in that it measures total photons in micromols per square meter per second not specific to any part of the spectrum.
Low PAR values: 15-30 micromols, CO2 not needed but is helpful to plants
Medium PAR values: 35-50 micromols, CO2 may be needed to avoid algae problems
High PAR values: more than 50 micromols, pressurized CO2 needed to avoid major algae problems.
Note: The further away the light fixture is from the top of the fish tank, the less light penetration into the tank.
Besides evaluating light for photosynthesis, you should also evaluate the lighting for aesthetic appeal. Around 6500K with a CRI of 90 + seems to be optimal for natural color enhancement because it most represents natural daylight.
LUX is a measurement of lumens/square meter. Lumens measure the light energy emitted that the human eye can perceive (green part of the spectrum), so this measurement is more for us than the plants. A light can have lower lumens, but be more beneficial for plants because of the spectrum of light being given off. A higher lumen rating means higher green light given off, which is meaningless for plants but good for the look.
CRI or color rendering index is an index of how close a light is to daylight (full spectrum) on a scale of 0 to 100. Basically, the higher the CRI, the better color rendition. A CRI of 92 is much better than a light with CRI of 80.
It’s best to have a mix of lights for both plant growth and aesthetics.
Low Light Plants: Anubias, Hygrophila, Java Fern, Java Moss, Rotala, Sagittaria, Vallisneria
Standard T5 fluorescent, or LED lights
Medium Light Plants: Cryptocoryne Parva, Dwarf Sagittaria
High output T5, LED lights
High Light Plants: Rotala Macrandra, Rotala Wallichii
High output, very high output T5 or compact fluorescent.
Low light plants are easier for beginners because they don’t require as much maintenance. The higher light plants require the most care and maintenance and lots of CO2.
Can Aquarium Lights Be Too Bright?
Yes, if you have too intense of a light for the plants that you have, you could start to have algae problems if you don’t add enough CO2. The plants may start to burn and turn brown from too strong of light.
Light Spectrum and Algae Growth
Green algae and green plants use the same pigments for photosynthesis. Light that helps one helps the other. Algae seem to particularly like the wavelengths between 500 – 600 nm. Unfortunately, many standard fluorescents have those wavelengths. In planted aquariums, the light should be strongest in the red wavelength and balanced out with blue light and some green for appearance. Approximately ⅔ in the red and ⅓ in the blue.
Regular plants are more adept at dealing with changes in light. Algae doesn’t do as well with light changes, therefore, its good to have a break with the lighting during the day. This will help curb the algae growth. Excess phosphates and nitrates also contribute to algae growth so fix your water chemistry along with curbing your lighting.
If you have green algae problems and your water is green, I use the AA Aquarium Green Killing Machine. It’s amazing.
LED vs Fluorescent: Which Should You Go With?
Really both lights will grow plants, so it comes down the look and feel you want in your aquarium.
Really energy efficient
Average life around 50,000 hours
More options as far as spectrum colors for plant growth and fish color
Nice, sleek modern look to the light fixture itself
Programmable for all parts of day/never have to remember to turn on or off
Newer technology can produce higher PAR values than before.
Can be expensive
Broader spectrum of light
Light spread more evenly across the tank
Somewhat cheaper than LEDs
Not programmable, but you can install a timer and dimmer.
Doesn’t need cooling
Warmer softer light
Are Aquarium Lights Bad For Fish?
Too much light, suddenly turning on the light or too intense of a light will stress tropical fish. Fish only need about 8-10 hours of light per day. Remember fish do not have eyelids like humans do, so it takes longer for their eyes to adjust. Check the light requirements of the species of fish you will keep. Most need a very low light at night to simulate a natural environment that allows them to sleep. That’s why you should always use a timer or programmable light in your tank.
Lighting to Enhance Fish Color
Lighting is not the only factor that affects fish color, but depending on the spectrum colors and temperature of the bulb you can bring out certain colors. Keep in mind there are lights beneficial for plants and lights that can enhance the look and color of your fish tank.
8,000K white light – Enhances orange, yellow, gold, and red colors. Promotes photosynthesis for plant growth
12,000K – Works for enhancing all colors of fish, but is especially good for reflecting silver on scales. Good choice for tetras, and most community fish.
445 nm – Good for enhancing blues and fluorescent colors. Neon and cardinal tetras, African and South American Cichlids.
Magenta and Magenta/Blue – Enhances red, green, blue, and pink colors. Perfect for live planted tanks when used with an 8,000K bulb.
12,000K white and 445nm blue – The royal blue enhances the blues and reds, while the 12,000K bright white reflects scales beautifully. Great for Tetra and Cichlid tanks.
12,000K white and Magenta – Provides stunning shimmer while enhancing reds, oranges, yellows, and blues found in most tropical fish. The magenta provides the right spectrum for plant growth.
Types of Aquarium Fixtures
Mostly you are going to find lights that fit on the top of the tank across the length with adjustable brackets. Make sure you measure your tank length to get the right type of light fixture. Lights also come as part of the cover kit, but you are limited in the choice of lighting as to what fits in the cover. You will also see lights that clip on the tank and can be positioned anywhere on the tank. These are more for smaller fish tanks as they are a source light. Sometimes people will hang the lights above from the ceiling, but I don’t see the advantage to doing that because you’re limited as to where you can put your tank and the light fixture is probably not going to be close enough to the aquarium.