Lighting either a Planted & Reef Tank – Frequently Asked Questions


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  1. Do I have enough light for my tank?

It is important to have an adequate amount of light for your tank, and you can’t expect the aquarium fixture you buy to come with one. If you aren’t sure whether or not you have enough light, you probably don’t.

  1. How much light is required for my planted tank?

The amount of light you need for your tank depends on a number of things, including the size of the tank and the plants you will be growing. Tanks that are between 20 and 75 gallons should have at least 2 WPF (watts per gallon).

  1. What does WPG mean and how do I calculate my WPG?

WPG stands for watts per gallon and it is a way of measuring how much light you have in your tank. To accurately calculate your WPG, you will divide the total number of watts you currently have by the number of gallons your tank is able to hold.

For example, a standard 55 gallon tank usually comes with two 18 watt bulbs for a total of 36 watts, or just one 40 watt bulb. If you are calculating for the first example, it would be 36÷55=0.65 wpg. If you are calculating for the second example, it would be 40÷55=0.72 wpg. If you have a 55 gallon tank, you will need about 110 watts of lighting. Keep in mind that WPG is based on fluorescent watts and US gallons. Since this measurement is also based on T12 lighting with standard reflectors, you will be able to use more recent technology for better lighting without quite as much light.

  1. Can I use incandescent/halogen lights in my tank?

While it is true that some people have had success using incandescent/halogen lights in their tanks, they are more effective at heating than providing adequate light.

  1. What do the terms “Kelvin” and “color temp” really mean?

Kelvin is used as a way of measuring the color temperature of light. Click on Kelvin for more info. What is really important is that you understand that lights that are in the 5000k-10000k range are most effective for plants. Most people will see plants under 5000k lights as being very yellow looking, while plants under 10000k lights can appear blue. Many of the best bulbs for planted tanks fall within the 6500k-8800k range. GE manufactures a 9325k bulb that is extremely popular with those who have planted tanks.

  1. If I have three 3000k bulbs, do I have 9000k?

No, because Kelvin is measured cumulatively, meaning that is you use three 3000k bulbs at the same time, you have 3000k light.

  1. Are actinic lights good for plants?

There is still no clear answer as to whether or not actinic lights are healthy for plants. A lot of people believe they don’t do much for plants, so I wouldn’t recommend using them. If you have already met the basic light requirements for your tank, you can feel free to use actinic light. Some reports suggest these lights cause algae growth.

  1. Will putting in quality reflectors increase the amount of light in my tank?

No. Reflectors cannot actually produce light, but good ones will get more light into the tank and could reduce the overall amount of light you have to use.

  1. What is the difference between a T12 and a T8 bulb?

When it comes to fluorescent tubes, each “T” is equivalent to 0.125” or 1/8 of an inch. So a T12 bulb is 1.5” in diameter and a T8 bulb measures 1” in diameter.

  1. What’s a PC or CF bulb/light?

A T5 bulb is a bulb that measures 0.625” or 5/8 of an inch in diameter. These bulbs have become increasing popular and they offer an efficient way to light your tank.

  1. What is a T5 bulb/light?

A T5 bulb is a bulb that measures 0.625” or 5/8 of an inch in diameter. These bulbs are also becoming very popular as they can light a tank very efficiently.

  1. What’s a MH bulb/light?

A MH bulb is a metal halide bulb. These bulbs are very powerful and best suited for reefs, but they are a bit too much for just planted tanks.

  1. How long should my lights be on?

You should keep your lights on anywhere from 8 to 10 hours, but there are people who run them as long as 12 hours each day.

  1. Can I leave my lights on longer to make up for inadequate lighting?

Absolutely not. Doing this will not work and it could lead to algae growth.

  1. I have a 4’ long tank. Can I just use a shop light?

You can use any type of lights you want, but it is important to keep in mind that shop lights are not designed to work in most or humid environments like inside of an aquarium. Shop lights are also designed to illuminate large areas and not a specific small area, so they are not more than 60% accurate for this purpose.

  1. What is ODNO?

ODNO stands for Oven Driven Normal Output. This is a method that is used to get as much light as possible out of standard fluorescent bulbs than what they are intended for. While this method does work, it does come with the potential risk of electrical shock and fire. If you want to learn more about these lights, simply Google “ODNO lights”.

Author: Tristan Gordon VIEW ALL AUTHORS POSTS

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