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Compact Fluorescent Pin Arrangements – Common Aquarium Lighting Questions

Hi, this is Ahmad. I have worked in customer service and periodically on the sales floor at That Fish Place for more than 10 years. I have received countless questions from customers over the years, but questions on lighting lamp bases and Compact European/straight pin arrangementFluorescent pin configuration are very frequent. Some while ago, Dave provided insights on the meaning of Kelvin ratings, which is also a source of confusion for lighting customers. This blog aims to answer some questions with concern to pin arrangement on Compact Fluorescent Lamps.

CFLs are popular for use on freshwater, saltwater, and reef aquaria, and even for use in our homes (those energy efficient, coil-shaped bulbs). Compact Fluorescent technology provides a cooler running, more efficient, more natural light that will last much longer than traditional incandescents and fluorescents.  Most of you who run CFLs on an aquarium have externally, electronically ballasted compact fluorescent lamps. Electronic ballasting allows more precise starting and stopping and an efficiency increase of up to 10%. Most of the Compact Fluorescents that we sell consist of two parallel fluorescent tubes, though they may contain up to four tubes. They are joined by a plastic connector on one end. The connector has metal pins which plug into your lighting fixture. A common misconception is that each tube on the CFL is a separate lamp. Unlike the way traditional fluorescent lamps are designed (a single tube with connector pins on each end), the parallel tubes of the CFL form a single lamp with a single connector.

Compact fluorescent lamps for aquarium applications usually have either European (straight pin arrangement) or Japanese (square pin arrangement) style connectors. How to tell what you have is really simple. European style lamps have four pins in a straight line. Japanese style lamps have the four pins in a square or box-shaped pattern. Other, less common varieties include PL, PL-S 2P and PL-S 4P. Thes are all straight-pin type lamps – “4P” stands for 4 pin, and 2P stands for 2 pin. So long as the lamp you are selecting is of equal or lesser wattage, the pin arrangement is the same and the length is about the same (keeping in mind that some manufacturers include the pin in their measurements and some manufacturers round their length measurements), the lamp should work.

Hopefully this blog addresses some common and easily answered lighting questions. If not, feel free to ask away!


  1. avatar

    I’m curious about what replacement options are out there for the red sea max 130d tank, which comes standard with 55w 10,000k dual actinic lighting. I don’t think the lighting is powerful enough, as the corals are stretching for more light, and i can see the light intensity is not penetrating down into the tank. The overall hue is too white as well. I’ve seen some blue actinic lights in the 55w range, but don’t see the k value or know if they would positively change the look and growth of the corals. Anyone know of an LED kit for the Red Sea Max? I know there’s a lot for nano tanks, but nothing for red sea max that i found..
    Appreciate anyone’s help on the matter..

  2. avatar

    Graham, There are no LED retrokits available for the 130max tank that is going to be a significant upgrade in light output vs. the original 55w power compacts, at least not with some significant modification. You could fit a couple Panorama modules and stunners inside the available space, but I would not reccomend adding any LED inside with the power compacts, they put off too much heat.
    You can also get a 65w straight pin PC bulb that will work in your max tank, that will get you a little more light from your existing setup, you can get them in the 50/50 type you have now or pure actinic.


  3. avatar

    I have a 20 Gal. high tank with the standard 12″ X 24″ opening. I have one of those “old school” light fixtures that is designed to sit on top of the clear glass section of the aquarium hood the front panel folds back for access to the tank and the back has pieces that can be popped to allow access for equipment such as filters and heaters and stuff. I am having difficulty finding a replacement bulb on the “That Pet Places” web site. The fixture is 23″ inches long but the bulb itself(including its TWO prongs) is 18″ long. Can you tell me what size bulb I should be looking at and if I can’t acquire the proper size at that pet place could you recommend another retailer that might be able to help me?

  4. avatar

    I need 10,000k 55W Square Pin Power Compact Bulbs. I do not see where anyone carry’s the 55W anymore.
    Is the 65W the current replacement bulb for the 55W?

  5. avatar

    Hello Ron, The availability and selection of fluorescent fixtures and bulbs in general has been decreasing over time in favor of more efficient LED fixtures. I wouldn’t say that one is necessarily replacing the other as opposed to the selection simply becoming more streamlined, but if you have a favorite manufacturer, that would be a question to ask them directly.

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