I have a small aquarium that has been illuminated so far by a 15W fluorescent lamp. The problem is that the ballast has broken (melted) after 2 years of use, and the only replacements I could find on my market (same, 1x18W) break after 1-2 hours of use. By "break" I mean they heat up, start melting, stop working. The melting always happens at the coil, which by the way looks just like a transformer, and probably is one, but only has 2 wires connected to it, while the second pair remains in the air (see attached photo).

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So, lacking any viable solution using classical fluorescent tubes, I thought about 2 options:

  1. Find 2 sockets and install them, so they would fit 2 9W compact fluorescent lamps. But:
    • Are the built-in compact ballasts able to handle a relative humidity of ~70-80%?
    • Can they work in relatively closed spaces where temperatures might rise to up to 50 degrees Celsius (because of the energy output) during summer?
  2. I have a remarkably rich assortment of LEDs on my market, that is totally lacking fluorescent tube lighting accessories. So I thought about using LED lighting, but:
    • I've read that they are less efficient than fluorescent tubes, so I'd need then about 20W LED
    • 20W LED would make even more heat, and where would that dissipate? Especially that I've read that LEDs work best below 40 degrees Celsius. I can find lots of single high power LEDs, and combined LED lamps, but the high power LEDs have no accessories to them, no radiator, no nothing.
    • I'm afraid of the "warm" light spectrum. I have plants that need UV light, and light sources that focus on "warm" light usually cut down on the blue and UV light, while fluorescent lamps peak at UV.

Maybe another option:
Is using a ballast with more power going to help? Or is that only going to fry my tube, while the cheap electronics inside the ballast is as likely to melt as the less powerful one? When I've read what ballasts do, I figured that since they are built for, say, 40W, then they would maintain a higher Voltage*Current for the lamp. Or is it actually a possible solution to my problem?

  • \$\begingroup\$ I'm guessing they wanted an inductor but the transformer was cheaper, so they just used one of its coils. \$\endgroup\$
    – Polynomial
    Dec 6, 2013 at 15:10
  • \$\begingroup\$ Are you using a 40W ballast on a 15W lamp? \$\endgroup\$
    – Phil Frost
    Dec 6, 2013 at 15:16
  • \$\begingroup\$ No, I'm using a 18W ballast on a 15W lamp, but so far the last 2 ballasts lasted for 1-2 hours, so I was just thinking about other options. \$\endgroup\$
    – Alex
    Dec 6, 2013 at 15:20
  • \$\begingroup\$ @AlexanderMP Well, that sounds like your problem. Ballasts are design for specific lamps -- you can't just mix them and expect them to not melt. \$\endgroup\$
    – Phil Frost
    Dec 6, 2013 at 15:23
  • \$\begingroup\$ Well the lamps on my market, in this range, are 15W only. The first ballast, that lasted for ~2 years, was also 18W. I'll ask a supplier of course, if you say that 3W can cause such effects, but I doubt that I'll find compatible parts in this power range. \$\endgroup\$
    – Alex
    Dec 6, 2013 at 15:27

1 Answer 1


Plenty of cool white (and straight UV, if you like) LEDs are available (and the cool types actually have better lumens-per-watt efficiency than the "warm" types, as a general rule.)

Lumens-per-watt efficiency is all over the map, so you have to check the particular LEDs you are considering using. Some are awful, some are quite good.

Cooling is something you'll have to sort out, especially with high power LEDs, where thermal design is most of the design work. Stock aquarium hoods are terrible for it, so most folks with serious lighting setups end up building something that allows the lamps to cool more effectively (may involve a fan, may involve a barrier between the water and the lamp which will slightly reduce light into the aquarium, but greatly reduce humidity at the lamps, etc.)

One factor you may have missed is that the LEDs drive all the light towards the water, where the florescent has considerable losses from the parts of the lamp where light is reflected before hitting the water. I have 8.9 watt LED ceiling fixtures which are undeniably brighter than 13 watt CFLs for exactly this reason, even though they are "only" 70 lumens per watt.

  • \$\begingroup\$ For the purposes of aquarium plant lighting, lumens-per-watt is a poor figure of merit, because the definition of "lumen" is weighted more heavily around green light, most of which is reflected from plants, and not photosynthetically active. \$\endgroup\$
    – Phil Frost
    Dec 6, 2013 at 15:50
  • \$\begingroup\$ It is, however, the only one you're going to get on most datasheets. There are some delightfully purple (blue, red, very little if any green) plant-growing LEDS out there, though. \$\endgroup\$
    – Ecnerwal
    Dec 6, 2013 at 16:07
  • 1
    \$\begingroup\$ Anecdotal note: our tank uses a mixture of white LEDs and low-intensity UV LEDs for this purpose. It gives the same result as a CFL but is significantly more energy efficient, safer (lower voltages), and seems to have a better lifetime. The model up from it has white, warm tinge (yellow) and cool tinge (blue) LEDs that cycle throughout the day to emulate daylight, along with the UV ones. It was rather more expensive, though, and I doubt goldfish would appreciate the subtle nuances of simulated daylight. \$\endgroup\$
    – Polynomial
    Dec 6, 2013 at 16:34
  • \$\begingroup\$ Thanks for your advice. I decided not to go with LEDs. I've removed the ballast and the tube holder from the tank roof, and placed CFLs there instead. It was very easy to install them, and cheaper. It has been working without a problem since. \$\endgroup\$
    – Alex
    May 6, 2014 at 10:09

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