Dimming fluorecent light tubes

[raitl]

Hi. I need to be able to dim fluorecent light tubes for my aquarium, as to create a more realistic day-night cycle for the fish. It could be done with a simple linear pot, but since I have 5 18W tubes, making a total of 90W, then that's kinda unpractical. And the lighting on my new tank is going to go well over 200W, so... And the reason I don't want to use the commercially available dimmable electronic ballasts, is that they cost...alot!

My current lead is: PWM controlling the rectified +350V supply of the tube... but I can't see how it could be achieved...


Any help and/or feedback would be appreciated!

 

[Nigel Goodwin]

The reason commercial dimmers cost a LOT is that it's a complicated thing to do, I don't recall ever seeing a project for one?.

 

[MrMikey83]

If its the same dimmer they use at the lecture rooms at my college, it doesn't work all that great. It may dim by half, but after that it simply gives up and turns the bulb off.
~Mike

 

[justDIY]

use more bulbs of fewer watts and time them to come on in sequence

or switch over to halogen / some other form of incandescent lighting and use a simple linear dimmer

or buy a case (25 ballasts) of 10v dimming T5HO ballasts from goodmart.com, take what you need and sell the rest on ebay

 

[Oznog]

A common wall dimmer isn't a good idea, the SCR design is not meant to work with inductive ballasts.

But the real problem is most flourescent lights can't be dimmed at all. Any scheme to reduce or PWM the current will cause one end of the tube to blacken and it will fail in a relatively short period of time.

You need to either switch off some tubes, install some sort of shade, or change to a dimmable light technology like LEDs.

 

[moody07747]

If its the same dimmer they use at the lecture rooms at my college, it doesn't work all that great. It may dim by half, but after that it simply gives up and turns the bulb off.
~Mike

in my electrical class in neptune the school is wired with dimmers for the flourescents

They are really kool and work great

 

[Klaus]

use more bulbs of fewer watts and time them to come on in sequence

or switch over to halogen / some other form of incandescent lighting and use a simple linear dimmer

or buy a case (25 ballasts) of 10v dimming T5HO ballasts from goodmart.com, take what you need and sell the rest on ebay

You may not be aware of that aquariums use special colour fluorescent lights which are just right for the plant growth and fish health. Lights such as you suggested would not do the trick.

With regard to dimming fluorescent lights, I was faced with the exact same problems when I had an aquarium. The fish would go crazy when the light was suddely switched on or off

But I did find a special ballast that worked with an ordinary switch plate light dimmer and it did the trick very well. The 20W fluoro tube would dim very low before it dropped out altogether.

Now, all that was about 30 years ago (still have that ballast somewhere :wink: though the aquarium had long since gone), I can't see any reason why these ballasts are no longer available, have you enquired at fluorescent light manufacturers?

Klaus

 

[Klaus]

Hi. I need to be able to dim fluorecent light tubes for my aquarium, as to create a more realistic day-night cycle for the fish. It could be done with a simple linear pot, but since I have 5 18W tubes, making a total of 90W, then that's kinda unpractical. And the lighting on my new tank is going to go well over 200W, so... And the reason I don't want to use the commercially available dimmable electronic ballasts, is that they cost...alot!

My current lead is: PWM controlling the rectified +350V supply of the tube... but I can't see how it could be achieved...


Any help and/or feedback would be appreciated!

I just realised that you are talking about 200W! lights. That must be one enormous home aquarium or a commercial set up.
Forget the linear pot idea - it would NOT work with fluoro's, IMO.
The ballast I used ( in the message above) looked like an ordinary ballast but there must have been something different as it was labelled a dimming ballast.
Good luck and start saving for thoes expensive electronic ballasts :wink:
Klaus

 

[stevez]

My long time pal Mike is an EE and lighting is one of his specialties. He does not design lighting controls but he does design lighting systems that use all of the latest and greatest lighting controls.

Usually he provides switching arrangements so that you can turn individual fluorescent tubes on in fixtures - to give some step control of overall lighting levels. You can purchase relatively modest cost fluorescent dimmers that will take you down to about 30% of the nominal lighting level. He said that they do make lighting controllers that will take the lighting level output of a tube down to 1% of nominal. They are incredibly expensive.

Note that wavelengths of light change as lights are dimmed.

 

[Klaus]

Hi. I need to be able to dim fluorecent light tubes for my aquarium, as to create a more realistic day-night cycle for the fish. It could be done with a simple linear pot, but since I have 5 18W tubes, making a total of 90W, then that's kinda unpractical. And the lighting on my new tank is going to go well over 200W, so... And the reason I don't want to use the commercially available dimmable electronic ballasts, is that they cost...alot!

My current lead is: PWM controlling the rectified +350V supply of the tube... but I can't see how it could be achieved...


Any help and/or feedback would be appreciated!

OK, thinking outside the square here but have you considered an electro- mechanically operated shutter? If it covers/uncovers the lights at the rate approximating sunrise/set your fish would never know the difference. You could fit micro switches that turn the lights on/off after the shutter is fully covering the lights.
Just an idea. What, you don't like it? Too bad :lol:
Klaus

 

[i_build_stuff]

https://www.electro-tech-online.com/custompdfs/2006/03/ir2156.pdf

 

[spuffock]

The secret is to keep the heaters hot ! Heaters vary with the size of the tube, but if you try a transformer of 6 volts or so to start with, you will soon get an idea of what is needed. The heater needs to be just visibly alight. Find a transformer , or 2 transformers, that keep the heaters alight.
You will find that a cheap dimmer will now dim the tube almost to extinction.
A comment about change of wavelength. This is true for incandescent lamps only.

 

[stevez]

My lighting expert would disagree on the wavelength issue. He was very specific to say that wavelength did change with output of a fluorescent tube. Since this is not my area of expertise I can only repeat what he said. He could be mistaken.

 

[spuffock]

I would be surprised. But then, I've been surprised before!

 

[stevez]

I don't understand the physics of the fluorescent light sufficiently to challenge or support his comment. An incandescant light makes more sense - reduce the voltage and it gets dimmer - and it changes color. Fluorescent lights seem to stay the same - maybe the change is much less profound. When my pal returns from his golf orgy I'll ask for a more in-depth explanation.