4' light into 18" light

[familyman03]

Okay so I have access to many 4' 4 bulb flourescent light fixtures (the ones in your kitchen). What I want to know is if I can take the light "guts" and shorten it to run at the 18" size. Do I need a special ballast to do this or just pull the old one apart and put onto my hood. Also what is the best way to reflect the light into the tank if I do this it will sit on the wood of the hood and i want as much light into the tank as possible. Will a ballast set to run 3-4 lights at 17-40watts run 3-4 lights at 15 watts. Is there anywhere I can buy 30 watt 18" lights that are not yellow.

Thank you Jason

[fishykid1]

you can...but why...? I'm taking it your talking about a t-12. Which I don't believe comes in a 18" size.. but who knows. This one is puzzling, why not just buy an 18 inch strip light, or even stop by homedepot and pick up just a single t5 24" light. bulbs would be cheap.

[lauraleellbp]

Originally Posted by familyman03

Okay so I have access to many 4' 4 bulb flourescent light fixtures (the ones in your kitchen). What I want to know is if I can take the light "guts" and shorten it to run at the 18" size. Do I need a special ballast to do this or just pull the old one apart and put onto my hood. Also what is the best way to reflect the light into the tank if I do this it will sit on the wood of the hood and i want as much light into the tank as possible. Will a ballast set to run 3-4 lights at 17-40watts run 3-4 lights at 15 watts. Is there anywhere I can buy 30 watt 18" lights that are not yellow.

Thank you Jason

Check out ODNO threads in the DIY forum to see if that will work, but my gut feeling is that it will be easiest just to buy some new ballasts or a retrofit kit. I'd probably upgrade to T5s rather than sticking with T8s anyways- they're much more efficient.

You put a highly polished aluminum reflector behind each bulb to reflect light down into the tank.

You want a bulb with a higher kelvin rating. If you don't want to bulbs to look yellow, look for bulbs that have a kelvin in the 8000-10,000 range. 8000 will appear more green, and 10k will appear more white. Personally, I like running a combo of different bulb spectrums- 6700k, 10k, mixed in with some pink bulbs (Colormax, PowerGlo, etc). IMO that's a great way to bring out ALL the colors in a tank.

[xmas_one]

I say go for it! You can use the 5000K and 6500K bulbs at HD or Lowes. Be advised though, that the bulb life will be shortened quite a bit, you'll get 6 months out of an overdrive like that. Check out the ODNO threads lauralee suggested as well. Keep us posted.

[familyman03]

Originally Posted by fishykid1

you can...but why...? I'm taking it your talking about a t-12. Which I don't believe comes in a 18" size.. but who knows. This one is puzzling, why not just buy an 18 inch strip light, or even stop by homedepot and pick up just a single t5 24" light. bulbs would be cheap.

well what i am doing is i have pulled down a 4' fixture with t8 lights and want to reduce it for cost effective reasons to fit ontop of my 28" wide tank and to use the bulbs that i like and have had success with

[nokturnalkid]

Most newer electronic ballasts will drive a bulb that is shorter and less wattage of the same diameter. It's usually written on the ballast. Since this fixture was a prebuilt one, there may not be any label on the ballast stating what it may actually handle. Chances are though, you will be fine using all the guts of your old fixture. Do this at your own risk since I'm no lighting expert.

[S&KGray]

Originally Posted by familyman03

well what i am doing is i have pulled down a 4' fixture with t8 lights and want to reduce it for cost effective reasons to fit ontop of my 28" wide tank and to use the bulbs that i like and have had success with

If your tank is 28" wide I would shorten it to fit 24" bulbs not 18" bulbs.

Btw, do you have any pics of the fixture you are working with?

[Hoppy]

Just some musings: The voltage drop on a tubular fluorescent bulb is proportional to the length, or should be, based on my experience with other arc or discharge type electrical devices. So, the voltage for a 4 foot light is a fixed number. Therefore, the ballast must restrict the current to a constant value, to arrive at 40 watts. In other words it probably is a current control device. If that is true, smaller tubes with lower voltage drops should be driven at the same current. 48 inch tubes are 40 watt, and 24 inch tubes are 20 watt, so they are very likely driven at the same current. Based on that I would expect a 4 foot light ballast to work with 24 inch lights almost exactly the same as with the 4 foot lights. Undoubtably it is more complicated than that, but I still think it will work fine.

[chad320]

I dont have all the technical advice that hoppy does but I have done it and it does work and if you replace the bulbs itll grow plants for at least 5 years from my experience.

[familyman03]

Okay so I took some initiative and went down and bought two dual bulb 4' shop lights for 9.96 apeice and the four bulbs I would need. Here is how it turned out. So for a total of about $20 I got what I would say is the equivilant to 120 watts of light instead of the original 30 watts. I think they turned out wonderful let me know what you think

[Hoppy]

Looks like you did a great job! Congratulations.

[jinx©]

Wow, I guess the pictures say it all. Good job.

[nokturnalkid]

Nice job.

[S&KGray]

Very nice!

[dbosman@msu.edu]

Good job and thanks for posting pictures. Several times people have asked about shorting fixtures. Your post with pictures should help people in the future.

A bit of advice from a flourescent "modder" or over driver, when shopping for most anything, keep an eye out for bulb bargains.
Over driving shortens the life of a fluorescent tube. Getting bulbs by the case makes over driving a real bargain for me. While I've seen, and purchased 24" lamps/bulbs by the case, I've never seen a case of 18" lamps.