# Can I put a 17w bulb in a 20w fixture?



## Metsuke (Sep 1, 2013)

Sorry folks! I'm ignorant to the mysterious ways of electricity. Well, more or less. Uh, see, I have a 24" light fixture lying around, rated for 20 watts. Got it from a friend, it never worked, I wanted to try a new bulb and I saw these on sale for 50% off at petco~

So I nabbed one. Unfortunately, I didn't realize at the time that it was 20 watts I needed. I though they were all more or less standard outside of length. So here I am with a 17 watt bulb, and I'm wondering... will I overload it? Or is it more that the fixture is rated "up to 20 watts", and can accept anything lower?

For what it's worth the prongs appear to be identical to the old bulb. They're the same size and spacing anyway. It seems to fit just fine.


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## vvDO (Oct 18, 2010)

May help to know what type of bulb you have vs what type of bulb the fixture accepts. For example t8 or t5 or cfl? Usually if your bulb has a lower wattage rating, it should light up however it may have a shortened light. Opposite, if your fixture is rated 17 watts and your bulb is 20w it may not turn on.


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## Metsuke (Sep 1, 2013)

The only information listed on the back of the fixture is as follows:
Aquarium Equipment, Model: 36RFH. (I was unable to find any useful information with this on google).
Rated: 120 VAC, 60 Hz, 20 W.

The bulb itself has a fancy-looking H inside a circle, lists some sort of numerical code, and says "WIDE SPECTRUM 20w USA".


I have no earthly idea what T-x refers to but this fixture says nothing about it. I've got no earthly idea how to tell what kind of bulb this is. It's fat, opaque, with silver caps and dual prongs on each end. Maybe twice the diameter of the bulb I purchased.

What I purchased is a t8 "Tropic Sun 5500k Daylight" bulb, measuring 24" and 612mm, at 17 watts. Again opaque, the same length, with the same prongs. Blue caps instead of silver but I highly doubt that's relevant. Same spacing on the prongs. 

What do you mean by a shortened light? A shortened life maybe?


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## Rooster (Apr 3, 2006)

YES - it will work just fine...


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## Hoppy (Dec 24, 2005)

T8 bulbs have a lower wattage than T12 bulbs, but can always be used in T12 light fixtures, which you probably have - a fixture accepting 2 foot long bulbs. T12 2 foot bulbs are 20 watt bulbs, T8 ones are, I believe, 17 watts.


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## PlantedRich (Jul 21, 2010)

The "T" referrs to the diameter of the bulb in 1/8's of inch. T8 is one inch thick, T12 is 11/2 inch. The older style like often used in offices, etc. ?


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## vvDO (Oct 18, 2010)

It should work without issues as stated above... Have you tried it... If it doesn't work something else may need changing.


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## Metsuke (Sep 1, 2013)

Thanks guys! I didn't want to try it without some sort of confirmation. Didn't want to fry it.

Now I've just plugged it in and... I don't think it's working. The ends glow a yellowish orange, but it hasn't lit. While adjusting it, it did flash on once, but I wasn't able to get it to stay lit. 

Do you think it's maybe the fixture? Or is this normal for these sort of bulbs? I know the ancient tube-shaped bulb that lights the back porch sometimes takes as much as half an hour to light up, but I don't know why. Still, I feel like it should be instantaneous. That seems more a problem with that particular light than a typical thing.


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## mistergreen (Dec 9, 2006)

Metsuke said:


> Thanks guys! I didn't want to try it without some sort of confirmation. Didn't want to fry it.
> 
> Now I've just plugged it in and... I don't think it's working. The ends glow a yellowish orange, but it hasn't lit. While adjusting it, it did flash on once, but I wasn't able to get it to stay lit.
> 
> Do you think it's maybe the fixture? Or is this normal for these sort of bulbs? I know the ancient tube-shaped bulb that lights the back porch sometimes takes as much as half an hour to light up, but I don't know why. Still, I feel like it should be instantaneous. That seems more a problem with that particular light than a typical thing.


Yes, wrong watt bulbs can do this. It won't work. I've tried plugging in a normal t5 In a t5ho fixture and it did the same thing.


Sent from my iPad using Tapatalk HD


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## Metsuke (Sep 1, 2013)

Mmmh.. that's a shame. Oh well.


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## Rooster (Apr 3, 2006)

does it have a separate "starter"? if so try another... 

Sent using Tapatalk from my ZX81


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## DarkCobra (Jun 22, 2004)

The new bulb should work properly in the old fixture, as Hoppy described.

It could be the starter that Rooster mentioned:










Which is meant to be easily user-replaceable, as it wears out. It's usually visible just under the bulb. Give it a little counter-clockwise twist, and then it can be pulled out.

I just had a 17W T8 fixture fail in a manner similar to what you described, but in my case it was the other main part, the magnetic ballast transformer:










Which is the white (sometimes silver) part on the right. I knew it was bad because it was making a crackling noise, like something was sparking inside. I decided to replace it with a modern electronic (rather than magnetic) transformer, a Fulham Pony 10293 purchased and shipped for $8. Which fit right in to the existing mounting screws. And also doesn't require a starter, which I left in place but didn't connect.


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## Hoppy (Dec 24, 2005)

Now you know the light fixture never worked. My bet is that it is the starter.


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