Pool light went dim, then out; now replacement is dim

[rhythm]

Oh, OK...thanks! I get it now!

I guess the next thing to do is measure the voltage at the fixture when the bulb is installed and it's powered up. To do that, I'll need to get an adapter of some kind that I can screw into the fixture socket.

Thanks,
Greg

 

[JohnT]

In an earlier post, you had mentioned the continuity to the spa relay. If you look at the circuit, you'll see that the pool bulb and spa bulb are tied between their own hot and the neutral. When measuring from one hot to the other hot, you'll see the resistance of the two bulbs (and any other load) in series.

The reason I mention this is that I recall a situation I had with a piece of gear once that had a bulb intermittently dimming and behaving oddly by not coming on sometimes. It turned out to be a loose neutral. When it wasn't making a good connection, the bulb was getting current through another bulb on the circuit, but the voltage was lower than normal.

Have you measured the current in the light circuit, and have you tried turning both the spa and pool light on at the same time?

 

[CraigMW]

Greg:

Okay, so this tells us that there does not appear to be any discontinuity in the light fixture cord. 2.5-3 ohms seems a bit low for resistance on that bulb, but who knows. You can also check a standard lightbulb to see if it also dims while the light fixture is on the deck. With respect to the ground not being disconnected, that is a non-issue as you were measuring with reference to the load and neutral wires.

So, if you put a 60 or 100W bulb in the socket of the light fixture, does it work okay? Seems to me as though it should. I'm still wary about a possible thermal breaker causing problems as it heats up. What model of light fixture is it, BTW?

 

[rhythm]

John, it's interesting that you point out that issue with the loose neutral. Yesterday when I disconnected the pool light hot and neutral connections at the j-box, I noticed that the neutral connection was probably weak because the installer had stripped a lot of the strands of wire off when stripping the insulation. However, I have not experienced any on/off/intermittent behavior. Once the first bulb started going dim, it just continued to get dimmer until it was gone. The new one is doing the same thing. But for sure I'll be redoing that connection so there's more stranded wire making connection. I haven't made any current measurements yet. We have had the pool and spa lights on at the same time quite often. The spa light has always seemed OK.

Craig, I think 2-3 ohms seems low also, and I'm thinking that the bulb may have read differently when it was new. I'm going to grab a new 100W bulb from the house today and put it in there. I'm going to measure its resistance before putting it in there, and check it again after it's been on for several hours (my failing bulb only has 5-6 total hours on it). As long as I have the fixture 'open' (no glass lens and gasket installed) I should be OK with it being out of water with the light on, right? The thermal thing is interesting, because the new bulb is a higher wattage (500 vs. 400 on the original) and it started dimming very soon compared to the first one. But my initial theory is that something happened somewhere in the circuit fairly recently, and the dimming on the first bulb also happened quickly once there was a problem with the circuit. But right now, who knows? Perhaps the 100W bulb thing that I'm about to do will tell us something.

Just in case it gives any clue as to what's happening, I want to mention that the failing bulb is very dark all around the front of the glass. I've attached a picture so you can see what I mean. I've seen failed light bulbs look dark, but not like this.

Also, the light fixture is a Pentair Amerlite. I can't seem to find a model number in the owner's manual. And the fixture itself has a part number for the enclosure, but not a model number. I have the Amerlite model that goes together with a tension ring, rather than several screws all around it. I thought that the fixture housing was the exact same for the 300, 400, and 500W models, but I better double-check on that. I may have been wrong upgrading this thing with a 500W bulb. The wire size is 16 gauge I believe, which should have no problem carrying the additional amount of current, but perhaps too much heat is building up in the fixture housing. On the other hand, my older 400W bulb died the same kind of death also (dimming until gone).

I'll also mention that the newer bulb is not OEM, but rather it's a cheap Feit replacement that's actually rated at 130W, not 120.

Oh well, I'm going to connect things at the j-box again and check a few more things out.

Thanks,
Greg

 

[rhythm]

Latest info:

Before reconnecting wires at the j-box, I measured resistances of lines between j-box and control panel. Pool light hot to line connection on pool light relay, pool light neutral to panel bus bar, and spa light neutral to panel bus bar were all 0 ohms. J-box ground bus bar to panel ground was not quite, but close (1 - 1.5 ohms).

Reconnected all j-box connections. Powered up pool light and re-confirmed voltage at fixture base (reads 119.6 V). Screwed in adapter (so I can measure voltage with light installed) and failing 500W pool bulb. Powered up, voltage at fixture reads a few volts under (reads 116.4 V). I attached a picture so you get an idea of how strange the pool bulb looks when it's on. It's amazing how hot the bulb gets right away, even though the output isn't super bright.

Put a new 95W standard light bulb in the fixture and powered it up. Looks fine, voltage reads 119.2 V. It's been on for two hours now. Still looks OK, voltage is the same. I'm going to put 6-8 hours on it and see what happens.

That's it for now.

Greg

 

[JohnT]

Weird stuff, but I'm starting to think you got a bad bulb. Did the old one look like that on the front?

I've noticed a serious decline in incandescent bulb quality over the last few years, particularly in the higher wattage bulbs.

 

[CraigMW]

Yeah, I'm all out of ideas at this point, except possibly that the existing 500W bulb may have overheated. Usually, this causes bulbs to blow (when initially turned on). Seems like strange behavior for a light bulb. In any event, you should definitely be careful to not overload the light fixture. If it's not rated for a 500W bulb, then you need to back off a bit. Let us know how the 8hr test goes with the regular lightbulb you have in there. If that turns out fine, I'd suggest getting a better replacement bulb (I too have had trouble with Feit bulbs, but in that case, it was their dimmable CFLs... every single one out of 6!). Also make sure the bulb is rated for underwater use. There may be some special thermal engineering that takes advantage of the water as a thermal sink. Pentair says to not run high wattage (e.g. 500) bulbs for more that a few seconds at a time when the fixture is not sealed up and placed in the water filled niche.

As an alternative, you could also get one of those nice color changing LED screw in lights. There is one from Australia (I can't remember the name) that seems pretty cool and costs much less that replacing the whole fixture. I doubt it would put out as much light as a 500W bulb, but it might look cool!

 

[rhythm]

Final checks from yesterday: The 100W standard bulb was powered up for 6-7 hours, and still looked perfect. The voltage was still reading right at 120V also. I rigged up a long wire with some alligator clips so I could make measurements from the control panel over to the light fixture. All of the continuity checks (hot to hot, neutral to neutral, with power on and off) checked out fine. So I'm done checking the electrical stuff, and I'm thinking it's just the bulb. I didn't want to believe that because that's two bulbs in a row that have gone out the same way (dimming for a few weeks, then gone). But I can't find any problems electrically. I think I'll go with an OEM bulb this time instead of the cheaper alternative.

John, the first bulb had the same very dark look upon removal, but it was completely dead before I ever removed the fixture. So I don't know if it had that same weird orange-ish look to it while it was still alive.

Craig, I almost did the color changing LED light last time, but I was worried that we wouldn't like the brightness. I'll look into that again...I agree it would look cool! As far as the wattage in this fixture, I was under the impression that Pentair's 120V 300W, 400W, and 500W light fixtures were really all the same, just stocked with different bulbs. So I figured any of those wattages could safely be used with this fixture. I'm going to try and get a hold of Pentair and ask about this. Perhaps there's something a bit different with each fixture, and I have to stick with a 400W bulb. In any case, I think this bulb overheated also.

My plan now is just to replace the bulb and see what happens. Think I need to replace the gasket again? This one was only in use for about 8 weeks.

Thanks,
Greg

 

[Dalandlord]

My plan now is just to replace the bulb and see what happens. Think I need to replace the gasket again? This one was only in use for about 8 weeks.

If the gasket is still soft and looks good upon inspection I would put it on and just check carefully after assembly and keep an eye on it for a couple of days.

 

[JohnT]

The only expanation I can come up with for the deposits on the inside of the glass is vaporization of the filament. It would pretty well have to be overheating due to lack of cooling or overvoltage. Or a junk bulb. Just seems out there, but I guess it could happen.

 

[CoppellPool]

This post is so old, that you have probably solved it now... I had the same problem, and believe it or not, after a lot of fault chasing, I managed to isolate it to a faulty switch! the bulb was not dim when hardwired straight to the GFCI without the switch, so I replaced the switch and solved the problem. Hope this helps you or someone else with a similar problem.