Home Repair

Outside flourescent mogul bulb

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I have an outside light controlled by an electric eye, dawn until dusk.
The bulb is of a "Mogul Type" that is a 65 watt flourescent no ballast.
I guess that this means that the ballast is in the light fixture itself.
My meter tests 120 volts on the line side before the electric eye.
My meter tests a few volts after the electric eye at the socket. I am assuming that the photo sensing eye has failed although I'm not sure what I should be reading when there is a ballast involved. The Mogul Flourescent Light bulb has a stamp written on it 120v 65watts. How can I test the bulb, out of the fixture, as I have no working fixture to screw it into. A standard light fixture using a standard incandesent bulb, controlled by a photo sensing eye, would be easy to narrow down the problem compared to this situation.
I am assuming the fixture is stuck in the off position, and you'd like the light to come on manually? Or are you looking to prove it's the sensor?

You could turn off the power to the fixture, run an alligator clip across the photo sensor connections, and turn the power back on and see if you've got a circuit. I am assuming from your description that it's normally closed and that light opens the circuit.

If though, the light sensor is supposed to generate a couple of micro-volts to act as a signal to another circuit, the 120 volts on one side of it could signify a faulty circuit (short) elsewhere and jumping across could hose it further (not that a fault like that is probably cost effectively repairable, anyway) and/or melt your alligator jumper.

Have fun and be careful and safe!
There are two types of ballasts, magnetic and electronic. I will assume because of its age you have a magnetic type. ALL magnetic ballasts have the tell-tale humm or buzz. All this testing is for the magnetic type ballast. A ballast is hard to test... sometimes. When they go, there is usually a tell-tale sign, like brown goop oozing out or the label is charred from overheating. If it looks OK then test with a meter.

You can use a volt meter to test. The ballast has to be tested with the power off by checking for continuity in the filament windings. There will be a very high resistance to ground for each filament. Don't try this with the power on!

You can ALSO test by checking voltage (Make sure you set your meter to AC and to around 700volts) across the Red & White wires (usually is red & white for a one bulb system but the white could be yellow). There should be around 600V (yes that was 600) and micro volts across the other leads.

OR just replace the entire fixture! The ballast, sensor & bulb will cost more to replace than an entire brand new fixture!
Since writing I have found that the bulb can be purchased at Home Depot for about $15.00. The entire fixture can be replaced, and it comes with a bulb for $40.00. I plan to put the meter away, purchase the new unit, and call it good and will probably end up with money left in my pocket compared to the time to diagnose. But it is kind of fun to know what makes things tick. By the way there was no inline switch, you know one of those cheapy jobs. So I have to go to the breaker panel and start the ole turn off and on game. What good service person would install a light, no matter what kind, and not put in a switch ? I don't believe that that cheap fixture would have a magnetic ballast. By old, I meant 5 years.
There was no hum when power was present.
Well good luck with the replacement.

You will find out weather it has a magnetic or electronic ballast when you open it up to yank it off the wall. Magnetic ballast is big, ugly and heavy. The electronic ballast is small and light. The magnetic wouldn't hum if it is bad anyway.
It may not hum when there is power applied to it, but maybe I can get a couple of moans out of it if I lay it on the ground and beat it with a large sledge hammer. Will let you know !


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