HID (Na) Light Fixture Works Intermittently

Does it have a built in temp sensor that turns it off when it starts to over heat? If so, maybe this sensor is faulty and is causing it to go on and off like you describe.

Hi, no temp sensor inside...

Does it have a photo-eye that turns it on at night and off during the day? That may be faulty. Should be a unit on the top of the lamp that just plugs in. We replace a lot more of those for every bad lamp.

Best of Luck!!

yes, already checked: it works OK:

Hello tcmtech, I did so, but the problem persists. I would not define the problem as "blinking" "Intermitent" seems to be a more accurate expression, as the lamp can be on for some minutes... or even hours, then it gets off for some minutes, and on again. Initially I thought "something" : the ballast (!!??) could overheat, quit working, cool down, start working again....

If its a magnetic type ballast its possible the capacitor is getting weak which can cause older bulbs to randomly blink out when ever there is a small incoming power dip.

As far as solid state ballasts for HID I worked at a sign company as a sign service tech for a summer and never had much experience with those other than they either worked or were burned out. I don't ever recall dealing with a half way functional one.

If they weren't on they had either had the bulb go bad or they let the magic smoke out is all that I ever dealt with.

Or the ballast is going bad. A modern HID ballast is no longer magnetic only, it is now a sophisticated SMPS (Switch Mode Power Supply), which means it has a rectifier, high speed transistor and a transformer. As it ages (or weathers) and the insulation of the transformer begins to break down, the output voltage begins to drop as windings short internally. That triggers the switch mode controller to step up the voltage, which can cause the transistor to over drive and heat up. It shuts down to protect itself, cools off, then starts up again. Repeat ad nauseum.

High pressure sodium lamps exhibit this condition called 'cycling'; as the lamps get older and reach end of life. The reason for this is that as the lamp ages the arc voltage inside the lamp increases until it reaches a point where the ballast can no longer supply the voltage and the arc extinguishes, the lamp cools, re strikes and the cycle starts all over again.

Are you able to correlate any aspects of the intermittency with any other factors, eg time on/time off with cool evening/warm evening, dry/wet, animal or insect activity ....I have heard of animals urinating on a power board behind a TV causing strange intermittent behaviour of the TV until at last the power board caught fire.....

... actually not, it started to happen randomly for a certain time, and now it is constant. thanks for asking!

These lamps operate on a similar principle to flourescent tubes; its likely a faulty ballast in the fixture that needs replacing. Hope it has a replaceable part.

Good luck

If the lamp functions in a different fixture, the problem is not the lamp (bulb). The ballast is the problem, it has a thermal overload imbedded in the windings, when excessive heat from shorted windings triggers it to open, the light goes out. When the windings cool down the overload resets it's self, and the light will come back on. Change the ballast; I have seen this problem many times.

I guess you are right..... I´ll see if I get a new one!

Change the bulb first. Most of the time it will cure it. This is normal end of life operation for this type of bulb.

r&ddoc sates in his explanation of the problem "The lamp works fine on another fixture". We can only conclude that the problem is not the bulb.

Read #5, and #7 the bulb has been changed, and the problem persists.

Then the ballast is going bad.

It is common for ballasts for HPS and Metal Halide lamps to have a thermal overload built in as has been mentioned this is to protect the windings if the unit is used at to high a ambient temperature or the designed winding temperature is exceeded due to rectifier effect,short circuit or overload . This information is marked on the choke in words or as a temperature value inside a triangle. The other thing that cause a high pressure discharge lamp to extinguish is if there is a momentary glitch in the Hz say 1 cycle possibly caused by some heavy load switching.

I did, it also happens with the new one!