Bathroom bulb only giving off weak light

Question

I turned on my bathroom light this evening and was surprised to note that it only gave off a very feeble light, barely illuminating the room. On inspection, it looked like only the ends closest to the connection were giving off any light at all.

I presumed this was a bulb issue, so I changed it and was surprised to find that the new bulb behaved identically. So it seems this is an electrical fault.

The light fitting takes 4 pin fluorescent bulbs, like this: https://www.amazon.co.uk/Philips-PL-Q-GR10Q-Compact-Lamp/dp/B000ONNOH4

The issue only affects the bathroom light, and no others in the house. I have not noticed any other electrical faults, nor am I aware of anything that might have caused a wire to break or become lose anywhere.

What might have caused this? Is it something I can fix, or do I need an electrician? Is it urgent, in the sense of it being a safety hazard?

Answer 1

Fluoresent ballasts do go bad. If it is a very old fixture it may have a starter:a starter is usually a small tubular module with 2 pins on 1 end - a twist, usually CCW, and it will come out. Starters used to be very common; if you find one it is probably bad. If no starter, the ballast has failed (not uncommon).

Changing a ballast is a simple procedure: turn the power off, open the fixture and record the part number on the existing ballast. Find one online or locally. Usually there is a line diagram of the connections. If you get a different brand, you may need up to 6 wire nuts: again with the power off, cut the black and white at the ballast and connect to the new ballast. Next is the lamp connections - many mfr's use the same color-coded wiring. If the wires on the old ballast match the new one, finish cutting the old ballast out and wire nut the wires together. If the colors are different, compare the line drawings on the 2 ballasts and transfer to the new ballast using the diagram on the old ballast. This is what electricians do.

I have changed thousands of ballasts over the years and I still need to look at the instructions. Ballasts are a DIY item in my professional opinion.

Answer 2

For a fluorescent lamp to function, it needs a device called a "ballast" that boosts the household voltage up to a higher state, which then "excites" the gasses in the tube into a plasma, which then causes the white phosphor coating to "glow" with white light. The excitation of the plasma takes place only at the ends of the tube on some electrodes. When a fluorescent tube "dies" it's because those electrodes basically deteriorate to the point of not functioning.

In your case because you swapped out the bulb with a (presumably) new one and the problem persisted, it points to the ballasts having failed now. the voltage it is putting out is too low to fully excite the gasses in the tube, so that dim glow is just the electrodes, something you don't normally see because the other light is so much brighter. As a general rule I don't recommend changing a ballast out yourself if you are not VERY competent in electrical work, it's a "call the electrician" job.