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My bathroom is fitted with six traditional 20W GU5.3 / MR16 bulbs, and I want to replace them with the smart home equivalent. The only one I could find with the same socket type is the 5W Osram Smart+ GU5.3 bulb.

I bought three of them (to start with), but when I put the bulb in, and flip the switch, the bulb either flickers erratically for a few seconds, or does not turn on at all. This doesn't look like deliberate behaviour.

All three bulbs do the same, they do it in each of the six sockets, and they do it even when all the other conventional bulbs have been removed. However, with an external power source, I was able to test the bulbs, and they all work perfectly, so they're not duds, either.

The bathroom has a regular switch, not a dimmer switch.

What could be causing this issue? How do I resolve it?

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  • Tell us more about the 12V transformer, like a lot more about whether it is AC or DC, digital, age, etc. Also tell us more about that "I swear it's not a dimmer" switch -- 90% of the time it turns out it is an actively powered switch of some other kind, e.g. a lighted-when-off switch.
    – Harper - Reinstate Monica
    Commented Feb 19, 2018 at 21:23

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The most common cause of this is the 12V transformer. A GU5.3 bulb runs at 12V DC instead of normal line voltage (110-230V AC). Many transformers have a minimum load for normal operation, which the LED bulbs may not be drawing.

As an alternative, you may want to consider installing GU10 bulbs. They are the same general size and shape as GU5.3 bulbs so many fixtures are compatible, but they operate on line voltage so there is no longer a need for the transformer. You would just need to remove the transformer and replace the socket, which is a very small cost on top of the bulbs. It is the best way to negate the flickering and troubleshooting headaches.

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  • It may be that the 12V supply was run with wiring methods that are not approved for mains electricity...
    – ThreePhaseEel
    Commented Feb 19, 2018 at 13:27
  • My guess is that it's 12V because it's a bathroom; 230 volts might get a bit toasty if it comes into contact with water. Interestingly, the Osram Smart+ bulbs are marked with "12VAC", instead of DC like you suggested. Do you think that might be the issue?
    – Emphram Stavanger
    Commented Feb 19, 2018 at 20:47
  • I for one would not put 120V on pins so close together. And what TPE says about the wiring methods, you cannot indiscriminately upgrade a low voltage circuit to mains voltage. (the other way round sure, but watch your current as LV is higher current).
    – Harper - Reinstate Monica
    Commented Feb 19, 2018 at 21:21
  • Yes, I should have been more clean in my answer. You can't just change the socket at the end of the circuit, you need to make sure the circuit capable of handling line voltage safely. In many instances the transformer is in the ceiling right above the light, and paired 1:1 with each socket + bulb. This would make conversion easy. Anything in a wet area like a bathroom needs to be appropriate for that location.
    – raydowe
    Commented Feb 20, 2018 at 14:29

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