Design voltage of incandescent lamps

As is well known, the nominal or declared voltage of UK low voltage mains was reduced from 240 volts down to 230 volts, some years ago. Nothing much actually changed though and the measured voltage still tends to be 240 volts most of the time in most places.

But what  is the design voltage of mains voltage incandescent lamps for the UK market ? is it 230 volts or 240 volts. Is the light output and service life measured at 230 volts or at 240 ?

If a lamp designed for 230 volts is burnt at 240 volts the life will be significantly reduced.

If a lamp designed for 240 volts is run from an actual 230 volt supply, then the light output will be significantly reduced.

Incandescent lamps are now much less used, but there is still a substantial market via a number of loopholes. Traffic signals still use incandescent lamps.

  • Amazon/ebay/Temu are remote selling into the UK and a lot of the products sold do not meet a BS or BS EN standard.  Some may say they are selling poor quality items.  If you are looking for lamps for the home Ikea are quite good quality and units last a fair while.  Another point to note is an incandescent is totally electrical where as an LED is electronic. 

  • The Designers will need to work on it longer until

    it is fit for purpose and fit for peer review.

    Too many products come to Market before they are ready for the Market.  eg AFDDs

  • Which is why where things really matter, we often have the equivalent of incandescent lamps longer than you might like, such as a telephone standard with voltages and current levels based on carbon granule microphones and moving iron earpieces, with complex electronics at both ends emulating the original kit. Or, if it is a railway telephone, sometimes the actual original kit.


  • Yeah I'd rather an LED but when you've got a lamp that's got an older dimmer then the electronics need current flow through it - because there's no neutral connection in the dimmer. So unless I do something radical I can only use incandescents - or halogens.

    Even if I replaced the dimmer, dimmable LED's operating of mains are just embarrasingly poor - especially for a reading lamp. Maybe I'll wrap some dim to warm tape around a tube and install a driver. But that would probably look very heath robinson.

    I can't be the only person with this problem - it's clearly widespread and has been for over a decade - but nobody can find a good solution.

  • I have used a low wattage transformer for 12-18V as an autotransformer to prolong the filament life in such case - primary on the mains, of course, and the secondary in anti-series (opposition) to the mains, to give mains in less the secondary  voltage.
    Its smaller/ easier than the variac, and less heat than the resistor.

    Though a resistor may be better in some ways as it actually limits inrush too.


  • Could try and speak to company like JCC and see what they have to offer.  Realistically you need to match the lamp and the dimmer to get the best effect. 

  • Its not just the lack of neutral - because the LED light power supply starts with a bridge rectifier and a capacitor, the dimmer sees a very odd current waveform, and indeed at the moment the triac firing circuit triggers, there may be no current at all if the cycle has yet to reach a voltage that exceeds the smoothing capacitor voltage so the bridge is not yet conducting. Repeated firing pulses to the SCR do help,  but makes for a very current hungry dimmer - far more then the normal R/C + diac that we normally get that gives one firing spike per half cycle. Changing between leading edge and trailing edge may help, but you still need the dimming device to be turned on and stay on, when there is not yet any load current, and yet to go off at the voltage zero crossing.

    In many ways, the cheaper non dimmable  lamps that are a capacitive dropper, plus a few caps in a box, work much better.


  • Its smaller/ easier than the variac, and less heat than the resistor.

    Yeah I was thinking variac simply because I have one under my desk.

  • hah I detect a fellow traveller.

    You don't keep ferric Chloride in a bottle under the sink by any chance? There are similar points on the hardware geekscale to be earnt by having a lathe at home, and the combination of a lathe and mini-mill is a point multiplier.


    PS I'm teasing and not at all saying that is a bad thing - I can claim a Variac (20A model, from a skip dive) the ferric chloride (and the HCL to spike it when it starts to fade), the lathe and a small bandsaw, as well as 2 scopes, spec an and  VNA and 2 RF sig gens.

  • You don't keep ferric Chloride in a bottle under the sink by any chance?

    There's a limit to what my wife lets me keep in the kitchen. But a few things in the fridge which are clearly labeled up as not for eating. I try to minimize harzards at home for obvious reasons.