• Alison Hodge
    88
    This has been asked elsewhere so I am reposting here.

    'Has anyone experienced a strobing effect with stripy sallies and bright overhead lights? Just had new bright lights fitted and concerned that if it is a real strobe effect it could have implications.'

    This phenomenon is probably what we mention, with a caution, in our document on tower lighting that is on the CCCBR website. https://cccbr.org.uk/wp-content/uploads/2020/02/SM_Lighting_2019_Ver_3.pdf
    from this webpage https://cccbr.org.uk/resources/stewardship-and-management/

    The strobing is visible as a result of physics and similar to what is described here: https://en.wikipedia.org/wiki/Wagon-wheel_effect
    It is not just related to brightness of the new lights.

    Some people are more sensitive to this strobing effect, some seriously affected. The contractors who installed the lighting should a) have been advised of moving striped sallies before the contract was placed and agreed, and b) should now recheck that the lighting installed has the correct technical specifications for use with movement such as with the sallies going up and down.

    You are wise to raise this and it should be looked into by the contractors.

    Note that in churches appropriately registered electrical contractors should do the work as explained by one insurance company here https://www.ecclesiastical.com/documents/church-electrical-wiring-guidance.pdf
  • Philip Pratt
    16
    With the greatest respect to most electricians that do valuable work in churches, most, if not all are not lighting designers and not skilled in the selection of light fittings, just like the ringers and the clients (PCC). Whilst electricians have the experience of putting light fittings in, they are rarely the ones that look at or use them so generally do as instructed on the back of their purchase order from the PCC.
    The cause of flicker is generally the lighting rectifier circuit within the driver behind the LEDs and its ability to smooth out the ripple on the rectified AC mains voltage to generate DC. Whilst LEDs are common in everyday life nowadays, the ones without flicker are more likely to be the professional products that come with a much better LED driver at a much higher capital cost. One of the big advantages of professional fittings is that they have a lot more literature about them and can provide flicker-free assurances or a quantifiable amount of ripple. The cheaper LEDs won't have been tested, and are likely to have a ripple many times worse than the ones that have been tested.

    I have come across a couple of ringing chambers at towers that have not long been re-hung, where the lighting level is akin to "restaurant mood lighting" at best. There seems to be an underestimation of the amount of lighting required.

    From a technical perspective, as it is the driver at fault in these LEDs causing the flicker, it is entirely practicable if the LED fittings allow their internal one to be bypassed, to fit a much better driver upstream, or local to the LED fitting. Some of the professionals LED drivers will output 230, or even up to 300VDC, which would mean you could drive the fitted (mains powered) LEDs direct from another driver without any work to them, and the rectifier circuit within will never see an oscillating AC supply. I have not looked into the cost of this, but I suspect the professional quality LED drivers could be greater than the cost of some of these LED light fittings that are suffering from flicker.
  • A J Barnfield
    127
    Tungsten bulbs used to be ok. Just had to plug them into the socket.
  • Simon Linford
    152
    On my visit to Kingsteignton recently they had a large rectangular panel light in the ceiling which looked like a daylight simulation LED lightbox.
  • Alison Hodge
    88
    ... and did that cause the visible strobing? Or perhaps you are not sensitive to the effect - not everyone is. Also was there some daylight or was it dark outside?

    It may be an industrial standard specification unit installed there, as we recommended. Perhaps also they had single colour sallies - it is only striped multicolour sallies that will cause the strobing, and some colour combinations may be more problematic than others.
  • John de Overa
    72
    This is a known problem with LED lighting, and is usually a function of cost - cheaper = more flicker. The only realistic fix is to change to lighting to something that's adheres to a low-flicker standard, but that's inevitably going to be more expensive than some cheap no-name LED fixtures.

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