My replacement 4ft t8 strip light failed after a few years. I took it
apart and other than some slight discolouration on the driver board no
obvious reason.

I was surprised the driver was so complicated with what looks like a
transformer for a switched mode power supply and an IC amongst loads of
other discrete components and the strip of 81 leds.

Why is it not possible to use the leds across the mains input with the
sum of forward voltages equaling the mains voltage, one strip attached
live to neutral and another the other way round and a current limiter?

ajh wrote:

> Why is it not possible to use the leds across the mains input with the
> sum of forward voltages equaling the mains voltage, one strip attached
> live to neutral and another the other way round and a current limiter?

Flicker.

On 2024-03-03 13:11, Andy Burns wrote:
> ajh wrote:
>
>> Why is it not possible to use the leds across the mains input with the
>> sum of forward voltages equaling the mains voltage, one strip attached
>> live to neutral and another the other way round and a current limiter?
>
> Flicker.

It is done sometimes in quick-and-dirty, or cheap-and-nasty, low-power
lamps, where you can sometimes see a pair of strings of LEDs in opposite
polarity fed direct from mains via a current-limiting capacitor.

But flicker, and more difficult to stabilise the current with varying
supply voltage and temperature.

nib

On 2024-03-03 13:22, nib wrote:
> On 2024-03-03 13:11, Andy Burns wrote:
>> ajh wrote:
>>
>>> Why is it not possible to use the leds across the mains input with
>>> the sum of forward voltages equaling the mains voltage, one strip
>>> attached live to neutral and another the other way round and a
>>> current limiter?
>>
>> Flicker.
>
> It is done sometimes in quick-and-dirty, or cheap-and-nasty, low-power
> lamps, where you can sometimes see a pair of strings of LEDs in opposite
> polarity fed direct from mains via a current-limiting capacitor.
>
> But flicker, and more difficult to stabilise the current with varying
> supply voltage and temperature.
>
> nib

Flicker. Does anyone else notice how LED lights can split up into dashes
if you move you head quickly? It's quite noticeable to me, especially
with car rear lights in the dark, I can often tell if they are
continuous or pulsed.

As a spectacle-wearer, I have another way of checking, effectively using
the retina as a sort-of oscilloscope - I just waggle the lenses rapidly
in front of my eyes. Continuous lights, like an incandescent, show as
smears, pulsed sources as a series of dashes. You can even estimate the
frequency and mark-space ratio!

Anyway, back to the original topic. I have an ancient plug-in LED, the
very first I bought, many years ago, which is about 100 small LEDs
arranged in a shape reminiscent of a pineapple. The waggle test shows
that is flashing right on an off. That is one that I know is just a
capacitor dropper from the mains. It lives in the bathroom where its
crudeness is not important.

nib

On Sun, 3 Mar 2024 13:11:56 +0000, Andy Burns <usenet@andyburns.uk>
wrote:

>ajh wrote:
>
>> Why is it not possible to use the leds across the mains input with the
>> sum of forward voltages equaling the mains voltage, one strip attached
>> live to neutral and another the other way round and a current limiter?
>
>Flicker.

Would you get flicker at 50Hz? I have to say I've done this and can't
notice any, but that might just be me.
LEDs are "currrent orientated" devices so your current limiter would
need to keep the current through the chain at 20mA (or whatever each
LED is rated for).
There are potential dangers with doing this, however. I wouldn't
recommend it to someone unfamiliar with electrical safe tea.

On 03/03/2024 17:41, Cursitor Doom wrote:
> On Sun, 3 Mar 2024 13:11:56 +0000, Andy Burns <usenet@andyburns.uk>
> wrote:
>
>> ajh wrote:
>>
>>> Why is it not possible to use the leds across the mains input with the
>>> sum of forward voltages equaling the mains voltage, one strip attached
>>> live to neutral and another the other way round and a current limiter?
>>
>> Flicker.
>
> Would you get flicker at 50Hz? I have to say I've done this and can't
> notice any, but that might just be me.

Definitely. Where LEDs are driven at 50Hz, without smoothing (such as
the red and green men on some pedestrian lights), I get a horrible,
momentary strobe effect as I drive past or turn my head while waiting,
giving multiple very short lasting after-images.