On Wednesday, 4 December 2019 14:39:46 UTC, Dave Plowman (News) wrote:
In article ,
pinnerite wrote:
On Sun, 01 Dec 2019 19:46:43 +0000, rick wrote:

Been fitting new kitchen .... one of the last job was fitting 3 new
hanging lights. in and working (well sort of)

Wife had bought LED 'filament' decorative bulbs ...... they work fine
on full power or can be dimmed ... but not turned off .....
Dimmer is type you press button it dims to off .... with theses bulbs it
dims to off and then back to low.

First off thought dimmer was faulty - but put in some standard GLS bulbs
and it works fine.

After searching specs it does say non-dimmable (but not in advert or on
packaging)

I'm going to have to find dimmable LED .............. but what makes an
LED bulb dimmable or not ?

I find the dimmables do not start from zero luminance but some way up.

Even where you alter a plain LED via the amount of current passing through
it, can be difficult to get a smooth increase from zero. But easier to
reduce to zero smoothly. I'd guess they need some sort of start up kick.

Well they are called diodes and that means getting above the threshold which is noramlly 0.6V to 0.7V for a silicon and 0.3V for gernamium but as yuo had things so you get colour I guess that changes things.

if you take a basic LED they typically don't start conducting below 1V

And it;s easy if yuo start from the LED being ON and then slowlty turn it off as you'll still get a bit of persistance of vision from the eyes, which will mask the delay in turning an LED from OFF to 1V to it's conducting voltage.