Light dimmer

[Christopher Alexandre]

When we use adjust a light bulb dimmer, if we increase the power from the minimum, the light will turn on at a certain point. But at this point, you can decrease the light power without turning it off. I know how a dimmer work but I can’t figure out why this happend. Could someone explaine me this effect?

 

[(*steve*)]

Does this happen with bulbs that don't have a filament?

 

[Christopher Alexandre]

This happens with incandescent light bulbs

 

[(*steve*)]

One possible explanation is that the low resistance of the cold filament combined with other circuit elements that either limit current or limit the rise in current may provide insufficient heat to cause it to glow. Once the filament is glowing, it has a significantly higher resistance, and thus a given current will cause more heating in the filament. At this point it is possible to reduce the duration of the current pulses and maintain a high enough power dissipation in the filament to allow it to continue to glow.

I have no idea if this is the correct (or if it is correct, the only) explanation, but I have noticed this behaviour and this *may* be a reason.

 

[CircuitMaster]

Or if its intentional, it might be a histerezis. Like a Schmit trigger. The idea behind it is that it turns on at voltage "4VDC" (for example) and then while decreasing it turns off at "2VDC" (for example). However this only accounts for the ON and OFF, after its switched on something else regulates it. Otherwise I guess it can be some effect.

 

[BobK]

@Steve - I was thinking of the same explanation, but I saw your question and tried it out.

It does happen on my dining room light, which has all LED bulbs, so filament resistance is not the answer.

Bob

 

[Bluejets]

LED bulbs as Bob says will do this, even with a dimmer designed for general LED use.
Bit of a nuisance but just have to live with it.
I imagine there may be some underlying manfacturer reasoning but trying to find it is almost akin to flying to the moon.

 

[dave9]

Might depend on the dimmer and you could try another one? Then again, how much work to put into optimal dimming for incandescent bulbs at this point? Dimmer, they're even less efficient, much much less.

 

[duke37]

Maybe some temperature effect in the diac or potentiometer.

 

[Bluejets]

Maybe some temperature effect in the diac or potentiometer.

Dimmers are not like they used to be with a simple pot,diac and triac.
They tend now to be jammed full of electronics and anyone's guess as to what goes on in there but obviously some reason why it requires a specific level to initially turn on.
Typical LED dimmer shown below.....

 

[dave9]

^ What indication do we have that it's a new style dimmer? I would have assumed an old triac design if already in use with incan bulbs.

 

[Bluejets]

I was going by the characteristic "new LED type dimmer" mode of operation which the OP supplied.
I imagine we'll have to wait and see when they get back (if ever).