Cuttings in propagator.

I'm taking woody or semi woody cuttings of mostly tender shrubs as I cut them back for overwintering.
I've had some in the propagator for a while and the easier ones seem to root OK, but I think the day length is probably holding them back from rooting now.
So I've set up a 20watt LED floodlight above the propagator in the hope of fooling the cuttings that the days are longer than they are, its on a fairly cheap timer to extend the light hours by about 3 hrs in the evenings.

Noticed something strange today, when the timer has switched the light off the LEDs continue to glow just slightly, as if the timer is still allowing some current through.
I'm wondering if that could shorten the life of the floodlight, anyone know why that should be happening?

The Timer I'm using.


And the floodlight when its switched off by the timer.

 

@pete I've noticed this with LED houselights myself and always thought it was caused by the circuitry of the power supply discharging after the mains was switched off. Mains is 240 V AC and LEDs need a couple of volts DC so some form of circuit to control the power is required and you end up with capacitors and suchlike that have electricity stored in them when you switch the mains off and then discharge through the LED over a period.
There is also often a phosphorescent layer in the LED which continues to glow for a few seconds when the LED is switched off.
These are unlikely to shorten the life.
It could also be a problem with the power supply which could shorten the life.
Sorry for the vague arm wavey response, but I've not had much to do with electronics for the past 25 years.

 

I have one that does that too - I came to the same conclusion as @NigelJ

 

Just to make it clear, it doesn't do that when its not connected via the timer, its the timer that appears to be causing it.
It also doesn't fade, it stays like it all the time when connected via the timer.

I've seen that kind of afterglow from LEDs but this is different it doesn't fade.

 

Have you got any other sorts of timers? Eg the electronic ones? It seems strange though, because that type seems to be a simple lever that hits a switch as the dial turns. So the only way it could be passing current could be if the switch is not entirely breaking contact.
Here's a daft idea. Connect the timer to a mobile phone charger. They draw small current. See if your phone still shows charging when supposedly off time.
Or get one of those non contact current detectors (always handy for checking before doing minor electrics) and wave it around.

 

The timer itself must obviously use current to turn the dial, but surely it should totally cut the current to the device.
I'll try it on my mobile phone as you say tomorrow and see what happens, I have a pen like thing for detecting if a wire is live, is that the kind of thing you mean?

Maybe I should stand in a bucket of water and touch the contacts, would that work.

 

How interesting.
Mine was also on a timer.
AFIK timers just flip the Live on or off - single pole switches.
Neutral is always connected to the LED circuitry so maybe there's some tiny residual current between that and Earth.
A double pole switch disconnects both Live and Neutral

 

I decided to ask Google - but that doesn't seem to provide a satisfactory answer

AI Overview
LEDs can continue to glow faintly when switched off due to residual energy in their internal driver circuits or from a phenomenon called ghosting caused by parasitic capacitance in the wiring. The driver's capacitor stores energy, and when the light is turned off, it slowly discharges, causing a temporary glow that fades over a few seconds or minutes. Ghosting is caused by the very small electrical charge that builds up between wires in the wall and is especially noticeable in circuits with two-way switches.
Residual energy in the driver

• LED drivers have components like capacitors that store small amounts of electrical energy.
• This stored energy keeps the LED lit for a short period after the power is switched off.
• The glow is normal and harmless, and it will disappear as the capacitor fully discharges.

Ghosting from wiring

• Parasitic capacitance:
  Wires in a circuit, especially in two-way switch setups, can act as a capacitor and build up a tiny charge, says All About Circuits.
• Inductive coupling:
  A tiny amount of current can also be induced from nearby live wires, notes Quora users.
• Dimmer switches:
  Some electronic dimmer switches can allow a small leakage current to pass through, causing the LED to glow faintly even when the switch is in the "off" position.

What to do if the glow is annoying

• Add a bypass resistor or capacitor:
  You can install a bypass capacitor in parallel with the LED to drain the residual charge.
• Use a different switch:
  A mechanical switch that completely breaks the circuit, such as a relay, can stop the afterglow.
• Install a different bulb:
  Some LED bulbs are more prone to ghosting than others. Try replacing the bulb with a different model, as shown in this YouTube video.

 

I wonder if I'm getting something similar to dimmer switches.

 

Somehow I doubt it as as CarolineL said those timers are mechanical in operation just an on off switch operated by clockwork.

 

We have one of those led lamps as a general light in the greenhouse and just tried it with a similar mechanical timer and there is no after glow.

As said there could be various causes for this effect, more so when used with a low wattage device, though unusual for a mechanical looking time switch.

Would suggest you get a diffrerent make of timeswitch , better to be safe as yours could be faulty.

 

I've used my pen thing on the cable when the switch is in the off position and it tells me the cable is still live.

Isn't that what a normal light switch does, just breaks the circuit?

 

Just tried the mobile phone idea @CarolineL and no the phone stops charging when the timer is off, but replugged the LED light back in and the LEDs glow immediately.

 

It does sound as though the timer is not cutting off all the power when it's off. Don't use it Pete, better to be safe than sorry my friend.

 

Well I'm still wondering if its an LED "thing", as as far as any other devices are concerned the power is off.