LED Bulbs installed on a circuit with a timer are flickering

Customer Question


I have bought some 9W e27 led bulbs from you for indoor and indoor use.

Indoors they are fine, as well as some outdoor fixtures (ip rated).  However, when applied to some of the fixtures outdoors, they flicker continuously when not turned on.  Do you know how I can solve this problem?  They are used in some traditional outdoor lantern lamps.



Technical Tim

Thanks for the communication and sorry to hear you are having a spot of bother; a most unusual issue and one we have not come across.

If you could supply a little more detail we’ll do our best to assist to resolve the issue.

a) How many exterior lamps do you have?

b) Are they all the same type?

c) Is there just one switch to turn the lamps on/off or can the lamps be turned off from more than one position?

d) What is the distance (approximate) between the lamps?

e) Is it the farthest or nearest lamps that have the issue or is it random?

f) Does the issue stay with the lamp or the lamp socket? Change the lamp and see if it makes a difference. If the flickering stays in the same location it is possibly the socket/wiring issue, if it goes away it is possibly the lamp. Note we say possibly, there are complications.

g) If you put a standard filament lamp in one position does the issue go away?

h) The flickering, can you describe it a little further please? Flickering is the lamp(s) continuously illuminated whether at full or reduced level with a fast or slow variation in perceived brightness. Flashing is the lamp fully off, with a period of illumination (brief?) followed by an  off period, t e process repeats. If it is flashing do the lamps flash at the same time?

Thanks for your help and look forward to receiving your response.



Here are my answers to your questions:
a) 12

b) yes, but some are on timers set from an internal on/off switch with a timer built into the switch
c) on and off from only one switch

d) width of our front door (standard size)
e) it seems to only happen on the lights with the timer on the switch

f) if I change the bulb to a normal filament bulb, the lights do not flash
– if I change one of the pair of lamps (controlled by one switch) to LED, and the other to a filament bulb, the lights do not flash
– if I change both bulbs to LED, then the lights flash
g) yes

h) I mean flashing (the issue only occurs when the lights are off). When the lights are on, there is no flashing
– flashing occurs very briefly, less than 0.5seconds, but there is no pattern, the flashing seems to be irregular
– the flashing occurs at the same time

One more question, what is a LED GLS bulb? I’ve seen them elsewhere on the internet. What does the GLS bit mean?


Technical Tim

Thanks for the comprehensive information.

GLS is General Lighting Service a term that refers to the “pear shaped” lamps we are all familiar with and originally was used for the glass/tungsten filament versions that generally had a lifespan of around 1000hrs, now in the process of being totally phased out be EU edict.

In response to your information and if I have read an understood correctly the issue is only with the lamp(s) that are on a timer circuit and not those that are switched on/off via a traditional switch.

I suspect that the timer switch is not of the older electromechanical switching relay type, they haven’t been around for a fair few years and you can usually hear a mechanical noise as they  operate, but will be one that uses the more modern type of electronic switch, possibly a triac. You will probably find that the design of the switching circuits in the timer is intended for resistive loads such as the tungsten filament of the GLS type only and not intended for inductive loads such as CFLs or LEDs, there may have been a note with the timer saying not for CFL loads.
In particular with LEDs and the main reason for using them, their very low power consumption, the electronic switch in the timer unit will allow a small amount of leakage current to flow even in the time off position. This leakage current will be sufficient over a period of time to charge up fully the electronic power supply in the LED lamp and cause it to flash the LED on. The flash will exhaust the stored energy in the LED lamp power supply and the process will repeat itself ad infinitum; the timing is dependent on a number of factors.

Isolating the power to the timer will prove the point. With power removed say via an isolator switch to the timer the lamp will cease to flash.

The reason the timer unit circuit functions correctly with a tungsten GLS unit in circuit is that the tungsten filament represents a virtual short circuit for the “leakage” current. The current is insufficient to power the GLS lamp either on its own or in the pair I think you have and similarly even with one tungsten GLS and one LED in circuit, the filament of the GLS unit removes the power source so that the LED unit is deprived of energy.

This effect will apply to practically all LED lamps that have a safety isolating switched mode power supply in them as ours have.

If this is the case as I suspect, then the best solution I’m sorry to say is to replace the timer unit with one suitable for inductive loads and particularly low power ones.

I trust this assists you and I hope I have understood your particular installation and your explanation, however if you require any further information or assistance please do not hesitate to contact me.

Regards and thanks

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