Energy Saving Bulbs & Time Switches.

[Mr Lawes]

I read on the back of a box of Energy Saving Bulbs, that they are not suitable for use with 'timing devices'.

I've got a couple of table lamps that are on for about five hours a day, triggered by time switches.

What would be the consequence of using Energy Saving Bulbs in these table lamps?

Thanks...!

[Christian McArdle]

It depends on the timing device. These usually work in two different ways.

The more expensive types and those with higher ratings use an electromechanical switch called a relay. These can switch most types of load, although whilst switching slightly reactive loads such as energy saving bulbs, the contact ratings are lower. This is rarely a problem, as lighting is low power and the contacts are usually rated for 13A to control heaters and the like. This design requires a neutral connection. And gets power between the unswitched live input and the neutral.

The other type of switch doesn't require a neutral connection. They run entirely inline on the live connection. This enables them to be a direct replacement for a light switch where no neutral is available. When they want to switch on, they go almost a complete dead short, and extract the energy required to run by having a tiny voltage drop. When off, they get energy by simply taking it between the two terminals. This means that a tiny current will flow through the load. As this is usually a filament lightbulb, this is no problem and the current is too tiny to be noticed. However, an energy saving bulb is a discharge tube that will not pass any current until a high voltage is presented. This means that the switch doesn't get the tiny flow of current required to power the electronics and will not work. Sometimes, the problem is even worse and the small current passed by the electronics builds up voltage in the bulb's starting capacitor meaning that the bulb will flash every minute or so. This depends on the design of the bulb's electronics.

So, whether it will work or not depends entirely upon the design of the timer switch.

Christian.

[Dave Plowman (News)]

That should have read 'with some timing devices'

If they work, none. The problem can arise with the sort of time switch that replaces a wall switch so has no dedicated neutral - relying on the one passing through the load.

Or some with an electronic 'relay' - this may not like the inductive load.

So you need the instructions for the timer - if it places no restrictions you should be ok.

If you've got the timers but lost the instructions, a guide would be whether you can hear a relay click when they switch - these should be fine.

[Mike]

But if you do have one of these, wiring a low wattage pygmy bulb in parallel with the energy saver will overcome the problem.

[Al Reynolds]

So following on from our earlier discussion about using one of these "switch replacement" timers to control a relay which in turn controls a lighting circuit, will the relay pass a small current without actuating the switch, therefore allowing the timer switch to continue operating when the lights are off?

TIA, Al

[Dave Plowman (News)]

It would depend on the relay. It might just stay on, as they need little current. If it did, you'd have to increase the current it draws by either wiring a small bulb or suitable power resistor in parallel with it.