Automatic switching of low energy bulbs

[Handyman]

A certain well-known online supplier of electrical items states on its website that its low energy bulbs are unsuitable for use with dimmers, time switches, or photocells.

Dimmers I can understand, but I can't understand why they are saying that you can't use them with time switches or photocells. Surely it makes no difference how the power to the bulb is turned on and off?

I want to use low energy bulbs in photocell-operated security lights.

 

[bernardgreen]

A certain well-known online supplier of electrical items states on its website that its low energy bulbs are unsuitable for use with dimmers, time switches, or photocells.

True, the lights often flash when they are turned off by a time switch or light sensor.

Dimmers I can understand, but I can't understand why they are saying that you can't use them with time switches or photocells. Surely it makes no difference how the power to the bulb is turned on and off?

These have a circuit across the switch contact which protects the contact from arcing. But it also allows a minute amount of power to by pass the switch when it is turned off. For incandescent lamps this power is so small the lamp filiment is not affected. But in low energy bulb this small amount of power builds up in a capacitor until it is enough to light the lamp. With one short flash the stored power in the capacitor is gone and the lamp goes out. But the capacitor starts to charge up again. Put a small incandescant bulb in parallel with the low energy and the flashing will not happen.

I want to use low energy bulbs in photocell-operated security lights.

Not a good idea as they take a while to come up to full brightness. But mix a low energy and a incandescent and you get the best of both worlds. And with two bulbs if oe fails you still have a security light

 

[Handyman]

Excellent answer, bernardgreen. Thank you.

My one manually switched low energy bulb comes up to full brightness in less than a minute. I am fitting 4 additional lights opearated by one photocell, so I will make one of the bulbs an incandescent version.

As a matter of interest, why is it that you can buy low energy bulbs with a built-in photocell?

 

[bernardgreen]

Take care with the loading.

Some low energy bulbs have an in-rush current at switch on that is quite high, looks like a high wattage for about 1/20 of a second. This may shorten the life of the switch in the sensor.

Depends on the make but a rough guide is to use 10 times the wattage of the low energy lamp when adding up the load on the sensor.

 

[Handyman]

Just went and looked on the box. Switch is rated at 1000w (more than enough), and, lo and behold, it also says "suitable for use with low energy bulbs" (I should have looked there in the first place ), so may be I don't need to include an ordinary light bulb?

 

[Spark123]

You won't

 

[Steve]

Fit a low-energy bulb at the top of your stairs and watch it flicker when apparently switched off!

Bernard I suspect you're confusing photocells and PIRs. The fact that low energy bulbs take a while to reach full brightness isn't a problem if they're on all night

 

[breezer]

I fitted a pir (separate) with an eyelid light from screwfix, it has a cfl, takes about 2 seconds to get to max brightness

 

[bernardgreen]

Fit a low-energy bulb at the top of your stairs and watch it flicker when apparently switched off!

Bernard I suspect you're confusing photocells and PIRs. The fact that low energy bulbs take a while to reach full brightness isn't a problem if they're on all night

Yes I was confusing the two. To me a photocell is a break beam detector and the thing that looks for darkness is a solar sensor.

( I must give up being a non conformist )

 

[securespark]

Fit a low-energy bulb at the top of your stairs and watch it flicker when apparently switched off!

I have and it doesn't!

 

[breezer]

likewise 75 watt one

 

[Handyman]

I've been trying to get some 'de facto' answers to this from various suppliers, and the answers I'm getting are entirely inconsistent, misleading, and in one case, rubbish.

For example, one company said that low-energy bulbs should not be used with photocells because they turn the lights on and off a lot, which they don't like, but it was OK to use a timeswitch. Well, my photocell goes on at dusk and off at dawn (I hope) with a 9 hour gap. Whereas, I could programe a time switch to go on and off every 2 minutes. So where's the logic in that company's advice?

I'm going to use my photocell to switch low-energy bulbs, and be done with it.

 

[RF Lighting]

If you get a proper zodion photocell you will have no problems.

IFAIK it is the magic eye types that can cause problems.

 

[Adam_151]

The answer is that some of these automatic switches (be they PIRs, time switches or dusk/dawn sensors) switches use electronic switching, and at least the cheaper ones will have been designed with the understanding that they'll not be connected to a load that isn't 100% resistive

When you connect them to a circuit that doesn't have a pf at unity you get some undesired effects, as previously mentioned the transiants switch on currents can kill them off (semiconductors are very sensitive to overcurrents), also the shifted waveform can casue the electronic switching to 'stick' on (basically the current flowing in it needs to fall to zero for it to be able to switch off), we can fix this problem with a 'snubber' however that worsens the third issue which is semiconductor switches sometimes 'leak' a bit across them which can cause the famous 'flicking landing light' effect in CF lamps

Get a device which pulls in the load via a mechanical contactor for rest results (do check the contacts are rated for reactive loads tho!)