17 Apr 2006

Green Switch Off

Our house is designed with a walk-in pantry. How very now, I hear you thinking. Only it’s never quite been the wonderful place I thought it might turn into. It’s not a spot the kids choose to hang out in on a Tuesday evening, or a venue to discuss village gossip with a neighbour. It’s just a plain old storeroom, stuck across the utility room at a somewhat annoying distance from the main kitchen area. You have to avoid dogs, washing and odd bits of hardware spread across your path to get into the pantry, so it’s a sort of inconvenient convenience store.

It is lit by a single bulb. No architectural lighting features here. There are no windows, just a breeze hole at the far end, so without the light being switched on it’s really a bit desperate in there. Being a family with three slobby boys, the light was of course always being left on, sometimes overnight. Now, as a paid up member of the grumpy-green tendency, you can imagine just how my blood pressure would head up off the scale when being confronted with a light left on overnight.

Three years ago, I hit on a plan. I pitched up an electrical wholesaler one day and bought a time-lag switch. Maybe you’ve seen them? Instead of flicking a switch on or off, you press a big button inwards, the light comes on and then slowly the button works itself back out to the off position and the light turns off when the contact is broken, after a time delay of a couple of minutes. The time delay is adjustable. They are dead easy to fit – the slip into a regular switch backplate with the same electrical screws. Great idea, but how would it go down?

I snuck in and did the job with the aid of a torch (there being no light available whilst I changed over). It took maybe three minutes. Then I sat back and waited for howls of protest from wife and/or sons. “What have you done to the bloody light switch, you twat” or some such family bonhomie. But the funny thing is the protest never came. I think they actually liked the light switch. Once the novelty of a push-in light switch had worn off, we grew to enjoy the way it worked. There is a somewhat pleasing, sensual quality to being able to push a light switch inwards. More biological than mechanical. Maybe it was to be a small green success story?

Well yes and no. About six months ago, the switch started sticking in the on position and on a couple of mornings I found the pantry light on and the push-in switch in a state of permanent depression. Now, far from being an energy saving device, it was in danger of becoming an energy waster because it’s not easy to turn the light off, if it doesn’t do it itself. You have to tug at the button and persuade it to start its outward journey. It misbehaved two, maybe three times and then it seemed to fix itself. Or so I thought.

Then last week, I was rummaging round in the vegetable rack, just next to the switch, and accidentally knocked the switch with a bag of parsnips. The push button popped out of its socket, rolled across the shelf and came to rest on the floor. The light immediately went out, so I picked up the push-button and stuck it back in its hole, and pressed it in to bring the light back on. Voila! It wasn’t broken after all! Thinking how clever to get that fixed so easily, I got the onions I was after and went into the kitchen. Then, two minutes later, I heard a ping followed by the clattering sound of the push-button hitting the floor again.

The switch still works but every time it reaches the off position, it comes loose from its moorings and pings out across the shelf. I’m buggered if I can work out how to fix it. I put a wire basket underneath the switch to catch the push-button before it falls on the floor, but it’s not what I’d call an ideal solution.

So tonight, I went on line to the TLC website and ordered a replacement. They are called Time Lag Switches and they cost around £15. I wonder if the replacement will fare any better than the last one?


  1. When I got around to removing the face plate, I found out just why the unit had stopped working. There was a tiny brass screw, designed to hold onto the plunger, which had come adrift. I was able to fit it back on with my fingers so the switch is now operating as designed once more. Plus I now have a spare one!

  2. AnonymousJuly 05, 2006

    Whilst many of us are weighing the advantages and disadvantages of solar power and GSHP its good to see that you are leading from the front with your pneumatic switch, Mark. Mind you I think that your approach to adopting pneumatic switch technology was somewhat reckless.

    You should have done a cost benefit analysis to see if there was a reasonable payback (a cost benefit analysis is that thing people do to confuse the green issue with the money issue). So, I did it for you. There were some very complex calculations involved in estimating the time the light was actually being left on under the pre-pneumatic regime. Surveillance in your pantry revealed the answers:

    You didn't say what size bulb your pantry uses: I assumed 70 watts.
    Visits to the pantry per 24 hours: 25
    Average duration light being left on (mins): 8
    (sometimes just 1 minute – sometimes much longer)
    Light left on overnight: once per week
    Overnight means 720 minutes

    Means light on 25 hours per week - 1300 hours, in a year.

    Including the fact that each bulb lasts around 1000 hours (at a cost of 40p for new bulbs every 1000 hours thats 0.50p per year for pantry bulbs) it cost you about £7.36 to run the light for those 1300 hours each year.

    Under your post-pneumatic regime the light is left on for only 2 minutes each visit (assuming your pneumatic button is set up that way) and never overnight. This reduces the time the light was on to 6 hours per week, or 300 hours per year.

    Including again the fact that each bulb lasts around 1000 hours (at a cost of 40p for new bulbs every 1000 hours that's less than 1 bulb per year for pantry bulbs – 0.12p in fact) so in total its costing you about £1.71 to run the light for those 300 hours each year.

    Unfortunately your pneumatic light switch cost about £15.00 – but I am afraid I doubled it because you actually bought two – owing to some surprisingly shoddy electrical work undermining your first installation.

    I did a Net Present Value analysis for each cash flow (using a discount rate of 4%) and it turns out if you sustain the pneumatic regime for five years you will break even. The present value of the cash outflows of the pneumatic regime, when sustained for five years, is £30.71. The net present value of the cash outflows for the same period of the old regime would have been £32.76. Basically the annual savings of £5.64 recover the costs of £30 for two pneumatic button switches very quickly. So, I guess that you were lucky – given that you didn't do this analysis before rushing down to the shops?

    Personally – I think you should have installed an infra-red detector, to activate the light when someone enters your pantry (although your bill might be affected by mice).