Bulbs Electric Life of

I have been asked to repair the red tabernacle lamp in our church. The church was re-wired 5 years ago and when I was asked to see why the lamp wasn't working, I was horrified. An unswitched cable enters a flying (Because it was draped over the back of wood panelling) junction box which houses a transformer (Uneathed) where the shellac covering has partially dropped off. from this, a piece of flex is attached to the output side by cloth insulating tape which makes its way to the brass tabernacle lamp. Here the flex changes to some thinner wire (Selotaped joint) and passes up the bracket to a 12 volt screw in torch lamp. The socket is home made from what looks like plaster of Paris.

Ok, so I can mount a socket onto the unswitched manis cable (isolating the supply first) and then provide a double insulated transformer, and re-wire the brass bracket and terminate the bulb end with a new ceramic G4 socket (as 12 volt screw in bulbs are more difficult to find than G4 2 pin halogen bulbs.

Tabernacle lamps are illuminated 24 hours a day (Perhaps why there was no switch for the supply).

I want to reduce the brilliance of the lamp and propose using a 6 volt output transformer and that seems bright enough.

Question is, what sort of bulb life would I expect from a 12 volt 10 watt Halogen bulb.

Should I look for something better (The old screw in bulb probably lasted for 10 or 20 years !!)

Should I just see if I can find a small screw in bulb and leave it at that.

If I used a LED array replacement bulb, it would be too bright.

Ideas please.

Bob

It's old technology but it might be worth trying a neon lamp, which may not give exactly the colour you need, but it should last a long, long time and consume very little power. ( mains voltage so may not be safe, depending on location.)

Rod

Maybe some low wattage christmas tree lights wired in parallel would give the required light output. Having a number in parallel will allow one to fail and leave the rest on. Regular checks would allow the failed lamp to be replaced so a constant light is maintained.

Martin C

In my experience LED's always lasted a lot longer than incandescent lamps. I would be thinking along the lines of a standard LED (not high brightness) and maybe use a translucent shade or 'envelope' to decrease the brightness more, if required.

I expect some of the electronics guys here could describe a good solution, perhaps with a dimmer circuit.

Ed.

Have you considered a car/motorcycle bulb, with appropriate lamp holder?

Clem

Halogens are designed to run at a particular voltage and too many or too few volts reduce their lives.They also run hot and are inefficient. An ordinary incandescent bulb like a car sidelight would be better or perhaps a LED on a suitable dimmer.

Most lamps last longer when run dim and switching on and off is what bumps most of them off. An under run bulb that's never switched off could last for decades.

Dave

S O D is right, what shortens the life of filament lamps is the current surge at switch on, (when the filament, being cold has minimum resistance )

Overunning shortens life tremendously. Photoflood lamps are / were 110 volt lamps running on 240 volt mains. They gave tremendous light, with a high colour temperature (relatively ) but at the -expense of a very short life. The life could be extended by switching on with a dropper resistance in series to limit current. I used a 150 watt mains lamp in series for start up, shorting it out when the Photoflood was glowing nicely. Extended the life so much that none ever blew!

Under running a lamp will extend the life very greatly. It will also reduce the colour temperature from the blue end of the spectrum towards the red. Q H lamps may not work so well on reduced voltage, since they rely on the high temperature causing the filament to vapourise and to recondense. Run at a lower temperature, they may not run hot enough to function as designed, and might just behave as a normal filament lamp, possibly even less effectively or as long lived.

I would explore using an LED lamp,possibly slightly under run. The current consumption is going mto be minimal, probably 3 watts or less. Ideal for a continuously "burning" light.

Howard

+1 on using an LED, of course you should probably look in Digikey or other electronics supply places to get one with high reliability and longest possible life. I have seen the better ones listed in such places as 50,000 hour , or 5.7 years continuous operation guaranteed life. Only a dollar or two more than the cheapies. Using a cheapie would definitely be a transgression in this application.

Anyway as to brightness there is no reason you could not use a dark plastic filter sheet or two over/around the LED to block some of the emitted light to dim it, while letting it run at design rated current for best life. In this case it may be needed to hide one's light under a (semi transparent) bushel. (sorry)

Any ex phone charger wall wart power supply would work for powering it, if output V and I were what the LED required. Just food for thought.

You could use an LED and a circuit from this website to control the brightness :

**LINK**

Stuart

You could try a carbon filament lamp, not too bright, and will last

Bert

With all the 'soft' fabrics you describe about there is no way any 'high energy' filament lamp should be used.

LED way to go.

Here is an intresting thread about light bulb history Light Bulbs

Why can't an old-style incandescent light bulb last for a century's continuous use? Some can. The explanation may surprise you. See "The Light Bulb Conspiracy - Extended Version" **LINK**

Don't worry, it's not loony conspiracy theory nonsense, but a sensible documentary. Unfortunately, it may raise your blood pressure to dangerous levels. It explains a lot about why much of what we buy fails far too early.

Edited By Kiwi Bloke on 25/07/2020 11:20:06

There is a MBC 12v halogen lamp which is 6W, number is HW6/Bax95, used on some of the more exotic cars, as front sidelight bulbs, under-run at 6V should last a very long time.

Edited By Chris Shelton on 25/07/2020 12:24:34

Filament type Christmas lights are designed to be 'over-run', operating at a very high temperature which gives great light output, a brilliant sparkly effect, and a short life ensuring a good trade in replacements. When the traditional 'olive cone' bulbs became difficult to get I sacrificed one twelve-light string and used it to extend all the others to 15 lights. Since then - over ten years ago - I have had almost no failures, and having laid in a stock of spare bulbs when I could still get them, I have a lifetime supply which will keep my heirs and successors in fairy lights for generations to come, even though they are no longer made.

The 'more recent' (last fifty years?) olive cone lamps have an internal device which short circuits the bulb when it fails, which makes it easy to identify a dead one in the series string. Previously one had to take out and test each bulb individually which took for ever. However, it does mean that they are seriously unsuitable for single or parallel use, as they would short-circuit the power supply on failure.

Personally I would favour a suitable, under-run filament bulb for this application, because it gives a more pleasant and omni-directional light than the alternatives.

George B.

The best LED lamp I have found is rated at 30,000 hours which is about 4 years life - Hardly fit and forget. As others have said (And why change a proven system) back to a 12 volt "torch" bulb - just replace the transformer for a double insulated transformer (not a wall wort thing) with a 6 volt output.

thanks for the ideas.

Bob

A door bell transformer should fit the requirements.

John

The cost of the wasted electricity with an incandescent lamp will dwarf the cost of an LED once even every couple of years and a decent switch mode power supply will beat (almost?) all transformer installations. An incandescent lamp and transformer would help to keep the place warm.🙂

Sod is correct on halogens.

For a simple solution I suggest a LED rear red sidelight bulb either run off a lower voltage or with a series resistance to reduce the brightness. Reducung he brightness in this way will increase the life significantly.
Personally I'd make up a lamp of several individual 5mm LEDs and resistors, running them well below rating.
A norml mains transformer and rectifier will be more reliable than a switchmode, power supply. Again over rate it e.g a 15VA transformer for "5W" LED sidelight.

Robert G8RPI.

Edited By Robert Atkinson 2 on 25/07/2020 16:30:11