Slightly OT. Heat and a Bench Light ...

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I usually use circular fluourescent lamp of an anglepoise inspection lamp for bench illumination but sometimes use a traditional one (Luxo for those over there). In that I have a 60Watt one that is conical in shape, like Apollo earth lander capsule, that has silvering on the cone so directs both heat and light forwards unlice dichroic which is designed to pass heat through to the rear and light forward. The cover gets about as hot as something less than a 40W standard bulb. They may be used for shop display purposes these silvered bulbs. As most of the rearwar light is directed forwards more efficiently than a cluttered white cover then perhaps equivalent to standard 150W illumination in the direction where you want it

The ones I have are coloured but I scrape the varnish off the front, Endon Accessories Reflector R080 type

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

I'll have a look for some. Without any desire to re-open the CFL thing again, I currently have one of those in it, as it was all I had to hand. The light from it is useless in this application ...

Arfa

As far as appearance, like a bayonet version of the leftmost one of these

Perhaps 80 percent of the rearward cone is silvered, so reflecting that part forwards, both heat and light.

Anglepoise is one of my favourite made-up words, precisely giving its mechanical function , unlike Luxo which could be anything involving light. If the workroom gets too hot I have an 6 inch fan mounted on the anglepoise arms of an ex-light.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

Arfa Daily Inscribed thus:

Don't count on the lampholder being undamaged ! The springs in the holder that apply pressure to the contact pads on the bulb, weaken with both age and heat. It would be wise to replace the lamp holder.

Yes the smaller glass envelope does increase the heat considerably ! The bulb produces a little more light as well. I don't know that being lead free makes a lot of difference, the heat sure does though !

Yes I agree, overheating is a problem. I enlarged the vent holes on my desk lamp for that reason. I used a nibbling tool that I bought at Radio Shack when I was in the USA a few years ago.

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Best Reagrds:
                        Baron.

I've got a CFL in mine - but not an ordinary one. It's an RO80 substitute made by GEC and a genuine 100 watt equivalent, but only 20 watts or so. Decent colour temperature too. Takes a wee while to come up to full output

- but not a problem for this sort of use. The price may be, though. ;-)

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*Always drink upstream from the herd *

    Dave Plowman        dave@davenoise.co.uk           London SW
                  To e-mail, change noise into sound.

The lampholder is ok. Oddly enough, I renewed the cable to the lamp a few weeks ago, as it had gone intermittent at one of the bend loops, and as the holder was original, and looking a little worse for wear, I put in a new one, and a new pressel switch as well, which had failed and been bypassed long ago ... :-)

Arfa

As I understand it (possibly wrong), the higher the temperature of the filament, the more efficient the incandescent light bulb in lumens per watt. There's a bit of a clue at:

During ordinary operation, the tungsten of the filament evaporates; hotter, more-efficient filaments evaporate faster. Because of this, the lifetime of a filament lamp is a trade-off between efficiency and longevity. The trade-off is typically set to provide a lifetime of several hundred to 2000 hours for lamps used for general illumination. Theatrical, photographic, and projection lamps may have a useful life of only a few hours, trading life expectancy for high output in a compact form. Long-life general service lamps have lower efficiency but are used where the cost of changing the lamp is high compared to the value of energy used.

In other words, the newer smaller bulbs are trading efficiency for lifetime, which is the result of running hotter. I'm not sure why the bulb is smaller. My guess(tm) is that it's simply thicker, which allows the use of a smaller bulb size, which can withstand the heat better than a thin bulb and can handle a higher internal gas pressure (which is necessary to prevent filament evaporation).

More on the subject:

--
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

Yes ! The middle one. The original cable was fabric woven sheath over rubber. I replaced it with "electric iron" cable but that didn't last as long as the original one. I've now got a modern plastic insulated cable in there. Its much thinner and more flexible. I used cambric spaghetti over the wires at the bulb holder end just in case the heat damaged the plastic insulation.

That little push on push off switch went a very long time ago ! There is just the hole now, adding to the ventilation !

--
Best Regards:
                     Baron.

I too have a thin plastic cable in there. There was a good reason that I changed it apart from the intermittency. Over the years, it has had a lot of 'half-arsed' repairs done to it. I'm sure if you have one, you know exactly what I mean. It's half past two, and the guy is coming to pick up his amplifier that you have assured him will be ready at half past four, and the bench light starts going on and off ... Well, a long time ago, some silicon sheathed heat-resistant wire had gone into the lampholder, and been joined to the feed cable (via the pressel switch bypass ...!!) with a bit of plastic choc-bloc. Yes, I know, but I didn't have a ceramic one to hand.

Anyway, it had been fine until I started using these small very hot bulbs in it, whereupon the nylon insulation on the bloc had crisped up. Well, a couple of weeks ago, I had one hand on the (earthed) chassis of an amp I was working on (no, it wasn't plugged into the bench isolation tranny as it should have been !) and I grabbed the Anglepoise shade to pull it into a more convenient position. A microsecond later, the air turned blue as a stream of profanity flowed from my mouth ...

The crisped up insulation on the choc-bloc had left a mains leakage path to the metal shade. I decided there and then that no such thing was going to happen again, so I have now rewired it with a thin three-core cable, and grounded the metalwork to mains earth, via the earth connector on the brass lampholder. Silicon sleeving has also been fitted to the wire ends in an effort to proof them at least some, against future heat problems.

I've got to admit that the shock I got from the setup was a bit of a wakeup call, as it's often the case that your forehead brushes agains the lamp shade, as you try to stick your head inside some recalcitrant item that's on the bench for repair. At least now, if there should be any future leakage issues, it should just whack the RCD out.

Arfa

Interesting thoughts. Really not a good thing though, I am thinking. It's only been a matter of a few months that I have been using these small bulbs, and they have already caused a problem with a lamp that had previously been running daily, without heat-related problems, for years. It seems to me that in certain domestic applications, these could represent a significant fire hazard. Take for instance, a 'standard' pendant room light fixture, suspended on normal plastic cable. There is not normally enough heat generated, to cause a problem with the insulation, but I'm sure that with the increased temperature that these things run at, there's going to be.

Take also, a typical lampshade made from either plastic or paper based sheet. These will typically have a sticker in them saying something like "60 watt max lamp". Now that figure is a fire safety one, based on the heat generated by a typical 60 watt bulb. What about when you put one of these new ones in ? I would guess that the heat steaming off them, is at least equivalent to what you would be expecting from a traditional-sized 100 watt bulb. So even putting in a correctly rated 60 watt bulb, you could be thermally overloading that shade, by 60 odd % . Potential fire hazard, or am I just being paranoid ? Does this need bringing to someone's attention ?

Arfa

You might have a point, however I find it odd that you're using a 75 or 100 watt incandescent bulb in a desk lamp. I have a few here and they all specify 60 watts maximum. I guess that applies only to the old large bulbs.

This is probably what's happening:

Yeah, looks about right.

Wanna disclose the maker and model number of the hot bulb?

Candle flame = 1700 C Match = 2000 C peak

100 watt bulb = 2500 C

Are a few degrees C going to make much of a difference? I don't have the proper IR thermometer necessary to measure such high temperatures. See if you can beg or borrow an optical pyrometer used in a steel mill or foundry, you can measure the temperatures. Forget about using thermocouples as they don't cover the temperature range:

Meanwhile, use an IR optical thermometer to measure the temperature of the lamp shade, to see if it's ready to ignite. Compare the old and new bulbs. A few measurements will tell you if you're in danger of burning the house down. Judging from the description of how a Halogen bulb works, I suspect you have a justifiable concern.

--
Jeff Liebermann     jeffl@cruzio.com
150 Felker St #D    http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann     AE6KS    831-336-2558

Ooo shudder !

I must admit I don't plug mine into the isolated side ! Doesn't/didn't yours have an earth connection then ? Mine does and had one from new !

I've seen electric heaters repaired with those plastic choc-blocks put in them. I once had an old lady ask me to look at one. She said it smells funny and there is something dripping out of the back. The plastic surround had almost compleatly gone and the connections were hanging in mid air. I had a go at the guy who repaired it and was un-politely told to sod off........ Sadley there weren't the consumer protections in those days !

Its a good thing you didn't touch it with your forehead ! I can't imagine the possible injury it could have caused. At least it shouldn't happen again.

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Best Regards:
                     Baron.

I don't know about Arfa's lamp, but mine never had any warnings about bulb size ! I do know that at a pinch you could get a 150 W bulb in there. Indeed on the odd occasion I have done just that. Interestingly I recall that the light output was actually poorer with the bigger bulb. Probably because the filament was considerably further away from the shade/reflector.

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Best Regards:
                     Baron.

There's no difference from a choc block than any other screw connector - like those found in sockets, etc. Make a poor connection or use an incorrectly rated one and it *will* give trouble.

--
*Certain frogs can be frozen solid, then thawed, and survive *

    Dave Plowman        dave@davenoise.co.uk           London SW
                  To e-mail, change noise into sound.

One general thing to be aware of these Anglepoise lamps. Well the stronger , older , all metal ones. Make sure all the little rubber grommets are present and correct, not perished, at each of the channel holes that the mains cable passes through.

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

If it's old enough it will have silk covered rubber cable too - which perishes.

--
*What was the best thing before sliced bread? *

    Dave Plowman        dave@davenoise.co.uk           London SW
                  To e-mail, change noise into sound.

I couldn't agree more !

However I was referring to the fact that some Id10T had replaced the original ceramic terminal block with a plastic one ! The fact that the plastic over the course of a couple of weeks had just melted away with the heat, rather than just a bad joint. Its likely that the original had one or more seized or broken grub screws, leading to its replacement.

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Best Regards:
                     Baron.

Yes mine did ! That was one of the reasons that I used cotton braided electric iron flex as the first replacement. I found it less durable than the original.

--
Best Regards:
                     Baron.

I was a little concerned that these would not still fit, when I put the 3 core cable in, but they did, just fine.

And to Baron. I've had the thing a long long time. It's an orange one that came from BHS originally, but a genuine Terry's Anglepoise, none-the-less. Before that, I had the even earlier one with the black 'flying saucer' shade. I can't remember what happened to that one. Over the years, it has had much work done on it, but I'm pretty sure that it never had anything other than a 2 core plastic cable on it. I can't imagine that I would ever have replaced a three core with a 2 core. The old black one had plaited cotton-covered rubber cable as I recall, but I still don't remember that one being earthed, either.

Arfa