Triple spotlight: bulbs blowing in one of the fittings

One of the telescopes at the Institute of Astronomy still uses 200V. Apparently the electricity company turned up to change everything to

240V and decided to "back away carefully".

I don't know where they get the power from (probably a transformer).

Reply to
Martin Bonner
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The thing Harry is missing is that continental light bulbs won't be

230V; they will be be 220V. It wasn't that the evil continentals forced us to use their sub-standard voltage. Everybody kept using the same voltage and manufacturers had to support them - except that doesn't work for incandescent light bulbs and the EU didn't try to legislate away the laws of physics.
Reply to
Martin Bonner

at the ADC theatre at the time there was an autotransformer tureneing the

200v into 240 so that the lighting control board could work properly. The loss in the control circuits meant that the output was back to 200v. This meant we could borrow kit from the Arts Theatre without lamp changes. ;-)
Reply to
charles

They do that all the time!

Reply to
The Natural Philosopher

En el artículo , Martin Bonner escribió:

I could believe that. Some telescopes seem to run on string, sealing wax and a prayer.

Today, though, most kit with switching power supplies will run on pretty much from 90v - 300v.

Reply to
Mike Tomlinson

Martin Bonner has brought this to us :

I was aware of that, but the lamps I have come across are marked 230v. I'm guessing some importers /sellers are just not aware, or don't care that the EU rated lamps don't survive very long on 240v.

Reply to
Harry Bloomfield

I rather doubt that. There's a very tight relationship between voltage rating versus efficacy and service life with tungsten filament incandescent lamps. It only needs a small percentage departure from the "Design Voltage" to greatly alter the efficacy and lamp life, the latter of which is quite tightly specified which is the main reason for such lamps being specified more precisely for the voltage used in the regions they are sold in.

I suspect a European lamp wouldn't even last as long as the 750 hours rating standard of the USA on our 240v mains supplies. The Yanks decided to sacrifice some lamp life for improved efficacy, notwithstanding that their lower 117/120v filaments provide an improvement in efficacy over our 240v filament lamps without having to resort to such a sacrifice in the first place.

Be thankful that, whenever you see a modern LED lamp being equated to a

60W incandescent, it's the American 60W lamp that's used as the reference rather than our less efficacious 240v variety. :-)
Reply to
Johnny B Good

Johnny B Good presented the following explanation :

I'm not sure I understood what you were trying to explain, but a

117/120v lamp's life on 240v would be measured in minutes. The last time I was annoyed by lamp voltage ratings, they were a set of oven lamps marked 220/240v, an ebay purchase. Our oven take four, so I replaced all four as two had expired. They survived just one week of intermitant use in the oven, a matter of hours. That was many months ago and they were then replaced with the correct 240v items which have survived fine ever since then.

In my youth, with an interest in photography, such lamps were over run to produce more light for the actual photos, but their life was short. During setting up a shot, it was normal to run them on a reduced voltage. The usual dodge was to have a series / parallel switching arrangement, to run two lamps in series.

Reply to
Harry Bloomfield

More like milliseconds! I was referring to the use of 117 or 120v lamps

*in America*, not their use on 240v mains voltage.

Even when under-run, the higher voltage will shorten their service life but I'm surprised at the extremely truncated life you experienced. With oven lamps (and probably fridge/freezer lamps as well), the main consideration isn't so much their luminous efficacy as their operational life, particularly so when such lamps may have to cope with an environmental temperature that typically ranges from 180 to 220 deg C.

Photo-floods were typically rated for a mere ten to fifty hours at their 'working' voltage. It was common practice to use a dropper resistor to both reduce running voltage so as not to 'burn up' their full voltage rated life during the initial light balancing setting up phase but also to take the 'sting' out of the initial switch on surge.

The current surge when switching to full voltage was a much smaller 'insult' to the filaments when the setup was deemed ready for actual photography. You might only burn photo-floods at their full voltage for

10 or 15 minutes per one hour's photo shoot in a studio.

Indicator and panel illumination lamps are designed for even longer lives (10,000 hours or more) since efficacy isn't the primary concern. Indeed, incandescent filament displays, such as those used on the first electronic fuel pumps at filling stations had lifetime ratings of 50 to

100 thousand hours.
Reply to
Johnny B Good

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