About the history:

I am showing some text from a specialist book and a PHILIPS-catalog on an MV medium-pressure lamp with an isothermal bulb shape and phosphor.

Andy Oakley owns such a lamp. My wish is to see this photo here, too.



Source: PHILIPS-catalogue Australia, 50s


Source: ELECTRIC DISCHARGE LAMPS, by H. COTTON, LONDON 1946, CHAPMAN & HALL LTD.


Source: ELECTRIC DISCHARGE LAMPS, by H. COTTON, LONDON 1946, CHAPMAN & HALL LTD.


Source: ELECTRIC DISCHARGE LAMPS, by H. COTTON, LONDON 1946, CHAPMAN & HALL LTD.


Source: ELECTRIC DISCHARGE LAMPS, by H. COTTON, LONDON 1946, CHAPMAN & HALL LTD.


Source: ELECTRIC DISCHARGE LAMPS, by H. COTTON, LONDON 1946, CHAPMAN & HALL LTD.


I suspect this type was one of the first mv lamps with a phosphor.


Regards

Olav

Ah yes, the MAF/V. This is easily one of the rarest mercury lamps out there, even James Hooker doesn’t have one and his example on lamptech was borrowed from a museum. I think Andy is the only member here lucky enough to own one of these incredible lamps.




https://www.lighting-gallery.net/gallery/displayimage.php?album=6641&pos=25&pid=114881

Just when we thought our bucket list was nearing completion, along comes this gem

Thanks for uploading these extracts from documents regarding the MAF/V lamp Olav.
It is a fascinating old lamp and I believe the earliest type of mercury lamp to have a phosphor coating.
Several manufacturers produced this lamp from what I can tell although I did not know Philips made it until I first saw your 1950s Philips catalogue.
It was the kind of lucky find that is unlikely to be repeated.

As it is one of my most precious lamps, it is packed away very safely and I have not seen or lit it for a couple of years now.
I must try and take a couple of improved photos of it when I get the chance. Due to the shape and size of it, taking a good photo is a bit tricky.
Here is one of the photos I took a few years ago.

A small supplement of technical data.
The cutout is from the G.E.C. Catalog from 1951:


Source: G.E.C. Streetlighting Equipment catalog, London1951, page 85

I found a small addition to the lamp MAF/V 400W:


Source:
E.L.M.A.  ELECTRIC LAMPS, 1949, page 84 and 85,
Spottiswoode, Ballantyne Co. Ltd. London and Colchester

One of the few items on our bucket list that we still have to find. Maybe one day  

Has an erratum never been corrected?

At the meeting with Andy in Northampton, there were many good and interesting discussions about lamps.

It was a great pleasure for me to see the OSRAM GEC MAF/V 400 W (isothermal outer bulb, medium-pressure) and OSRAM GEC MBF/U 400 W (cylindrical outer bulb, high pressure) lamps light up.

Andy later made a very interesting comment that I want to address here.

In the book "ELECTRIC DISCHARGE LAMPS, by H. COTTON, LONDON 1946, CHAPMAN & HALL LTD." printed in 1946 and in the book "Electric Lamps", issued by the lighting service bueau, ELMA, London, first printed in 1949, a graphic is made with information on the temperature at the outer bulb.

Apparently, an error was copied over and over again over the years without being noticed.
The fact is that the temperature is highest in the inner center (the arc tube) of a discharge lamp and decreases towards the outside.
However, the graph shows exactly the opposite.


Source: ELECTRIC DISCHARGE LAMPS, by H. COTTON, LONDON 1946, CHAPMAN & HALL LTD.

To emphasize this, I have left the original temperature information in black type and inserted the corrected temperature information in red type.

I would be interested in your views and opinions on this.

Oops    

This is an interesting consideration, but I do think the original may be more correct.  It would not be logical at the lower end that the temperature increases when moving further downwards, and closer towards the relatively cold lower end of the arc tube. 

The primary heating mechanism of the glass of such lamps is absorption of radiation.  The absorbed photons are decelerated and increase the phonon energy in the glass (ie heat).  We can see this, because even the outerbulbs of vacuum lamps like HPS and certain metal halide types become intensely heated during operation even though there is no gasfilling for conducted or convected heat loss.  Glass is quite transparent to visible light and shortwave IR-A, but a strong absorber/reflector of longer wavelength IR-C as radiated by the hot arc tube. 

However, due to the gasfill of low pressure air/nitrogen in this lamp, I would expect the cap area to become rather hotter than the minimum temperature indicated in this drawing.  Beyond the lower temperature of 100C labelled at the shoulder of the bulb, I would expect temperatures to rise again towards the neck.  Perhaps I should bring a thermal imaging camera or snake-eye type thermometer next time when visiting Andy to learn more about the energy balance in these fascinating old lamps!

Thank you James for your very interesting explanation. It would be very nice, if it were possible to use a thermal imaging camera. 
I've learned something new, for that I thank you.

I have often thought about buying a thermal imaging camera, but the good ones do not come cheap. One day, maybe