The leak transformer is best simulated as high impedance constant current source. So the the voltage gradient when loaded is very high.

I don't think it would lower the necessary OCV, it would "only" make the starting more reliable (if the auxiliary probe got shorted to the main one by e.g. a mercury droplet, the other side would still ignite the lamp), but this is more related to pure mercury, as there the mercury dose really forms conductive droplets. In MH the nongaseous fill uses to reside in the form of solid salts, which when cold and solid state are not conductive, so do not prevent the starting probe from doing its job.

The OCV limitation of MH comes mainly from the ability of the cold electrode discharge to carry sufficient current to sustain the arc and to warm up the electrodes, which won't change with two starting probe design. And to allow the gap from the auxiliary probe to spark over, where the existence of two probes won't help either.


On the contrary, having the starting probes on both ends would create reliability problems, increase the risk of one side to be flooded by the condensing salts when cooling down. Then after restrike, as the thing is warming up, the just melting salts tend to be extremely aggressive towards anything metal when there is an electrical potential difference involved, so attack the leads when the salts are just starting to melt while the bimetal is not yet ON (could happen some seconds after ignition). When starting probe is just on one end, you can more easily design the lamp with fewer position restrictions yet still completely avoiding this problem (position ratings like e.g. "all burning positions except BaseDown" and having the starting probe at the base end, so the condensing salts will never flow towards the end with the starting probe...).

As I understand it also, the 500 watt MBTF lamps made by Thorn had a starting problem that was actually identified by Philips!, (or it could have been the other way round?), don’t quite remember now?, anywho,
The Thorn lamp only had one starting probe that could get shorted out by a blob of mercury dropping between it and the main electrode, stopping the lamp from starting, and from this Philips add two starting electrodes to stop this happening?

Upon going through the survivors in Warwickshire on mikes website, I only recognise 2 or 3 locations from your photos, and Mike's photos oc these lantens are older than your photos.

Since Friday gets pass Yes.

As for real measured parameters, I tried ML160 from GE and HWL260 from Osram.

GE ML160 230-240V

line voltage at that time: 225.6V
current: 0.708A
power 156.7W
power factor 0.98
CCT 3196
CRI 67
made in Turkey, which is unusual

Osram HWL250 235V


line voltage at that time: 224V
current: 1.081A (power monitor) 1.076A (RMS multimeter)
power:232.5W
power factor: 0.95
CRI: 55
CCT: 3512

date code f668 made in P.R.C.

Interesting, 160W GE lamp has significantly higher filament light to the burner ratio compared to 250W Osram. I have no more ML lamps to compare another. Both lamps notably run below their powers specs, likely because my line voltage at test time was below design voltage for both lamps. 

Another interesting fact is color temperature measured for 160W lamp just turned on is 2881K which certainly means the filament is overdriven compared to usual 2700K of plain filament lamp, though a little light from the burner may offset CCT at that time a bit, too.

Interesting document really!

Yes, it shows that at least Thorn mixed lamps are designed with with mains to burner voltage (power) ratio of 2.44:1 (220-230V 160W) and 2.4:1 (220-230V 250W). Does it still qualify as "approximately 2:1", you decide

There is still some uncertainty, as this book mentions two burner voltage ranges for 220 and 240V ML lamps, but only single mechanical specification for each burner wattage.

An interesting fact is that 160W and 250W ML burners are notably different mechanically to their plain mercury counterparts from 80W and 125W lamps. While 500W ML in fact re-uses the exact mercury 250W burner.  I believe the explanation is the difference in fill pressure, giving the burners significantly different cooling modes. While 80 and 125W mercury lamps are filled to 20-40 Torr of nitrogen, mixed light lamps are specified as >500 torr. This pressure difference is generally absent in 250W mercury vs 500W ML lamps.

In fact, two counteracting factors work in mixed lamps when compared to plain mercury one. Filament sure gives some significant extra heat to the burner, radiant and convection, but at the same time, higher fill pressure significantly increases heat transfer from the burner to outer bulb.

I am skipping 100W ML as a weird type, rarely seen in the wild.

Quick question then Dez, how come a 90w SOX is safe to run on a 140w SO/H leak transformer, when the 140w lamp is rated at a much higher voltage? Is the leak transformer able to self-regulate for the 90w lamp and it's lower running voltage?

Weren't you supposed to take a short break from the site, Eleco_SR304? 

Yes, sometimes Mike gets tips from people, but him photographing a lantern for his website is fine, the lantern isn't yours, there isn't a limit of one person to photograph a lantern. Also, he has credits on photos that someone else found. It seems like many of your finds are already known to other locals, and using this logic, you are doing the same as what Mike is being accused of...