Hi there.

I am very curious about the wattage ratio of common mercury blended lamps. So i assume they are always 50/50? Like

Philips ML 100W with 50W mercury discarge and 50W of the tungsten coil
160W with 80W mercury burner
250W with 125W mercury burner and
500W with 250W mercury burner?

I found absolutely no interesting info on the internet, and I hope as well that this is not already part of an existing thread here in the forum.

All the best... Marc

Larger portion of the power goes to the incandescent, my guess would be around 60% on incandescent and 40% the discharge. The reason is arc stability...

Don't forget even when the arc has around 120V drop on a 230V lamp what may seem as half, the voltage and current shapes and the consequent power factors of the components make the power to go almost 60% for the incandescent for such lamp.
What is deceiving is the rather low light output of the filament part (compare to an incandescent of the same wattage), it operates at rather low temperature. There are two reasons behind: Life time (mainly for the start cycles, when during warmup the incandescent part sees nearly full mains voltage, while for steady operation it has barely 150V on it), plus the rather low fill pressure of the outer where the filament is (compare to the incandescents; needed to avoid excessive thermal losses on the discharge tube, so to allow its correct operation). That means the filament evaporates quicker and that has to be compensated by the use of lower operating temperature. Plus a factor is, the gas fill has to contain more of the Nitrogen to prevent arcing (because of the lower pressure), which means higher thermal losses from the filament.

Thanks Medved for your description!

This means that the dimensions of those blended lamp arctubes are of littler smaller dimensions than their equivalents 50/80/125/250W, or did they may be used the same arctubes, just slightly underdriven?

Marc, the best answer to your question is: it depends on the lamp. First of all, SBMV lamps are not made with standard HPM burners, but with dedicated ones burning at lower voltage to account for the discharge's re-ignition peaks (i.e. to prevent a too easy extinction of the lamp in fluctuating mains). Below are the characteristics of the mercury burners employed in European-specked lamps:

100 W: 30 W (86 V, 0.47 A)
160 W: 51 W (90 V, 0.75 A)
250 W: 78 W (88 V, 1.2 A)
500 W: 214 W (120 V, 2.4 A)

As for the dimensioning of these burners, like their standard counterparts they are optimized for maximum efficacy (i.e. max discharge power load) with a wall load between 7 and 11 W/cm² (to ensure a sufficiently long life).

Now you see from the data above that the filament/burner wattage ratio ranges from 70/30 to 57/43 with an average around 66/34. The reasons for such a ratio are first considerations related to the filament operation, and second the production of white light with enough red content (around 12 %) while still obtaining a long service life (around 10 kh at 50 % failure). Interestingly, the first modern SBMV lamps did not have a phosphor for the production of red light and as a consequence the power ratio was typically 72/28 which corresponds to an equal amount of light emitted by the filament and by the mercury discharge.

Resurrecting this topic as I have a question that I believe to be related.

How critical of mains voltage are SBMV lamps..? I have just acquired some 160W lamps rated at 220-230V. However, my supply voltage is quite a bit higher, it averages around 245V as we are literally across the street from a substation. I know that the legal tolerance of supply here in the UK is 230V -6%/+10% which gives a range of approximately 216V to 253V, so we are well within that, but what is the tolerance of the lamp..? Will the life be reduced by running on 245V and if so by how much..?

Resurrecting this topic as I have a question that I believe to be related.

How critical of mains voltage are SBMV lamps..? I have just acquired some 160W lamps rated at 220-230V. However, my supply voltage is quite a bit higher, it averages around 245V as we are literally across the street from a substation. I know that the legal tolerance of supply here in the UK is 230V -6%/+10% which gives a range of approximately 216V to 253V, so we are well within that, but what is the tolerance of the lamp..? Will the life be reduced by running on 245V and if so by how much..?

It will be reduced, mainly the filament part. In your case it means about 8% overvoltage at startup (assume about 40V drop across the cold lamp), so according to the incandescent performance chart it means about 50..60% life (assume normal filament evaporation is the only dominant mechanism). But if it would be operated at long cycles (ON time longer than the 10 hours/start the rating is designed for), it may compensate a bit (shorter time spent in the low arctube temperature region where most of the evaporation is happening).

At time the SBMV's were made with different voltage ratings, usually the formal rating sets were either "220V" (115..125V), "230V" (225..235V), "215V" (235..245V) or later to two members "220..230" and "230..240V". For you would be then suitable the "240V" or "230..240V" type...

Thanks for the reply, I was sure you'd know 

It will be reduced, mainly the filament part. In your case it means about 8% overvoltage at startup (assume about 40V drop across the cold lamp), so according to the incandescent performance chart it means about 50..60% life (assume normal filament evaporation is the only dominant mechanism). But if it would be operated at long cycles (ON time longer than the 10 hours/start the rating is designed for), it may compensate a bit (shorter time spent in the low arctube temperature region where most of the evaporation is happening).

At time the SBMV's were made with different voltage ratings, usually the formal rating sets were either "220V" (115..125V), "230V" (225..235V), "215V" (235..245V) or later to two members "220..230" and "230..240V". For you would be then suitable the "240V" or "230..240V" type...

Osram did also offer their HWL as 1000W version!