Hi all,
recently i got some used 400W MH fixtures equiped with lamps (Disano Indio art. 1158, 25€ each).
However, i wonder why there are 2 current options for 400W versions (3.4A and 4.2A, i got 3.4A).
Does anyone have any clue and/or bulb replacement suggestions? (i bought theese because i need a lot of daylight light in a reasonably cheap way)
Thanks!

Here is a photo of a similar product (same code, different lamp option):

Some MH lamps are designed for 400 MV ballast and some are designed for 400 HPS ballast and some can work on both.

Historically, high power metal halide lamps were made to be compatible to mercury ballast impedance. Hence, 3.25-3.4A rating. About 1980's European manufacturers started to migrate their lamp to HPS ballast impedance, running at slightly higher current and sometimes slightly lower voltage. A huge confusion follows. Americans seems never to follow this move.

Some lamps have dual rating, but generally prefer one of them. Philips HPI-T is said to prefer mercury ballast, while Osram HQI-T /D prefer HPS. BLVs are mostly HPS only.GE/Tungrsram made different quartz and ceramic lamps for specific ballast impedance use. Asian market is flooded with some unbranded MH lamps, with no datasheets you can only to guess. Generally, 2-electrode lamps may be HPS compatible, but 3-electrode probe start ones almost always expect mercury impedance.

Ok, thank you!

The HPI-T for example works on 3.4A only while the more modern HPI-T PLUS is made for both, HPS and MV (4.0A and 3.4A) ballasts.

In the 90s Osram stated for their HQI-T and BT range both options HPS or MV. Later they seem to stick to HPS gear.