These look like electronic ballasts for 250 watt lamps but the 4 amps is too high(?) and OCV is 600V?

http://www.ebay.com/itm/391121478552

If the ballast uses just plain doubler on the input (and not any power factor corrector; as most older PC's,...), the power factor would be around 0.5..0.6 and then the 4Arms is quite realistic for a 250W system.

Looks like electronic ballasts for 250W probe-start MH lamps.

Ok, but the real odd thing is in the last pic. It shows the back with a label "Photo Diode Light Status" which I've never seen before. How would these connections be used and what purpose would they serve?

These not looks like ballasts at all.

Venture is for some time offering a system varying real power to the lamps so, the light output remains constant over the lamp life. That means the lamps run at full power only close to the end of their life, so the power input for the given minimum illumination requirement is reduced by something around 15..20%.
So with an electronic ballast, the photodiode could serve the purpose of sensing the real lamp output, so the lamp power could be adjusted to get the same effect as the present Venture system (however Venture's system does not use any feedback, it either just counts the burning hours, or monitor the changes in the lamp electrical properties and "guess" the needed power correction in that way)

Interesting. Thanks Medved! Then these units must've been used in a sophisticated setup..and my mind is running around trying to figure out what sort of environment these 250 watters were used in. An industrial setup requiring good control or optimal lamp-run? Commercial setup for long life & low maintainance?..