I've never seen an MBU lamp operating in real life. I guess they are a very cool white temperature?Not really, not the same as MH at all for instance. The light is more blue/green than white. There is nothing in the lamp to produce any components of white light.I was lucky enough to receive the MB/U lamp I bidded for on e-bay a while back on Christmas Eve (thank you Claire for the original link!) and immediately went about fitting it in the still bowl-less GEC Z8430CM I purchased from Harrison Lighting. The new MB/U lamp compliments the existing MBF/U and retrofit SON lamps I have for this lantern.
The light the lamp produces is very harsh, cold and clinical nature. It's even, arguably, unpleasant to the eyes, to the point where they seem to sting! But the lamp's outer jacket is undamaged, so it should not be able to emit UV light.
The colour it produces reminds me of going into a shop with ancient fluorescent fittings where a tube only gets replaced when it fails. Over time, the shop ends up with a mixture of warm 'pink' ones, neutral white ones, and occasionally those hard-to-look-at cold 'blue' ones!
I thought it would be worth trying the GEC Z8430CM with the MB/U lamp next to an MBF/U lantern (in this case, a recently aquired early-version Phosco P111 from 'posh' Frinton-on-Sea in Essex) to see how they compare. This is the result...
Admittedly this isn't quite a fair comparison - the 250w MB/U easily overpowers the 80w MBF/U, so I placed a piece of card between the two so you can see more clearly the difference in colour on the wall behind. The familiar 'white' MBF/U colour is clear to see, but as the MB/U lamp is the dominant light source, your eyes eventually adapt to it and it becomes white. Thereafter, your eyes interpret the MBF/U lamp as pink!