Thanks Ria
Well I'll just have to trust the specs on the label then and hope it's keeping current between 0.8 and 0.85A
It is the cheapest way to drive a 90W and it's not like I'm running it for hours on end.

Correct current for a 90W is nearer 0.9A but 0.85 is close enough. Lamp voltage when fully run up should be 110-112V but remember that a SOX lamp's voltage will rise initially during warmup before dropping down to the normal running level.

By the way, to get the best lamp life, it's always best to run it for a few hours, and not to switch it more than once every 24 hours. I usually run mine for 4 or 5 hours, but I only use magnetic ballasts so it's easy to monitor voltage and current. The only time I tried an electronic ballast supposedly designed for SOX it under-ran it horribly.

Thanks again
But where does the 0.9A come from?
The official Philips specsheet says 0.82A

I just looked that up, and you're right, but the general rule has always been 0.6A for up to 55W and 0.9A for over 55W. The voltage specified seems a little different as well 

No you were right about the voltage, it's 112V for the 90W

I've made a combined PDF file of all the main pages of the whole SOX series.
Perhaps comes in handy for quick reference.
You can get it here: Click

Thanks, that will be useful. I had some of the Philips data sheets, but not all of them 

Sorry, removed the link because there was 1 page in Dutch (psg 35W)
I'll rectify it and post again in 5 minutes.