In terms of Tungsten light - I can visualize 50watts - how much light output that relates to. So how much light output will a 880w flourecnt Keno Flo type fixture output in equivalent to Tungsten bulbs?

I need a good soft Key light for our production company. Ive never used Keno Flo's or Flurecents but i like the idea of less Heat output. I need it to be as soft as possible- cover a large area - powerful - a lot of light output - with a dimmer. It needs to be convenient to put in a case and travel on locations. This would be our main Key Light. Looking at websites i am overwhelmed by all the choices. So many sizes and shapes.

100watts of Flourecent = 500watts of tungsten. Is this correct ratio?

Just multiply the fluorescent figure by 4 not 5. Although some manufacturers unscrupulously list the equivalent wattage out front and the real wattage in fine print. You should verify which wattage they are quoting on the 880 one. Its probably 16 55 watt lamps which would give 880w draw and multiplying by four would give around 3520w equivalent.

Another way to look at it is this: each 55w bulb puts out on average about 3000 lumens depending upon bulb quality and ballast power factor, so if there are 16 of them that's 48000 lumens. At between 10 to 20 lumens per watt (for tungsten) that would be between a 2400w and 4800w instrument equivalent, so the 3520 figure falls in between the two at around 15 lumens per watt.