High bay lighting is the kind found in factories and showrooms, typically used in high roof spaces to create wide area task or display based lighting levels.
Much has been written about high bay lighting on the 'net. Here's a quick note that deals with cost compared to Tungsten fittings.
Consider a 250W High Bay fitting, This will generate 15 lumens per watt. Note that the light quality is pleasant to the human eye and therefore this practical value is closer to 19 (pupil lumens).
A 4000K CFL will generate 90(145) lumens/watt pupil lumens/watt, note that the 5000K units have better efficiency but give that 'crisp' white light that is found in hospitals etc. Actually the 5000K (104/190) can suit some types of showrooms (e.g. Cars more than Clothes).
The running cost for a 10 hour run at 14.7p Kw/h is:
Tungsten : 36.75p
CFL 4000K : 4.82p
CFL 5000K: 3.68p
For 10 fittings running 10hours for 310 days per year the costs are:
Tungsten : £1139.25
CFL 4000K : £149
CFL 5000K: £114
CFL fittings are more expensive than simple tungsten fittings, and really need to be the HF (High Frequency) type to be comfortable on the eye. In the high-bat commercial fittings, 1-10V dimming is a common cost option. A typical 38W or 2x26W fitting will cost £100-150. This gives a straight line payback period of just over a year (actually about 18months if you assumed that you borrowed the money to buy the fittings at 5% interest).
A point of care here, CFL lamps are available in a range of colour renditions for the same power, if you mix these in the same area they will be visually discordant. As a very rough guide:
3500K (and below) -- Good for domestic use, creates a warm feel
4100K -- Shop and showroom lighting with a warmer feel
5000-5500K -- Shop and showroom lighting with a crisp feel and good colour rendition (most economical)