out of interest ,this is the reply i had from the horses mouth, kaisers anyway.
it would be pretty helpful if thet put info like this on their advertising, it wouldnt be as glamorous or glitzy but would at least be honest.

quote..'The light distribution depends also on the quality of the opal lamp
itself. There are small differences in the inner coating of that bulb.
That can cause sometimes an uneven light distribution. Some very critical
users are testing bulbs of different manufacturer runs.

A better light distribution is given by a halogen construction. The
mulitgrade head and the color head contains that construction. It will
give a smoother light and a better distribution.
The disadvantage is a reduced brightness because of the integrated
diffusor plate.
I know, that is not the solution for your customer, but a head with an
opal bulb can never
give an absolutly even light distribution.' end quote.

thankyou for all your replies, i have learnt alot from this .