i have done it
i replaced the opalbulb with a led spot (app. 15 watt).
i dont know the lumen i dopnt know the ligtcolour but it works very well.
my spot had no diffusor so i used a milkwhite plexi-glass.
no brightness falloff to the borders.
with 4x5 i have enough light (10 sec for 13x18 cm)
but for 24x36 mm i have to expose the baper for 13x18 cm about 30 seconds.