You can cut off 25mm or slightly less.say 21/23mm of say 10mm rod,place it inside the angle and weld it in.Or better still,make up a no of 45mm loa x10mm wide x 2 or 3mm thick steel flats,bevel each end ,each side 10 mm long 45 degrees to a point,and bend to a right angle,10 mm from each end,bevel the edges and weld them in.the dimensions are approx and it will take a few experiments to get it right but this is the "pro way"of doing it.Filling the gap with excessive weld is bad practice especially with MIG,if you are a good welder use arc approx 100 amps 3 runs 2.5 mm rods,cooling off between each run.Arc welding is better in my view for these light tubes but I know I am a lone voice here.And all edges should be bevelled 45 degrees back on the sides that are normally ground flush,too many of the welding in the photos is not and the edges have a wafer thin join. and while I am at it no more than 20 thous gap anywhere,this practice of filling in gaps with excessive welding is bad sloppy practice.David
