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When tritium started to get used on oyster case professional models, the designers obviously wanted as much visible tritium on the hands as possible so in R&D the original hour hands didn't have the lattice work, just the lum.
The difference being that these modern day professional models weren't dress watches any more, for the first time ever, people were going diving and and mountaineering and such whilst wearing their watches, the original tritium didn't get make it through testing so the hand was latticed.
The non professional models weren't really seeing much deep sea diving so the hands on the date just etc. did not require as much lum and therefore did not require any structural support.
Antidotes-
Interesting thanks @Antidotes and @Stonehedge .
Had to get the bus/train/bus to collect a bike box, and on the way back swung by my mate at work. Popped the old crystal+cyclops out the Stendardo and replaced with a 2,5mm mineral by Sternkreuz. Looks so much nicer now though it's still a low end watch by this thread's standards.
Anyway, it's a 0S10 Miyota inside, the allwatchparts site says those hands are 120/70/17(26) .
Not sure I want to lose the sky-blue chrono, but keen to replace the hour and minute hands with modern lume. However, money, so what are my options away from Merc cathedrals? I see a few baton style hands on ebay but risk the lume being old and inefficient.
pdlouche
Cathedral hands date back to the very early 1900s
In fact, Rolex seem to have used them before lume was a thing.