I bought some Total BV 75W80 today

[myglaren]

uPVC doors & windows, conservatories, composite doors etc.
Manufacture only, no fitting.

[charentejohn]

My personal view is always PPM Planned Preventative Maintenance. Most obvious one (semi retired electrician) was replacement of fluorescent tubes in factories. They may look ok but lose 50% of their output at half their lifespan, also chasing intermittent failures if you do nothing is costly. So if a tube lasts 2 years before losing output (4 years to failure) you change all of them on a rotating basis (with starters) every 2 years regardless of what they look like. Just a specific example but applies to all mechanical things.

The same approach to cars is also true, engine oil change is the obvious example. It has a fixed duration based on workload so you know when to change, the opposite would be when it rattles and clanks rebuild it.
So always best to replace a part, or lubricant, before it fails than after it has, as it may take something else with it. Reckon I will buy another 2L and do the next change in a couple of years anyway, why not.

[myglaren]

My personal view is always PPM Planned Preventative Maintenance. Most obvious one (semi retired electrician) was replacement of fluorescent tubes in factories. They may look ok but lose 50% of their output at half their lifespan, also chasing intermittent failures if you do nothing is costly. So if a tube lasts 2 years before losing output (4 years to failure) you change all of them on a rotating basis (with starters) every 2 years regardless of what they look like. Just a specific example but applies to all mechanical things.

Just common sense.
Three of our factories have >70% of the fluorescent tubes burned out and the rest are at approx 1cp.
The one I am in mostly has 16 mercury vapour lamps, 9 of which are dead (one caught fire a few months ago and killed half the electrics in the factory).
One guy went up a high set of moving stairs to put the fire out, the extinguisher dispensed a cupful of powder and died.
It was replaced last Wednesday

The electrician was supposed to come back and replace all the dead bulbs (each one in a critical area, the ones that work don't really matter) but I presume he quoted a price that management were unhappy with.

I replaced a couple of hundred tubes five years ago - nothing has been done with them since then. We have to hire a traveling platform to access them as our cherry picker was buggered so swapped for services when they wanted some vacforming machines shifting.