Lamp life claims

Eurolux Day/Night lamp’s claim a life of 6000 hours on their packaging. It’s obviously not practical to record the exact number of hours that the lamps are on. But it would be generous to assume 12 hours per day. That equates to 500 days. How does one then keep a record of a lamps performance in order to hold Eurolux to their claim of a 6000 hour life? I tried writing the date of when a lamp Is fitted plus the anticipated end of “life” Activated 19th May’19. It should have lasted at least 16 months at a generous 12hours/day. It failed before today 11May’19. Unfortunately this is not enough for Builders Warehouse. They expect one to produce an invoice going back 500 days. Builders Warehouse have advised that in future I should record the till slip number on the lamp together with the date that the lamp was “activated”. The flaw with this is that the date of purchase may not coincide with the date that the lamp was fitted. But at least it’s a commitment from them to get Eurolux to honour their claim of a 6000 hour lamp life.