A break-even point with blanks left in

A replacement product’s operating efficiency does not establish when its additional manufacturing emissions will be repaid. This methods note constructs a conditional break-even model for a working desk light while leaving unsupported parameters explicitly unknown. The GHG Protocol Product Standard, European Commission energy-label guidance, and UK conversion-factor methodology inform the treatment of service equivalence, electricity boundaries, and comparison limits. A hypothetical contrast between two operating schedules illustrates sensitivity without assigning a real footprint. The analysis then considers changing electricity supply, remaining product life, later replacement, and unmatched service at the horizon. No numerical break-even date or saving is claimed. The practical outcome is a decision record that distinguishes useful conditional arithmetic from an environmental conclusion requiring product-specific evidence.