Why the number is a projection rather than an observation
Nobody runs a test for the full duration a figure implies. Samples are operated under controlled conditions for a defined test period, output is measured at intervals, and the resulting curve is extrapolated forward using a standardized projection method. The published figure is the output of that model.
That matters for how you read it. The number carries the conditions it was produced under: a specific drive current, a specific case or ambient temperature, a specific mounting arrangement. Change any of those in the field and the projection no longer describes your installation. Where a product page publishes a lumen maintenance or L70 value, quote it from that page and treat it as the manufacturer's test result under stated conditions (verify the figure and its conditions on the page, and do not present it as a guarantee of service life).
What shortens the curve in a real installation
Heat leads the list. LEDs do produce heat, and the junction temperature inside the package is the single strongest driver of how quickly output declines. A strip sandwiched into a sealed cove with no path for heat to leave sits at a higher junction temperature than the same strip on an aluminum channel with air behind it, and it will not follow the same curve.
Drive current is second. Running a package harder gets more light per foot and more heat with it, which is one reason a high output series and a low output series are not directly comparable on this metric.
Environment covers the rest. Moisture reaching an unsealed run, dust settling on a diffuser, and ambient temperatures near the top of a product's stated range all take their share. A dirty lens can cost more delivered light than years of gradual decline, and it is the one factor you can reverse with a cloth.
Then there is the part the tape has no control over. A run is only as available as the driver feeding it, and a driver operating hot or near its capacity is often what needs attention first in practice. Size it as watts per foot times installed length plus at least 20 percent current headroom, confirm that guidance before ordering, and give it a serviceable position with air around it.
Using the figure when you specify
Compare like against like. Two lumen maintenance figures are only comparable if both were produced at similar drive currents and similar temperatures, so read the conditions alongside the number rather than the number alone.
Then design so the assumptions survive contact with the building. Mount higher output runs in an aluminum channel, since it helps dissipate heat and protects the tape, and specify honestly rather than optimistically. Where output density is the priority, one suitable option is the LEDClub 24V SMD 400 Series, checked against its published lumens per foot, watts per foot, and maximum run length before it goes on a schedule. The wider strip lighting range lets you weigh output against the heat it brings with it. Long runs raise a separate question about delivered output at the far end, which our article on voltage drop across LED strip runs sets out with the wire gauge calculation.
