LED lifespan, L70 and lumen maintenance

At a glance

Definitions are from IEC 62722-2-1:2023 (clauses 3.2 and 3.3), the NREL/DOE guide (2010) and SI 2021/1095 Sch 3. A declared life is the maker’s claim, not a guarantee.

What L70, B10 and B50 mean

An LED does not usually fail like a filament lamp. It fades. ‘L70’ is the number of hours until the light output has fallen to 70 per cent of its initial value; the NREL and US Department of Energy guide to evaluating LED lumen maintenance describes it as the expected operating hours until output has diminished to 70 per cent of initial levels. Seventy per cent is a convention for the point at which the loss becomes worth acting on.

The ‘B’ figure says how many units in a batch have got there. The international luminaire performance standard IEC 62722-2-1:2023 defines useful life, written LxBy, as the length of time until at most a percentage y of a population of operating LED luminaires of the same type have degraded to the initial luminous flux multiplied by the luminous flux maintenance factor x (clause 3.3). So L70B50 is the time by which half the units have fallen to 70 per cent, and L70B10 the time by which no more than one in ten has. The drawing shows three units fading at different rates; the curves are an assumption for illustration, not data from any product.

Two consequences matter to a specifier. A B50 life is the middle of the spread, so half the units of a type reach 70 per cent sooner. And a life figure describes light loss, not the whole product: the IEC note says useful life includes only operating luminaires, and that it does not account for whether a luminaire can be replaced.

What a life figure does not tell you

It is a claim to be checked, not a guarantee. The IEC standard states that the lifetime of LED luminaires is generally much longer than any practical test, that verifying a maker’s lifetime claim is outside its scope, and that its categories are based on lumen maintenance over a finite test time; the category number does not imply a prediction of achievable life (clause 1). A declared life of 50,000 hours is therefore the maker’s figure, and the useful questions are what it is based on and under which conditions.

Temperature is part of the claim. The standard defines a rated ambient performance temperature, the highest room temperature at which the rated performance applies, declared by the maker; it notes there can be more than one, depending on the lifetime claim (clause 3.2). A fitting with a closed shade, a ceiling void or a hot cabinet may run hotter than the condition the figure was declared for. Ask what temperature the figure assumes, and what the temperature is inside this fitting.

The source is not the whole fitting. The life of an LED source says nothing about the driver, the dimmer pairing or the joints. The IEC definition leaves out units that have stopped working, so outright failures are a different risk and need their own question: what is the driver’s declared life, and is it a separate, replaceable part? Our sheet on LED drivers for decorative luminaires covers where drivers sit and how they are reached.

Decorative fittings may not carry test data. The IEC scope says that for some types of luminaire, for example decorative or household, the provision of performance data under that standard is not appropriate. Do not assume a chandelier has a test report; ask what the partner workshop holds for the module and for the fitting.

What UK law adds. The Lighting Products Regulations 2021 (Schedule 3, paragraph 6(2)(e)) require the L70B50 lifetime in hours on the packaging of an LED or OLED light source, and Table 5 requires the lumen maintenance after endurance testing to reach a minimum calculated from that declared lifetime, capped at 96.0 per cent, with the source surviving the test. Our UK Ecodesign rules sheet sets out the scope; these rules concern light sources placed on the market, not a promise about a chandelier in a hotel.

From rated hours to years of service

Rated hours are not years until you say how long the lights are on. The drawing is plain arithmetic: rated hours divided by hours used per day, divided by 365. At 16 hours a day a 50,000-hour figure is 8.6 years; at 24 hours a day it is 5.7 years. For 35,000 hours the same two cases give 6.0 and 4.0 years. These are the years until the rated figure is reached by a typical unit, not a promised service life, and a B10 figure would be reached earlier.

The table gives the shape of use in a hotel or restaurant in words only. We found no published operating-hours data for hospitality areas, so this is general practice and your operator should replace it with the real pattern.

Planning spares and replacement

There is no honest industry percentage for spares: it depends on the product, the hours and the operator. We give a method, and every value stays for the partner workshop and the operator to supply.

1. Count by type. List each module and driver reference and how many are in service, from the lighting schedule.
2. Ask for the failure basis. Request the declared life with its temperature and drive current, the test basis, and any return or failure experience for this module and driver from the partner workshop’s supplier.
3. Keep drivers apart from modules. They age differently and are usually changed separately.
4. Hold spares from the same batch. A replacement from a later batch can differ in colour; our colour temperature sheet explains tolerance and bins. Ask for a colour-matched batch and its date code.
5. Ask about continuity. What happens when the module is discontinued: is there a last-time purchase, a replacement that fits, or a re-lamp of the whole fitting?
6. Set review points. Review each fitting against its declared life at a chosen hours run, and replace as a group where uniform colour matters more than saving a few modules.

The record below is a starting template for the handover pack. It sits with the maintenance information described in our sheets on O&M information for decorative lighting and spares and replacement cycles.

For each fitting tag the maker is to declare the LED module and driver references, the declared lumen maintenance life as L[70]B[50] in hours [ ] (and L[70]B[10] [ ] where requested) with the rated ambient performance temperature [ ] degrees Celsius and drive current [ ] mA it applies to, the test basis (module test report and projection method, or luminaire test) [reference], and the lowest and highest dimming levels the figure covers. The figure is a declaration, not a guarantee, and is to be repeated in the care and maintenance sheet.

LED modules [and drivers] are to be replaceable on site without damaging glass, metalwork or finish, by [a competent electrician / maintenance team], through [the access shown on the shop drawing]. The maker is to state the replacement procedure and the isolation point, and to confirm the module and driver can be purchased for at least [ ] years after handover or name the replacement route.

Spares of [modules] [quantity] and [drivers] [quantity] from the same colour batch [date code] are to be supplied with [the delivery] and listed in the handover pack with location, references and declared life. The operator is to record hours run and the date of each replacement against the fitting tag.

Standards and sources

• IEC 62722-2-1:2023 Edition 2.0, Luminaire performance, LED luminaires: scope and clause 3 read in a preview, 7 Nov 2026; confirm the edition.
• SI 2021/1095 Lighting Products Regulations 2021, Sch 3: para 6(2)(e), Table 5; read 7 Nov 2026.
• NREL/DOE, Guide to Evaluating LED Lumen Maintenance (2010): L70 definition; outdoor products; dated.
• BS EN 62717:2017+A2:2019, LED modules for general lighting: Current per listings; not read.
• IES LM-80 and IES TM-21: named only; neither read; confirm editions.

Questions we are asked

What does L70 mean on a data sheet?

It is the number of hours until the light output has fallen to 70 per cent of the initial value. Ask which temperature and drive current the figure was declared for, and whether it was measured or projected.

What is the difference between B10 and B50?

B50 means half of a population of units has reached the L70 point by that time; B10 means no more than one in ten has. B10 is therefore the earlier, more cautious figure, and a better basis for planning replacement where uniform colour and brightness matter.

Is a 50,000 hour rating a guarantee of ten years?

No. Hours are not years, and a rating is a declared figure, not a warranty. At 16 hours a day, 50,000 hours is about 8.6 years of use; at 24 hours a day about 5.7. Half of the units in a type reach their L70 point sooner than the B50 time.

Does the LED rating include the driver?

Not necessarily. The IEC definition counts operating luminaires only, so outright failures of a driver or joint are outside it. Ask for the driver’s declared life and whether it can be replaced separately.

How many spare modules should I order?

There is no reliable general percentage. Ask the partner workshop for the failure experience and continuity of the module and driver, hold spares from the same colour batch, and agree the count with the operator against the hours run.

Do I need to replace all modules in a room at once?

Not for safety, but light output and colour drift over time, so mixing new and old modules can show. Where uniform colour matters, replace in groups and keep a colour-matched batch.