Example for the dertermination of the maintenance factor due to technical data of LED luminaires and the specification of the room

To determine the maintenance factor MF and initial illuminance Ei (index "i" for "initial"), the intended use of the room as well as further basic parameters are considered:


Very clean non-smoking group office

Light source:

LED, rated service life: L85 = 50,000h (see chapter , Service life of LED luminaires)

Type of luminaire:

Closed luminaire, diffuser luminaire (e. g. Belviso D···)

Maintained illuminance Ēm in the visual task area:

500 lx

Annual duration of room use:

2,750 h/a

Period of operation with light management (see below): 

1,250 h/a

Maintenance interval:

3 years

Period of use:

20 years


The partial maintenance factors add up to:

Lamp maintenance factor LaMF = 0,93

Reasons: The lamp maintenance factor for LED can be equated with their lamp lumen decrease within their rated service life since the total failure is improbable to a negligible extent. For LED luminaires it can also be assumed that switching-off and dimming of the lighting due to presence detection as a reduction of the effective operating duration has a diminishing effect on the decrease in luminous flux of the light source.

The resulting LaMF can be read off the table. The LaMF can also be determined using the TRILUX LIFETIME CALCULATOR (see footnote).

Luminaire maintenance factor LMF = 0,89


Reasons: See table (luminaire group 3) for a very clean non-smoking office, diffuser luminaire.

Room maintenance factor RMF = 0,97

Reasons: See table (d) for the medium-sized, very clean non-smoking office with frequent, intensive cleaning of the room, for direct-distribution luminaires. 
  Maintenance factor    MF = LaMF · LMF · RMF
                               MF = 0,93 · 0,89 · 0,97 = 0,80

with the partial efficiency factors at the end of the period of use (ηLa,eol, LOReol, Ueol) against their initial values (ηLa,i, LORi, Ui).

With three-year installation maintenance, the planning can be based on a maintenance factor of 0,8.

This results in the following initial illuminance to be installed:

Ēi = 500 lx/0,8 = 625 lx (it. 1 in fig.).

The result is the following temporal progression of illuminance:

After 3 years, the time m1 of the first maintenance procedure, the illuminance has decreased to a value of 535 lx (it. 2 in fig.). The luminaires are cleaned, luminaire efficiency rises back to the initial value, utilance remains unchanged.

Illuminance after cleaning the luminaires is

and increases to the value

(it. 3 in fig.)

After 3 more years (after a total of 6 years, m2) illuminance changes as follows: Relative lamp efficiency based on ca. 10,000 hrs of operation is 0,97. Before cleaning, the luminaires have an efficiency reduced by the factor 0,89 due to 3 years of soiling (see  table). Relative utilance is nearly constant and decreases from 0,97 to 0,96 (see table).

After 6 years (before cleaning) the illuminance value is

and illuminance is

(it. 4 in fig.)

After intensive cleaning, the luminaires are back at their initial efficiency.

At the time of planning it is to be assumed that the maintained illuminance will still not drop below 500 lx after six years of operation. Only after 20 years (25,000 operating hours), meaning after ca. 7 maintenance intervals, lamp lumen decrease (degradation) will have progressed to a point where maintained illuminance is no longer attained at the end of the maintenance period.

It is important to observe that

  • the initial value of the installation is actually 625 lx

  • the luminaires are cleaned diligently after 3 years

  • the room is cleaned frequently and intensively and

  • • the room is restored to its initial condition after 6 years.

Figure 3.32: Progression of average illuminance in the example installation

1The TRILUX LIFETIME CALCULATOR facilitates determination of LLMF and LSF for LED luminaires depending on duration of use and ambient temperature as well as conversion of different service life specifications (e.g. from L80 to L70, see also chapter , Service life of LED luminaires). The maintenance factor (MF) can be determined when LMF and RMF of the application are known.