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 E_i (index "i" for "initial"), the intended use of the room as well as further basic parameters are considered:

The partial maintenance factors add up to:

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).

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

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 (η_La,eol, LOR_eol, U_eol) against their initial values (η_La,i, LOR_i, U_i).

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:

Ē_i = 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.

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.