Where authenticated data, as mentioned in BS EN 1838:2016, is not available, the following measurement method may be used.
Measurement of illuminance of emergency lighting installations can be very difficult and needs to be carried out with good instrumentation and great care.
All site test work needs to be carried out by simulating a failure of the normal electrical supply and, where practicable, by using the test facilities provided.
It is essential that the light meter used has a photocell having good cosine correction, as a large proportion of the incident light is at glancing angles. The meter needs to be suitable for taking readings at the low illuminances involved, with a minimum range of 0.01 lx to 100 lx and sensitivity of 0.01 lx. Care has to be taken not to overshadow the light sensor, and for this reason a sensor remote from the readout is preferable.
The measurement of the illuminance needs to be made on the same plane as that used for design (see Clause 10).
The effect of stray light (e.g. street lighting or moonlight) can be substantial and, as far as practicable, it needs to be masked out. Where it cannot be excluded, the illuminance from the emergency lighting is obtained by taking readings at appropriate positions inside the building with all interior lighting, including the emergency lighting, switched off. The readings so obtained is then deducted from readings taken at the same positions with the emergency lighting switched on.
The light output of the emergency lighting system will vary with time. The tests therefore need to be completed as quickly as is practicable within the rated duration.
This is particularly relevant in an occupied building or one in daily use as, with discharged batteries, the building could have reduced emergency lighting cover for up to 24 h following the test.
However, that would never be a problem with Commulite and its 9 hour battery duration.
For measurement of emergency lighting on emergency escape routes it is advisable to select for test a number of specific areas likely to have minimum illuminance.
Suggested locations are:
- half-way between luminaires, especially in stairwells;
- where highest luminaire mounting height occurs;
- where widest spacing of luminaires occurs;
- at changes in direction of route;
- at thresholds of doorways forming part of the exit route.
In open areas, tests need to be carried out over the whole of the relevant area (see BS EN 1838:2016). The results of the measurements then need to be checked against design data.
However, when using Commulite systems you can be sure you will have superior light levels everywhere
The rated duration of self-contained luminaires will need to be checked individually. For a central system such as Commulite, it is only necessary to carry out the test at one luminaire, preferably that luminaire subject to the highest voltage drop.
On-site testing will only prove or indicate to some degree the accuracy of the design data, and in most cases the illuminance measured will be higher than the minimum design level.
The minimum value of illuminance is deemed to occur either at 5 s after switch-on or at the end of the battery discharge when the voltage is at a minimum value, and also at the end of useful lamp life.
Such combinations are not usually encountered on site, except where unsatisfactory equipment has been used or maintenance has been poor. When carrying out these tests it is therefore necessary to have data which relates to the lumen output of the luminaire during the lamp/battery life cycle.