10/ 2010
BENNING LUXMETER B
23
4. Illuminance measurements
Practical measurement instruments contain semiconductor sensors which
convert the absorbed light into electric current. For accurate measurements,
luxmeters of the photocell type should be used which have been cosine and
color corrected.
4.1 When and why to measure illuminance
The illuminance measurements should be performed whenever planning or
installing indoor or outdoor lighting.
Too high or too low illuminance could influence the health and cause safety and
psychological problems.
4.2 Some useful hints to ensure accurate measurements
- When measuring illumination at working places, hold the sensor in front (up
to 0.2 m) and parallel to the measured object (table, command plate, desk
etc).
- When measuring horizontal illumination, hold the sensor in front of the
object to be measured so that the window of the sensor faces the ceiling.
The distance between floor and sensor is 0.85 m for routine room measure-
ments and 0.2 m for in-door traffic way measurements.
- During the measurement ensure that light incidence onto the sensor is not
impaired by the operator or any objects not being part of the measurement
(shields or reflections).
- Check the zero setting of the scale when the sensor is fully covered
- Check the condition of the battery in the instrument
- An installation of discharge or fluorescent lamps should be switched on for
some time (15 minutes, if possible) before the measurements are taken in
order to allow the lamps to be completely warmed up. If the luminary is of
the fully enclosed type, even longer stabilization time may be needed.
- The procedure adopted for the measurement process will depend on
whether the space is furnished or unfurnished, occupied or unoccupied. In
some instances the effects of body shadow should be taken into account.
- For planning purposes the nominal illuminance value (see table 4) should
be multiplied by at least x 1.25
- The average illuminance is not allowed to be below x 0.8 of the nominal
value.
- The minimal illuminance must never drop below x 0.6 of the nominal
value.
Other recommendations can be found in DIN 5035.
