Ingineria Iluminatului - Journal of Lighting Engineering - Prof. Florin ...

OPTICAL MODELLING OF A DIFFUSING PRISM LIGHT PIPE USING
THE APILUX SOFTWARE
Oana DOBRE, Gilbert ACHARD
Savoy University, Superior School of Engineer in Chambery (ESIGEC)
Optimisation of the Conception and Engineering of the Environment Laboratory
In the framework of the co-tutored thesis entitled "Contribution to the calculation and design of
interior lighting systems by light pipes", supervised by the thesis directors: Prof. Dr. Eng Cornel
BIANCHI (UTCB, Romania) and Prof. Dr. Eng. Gilbert ACHARD (LOCIE, France), we
characterized photometrically a diffusing prism light pipe of 6 m in length and 10 cm in diameter,
supplied either bilaterally by two identical HQI 70 W lamps, or unilaterally by an 80 W LED lamp.
This paper describes the characterization relating to the computer-simulation phase to determine the
light pipe recurrence laws, and the optical simulation phase in the production of a light pipe model.
1. Light pipe study context
The external horizontal illuminance from the
unobstructed sky in Paris attains a level of
20,000 lux between 07h00 and 17h00 for about
50% of the year.
With a daylight factor DF of 2% in the
central area of a room, we obtain an illuminance
level of 400 lux for the same time periods and
percentage of the year. This level is necessary to
ensure visual comfort in a daylit office. We
observe that it is necessary to use
complementary electric lighting in daytime
periods in room areas situated away from
windows, where the daylight factor is much less
than 2%, and yet there is an overabundance of
natural light outside. The same applies in the
central areas of rooms when the external
illuminance level is below 20,000 lux, that is to
say about 50% of the year, even though in spite
of this reduction there is still an abundance of
external natural light.
Natural light should be better used for the
natural daylighting of office buildings by
dividing its penetration into the rooms into two
parts:
- Windows ensuring the penetration of
natural light to the centre of the rooms. These
natural light inputs will also be managed
according to their thermal contributions, which
are welcome in winter but can be excessive in
summer. The design of the windows and
window components must of course also take
into account problems of dazzling as well as the
acoustic and architectural requirements.
- Light pipes essentially ensuring the
natural lighting of the room areas situated
furthest from the windows. The natural light
must therefore be carried to these less well lit
areas where it will be distributed thanks to the
light pipe extraction function.
The light pipe system will therefore consist
of a first opaque light-carrying section linked to
a natural light source (on the building facade for
example), coupled to a second section
comprising a diffusing prism pipe running
parallel to the wall in which the windows are
mounted (see Figure 1).
INGINERIA ILUMINATULUI 15-2005 5