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

Figure 8 Isolux curves of half the light pipe with
light injected by 2 HQI70 W lamps (distance 1.3 m)
b) To produce the polar indicators (see Figures
9, 10 and 11), i.e. curves of intensity
distribution as a function of emission angle,
which can be put into a standard format (IES,
PHILLUM, etc.) and be used in the databases of
certain lighting simulation software programs.
At half the maximum intensity we obtain the
emission or aperture angle of the studied lamps
and light pipes, and this value is used to
calculate the efficiency of the light pipe. Figure
11 shows the transverse indicators of the light
pipe (in planes perpendicular to its optical axis)
at varying distances from the source lamp.
Figure 9 Polar indicators of the HQI70W Halogen
lamp
Figure 10 Polar indicators of the 80W LED lamp
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INGINERIA ILUMINATULUI 15-2005
Figure 11 Transverse polar indicators of the light
pipe
c) To calculate the emitted fluxes and
efficiencies using the utilization factor (standard
NE C71-121 of the UTE Union Technique de
l'Electricité) and the excitance (or emittance)
method that takes into account the interreflections
on the walls of the room in which the
studied light pipe is situated. The efficiency of
the tube was verified using Lorne A.
Whitehead's method corrected by a ray tracking
approach.
d) To determine the light pipe recurrence laws (put
into analytical, exponential and matrix forms).
The characteristic curves of the lamps and
the light pipe were used to validate an optical
model of a light pipe designed using the
APILUX software that will be described later.
4. Light pipe recurrence laws – analytical form
In order to understand the light pipe extraction
system and be able to produce an optical model,
we established the recurrence laws relating to
the extracted fluxes and the fluxes carried
within the light pipe divided into unit sections
for both the ideal case without losses (see
Figure 12), and the true case with losses (see
Figure 13) considered to be distributed
uniformly along the pipe.
Figure 12 General recurrence laws – ideal case
without losses