*4.1.1. Polar Isocandela Plot of ACPC and hollow PCPC*

170 Dielectric Material

The authors propose an innovative 3D hollow prismatic CPC (PCPC) in reverse mode made of a prismatic dielectric material, which has a high efficiency comparing it with aluminium CPC (ACPC). The basic idea is to use a hollow prismatic light guide with CPC shape. In figure 16 (up-left), we can observe the design in 2D geometry in the inverse mode proposal; all the rays entering at the focus of the parabola (F1 and F2) emerge through the exit aperture with the design angle θ. This paper reports 2D, 3D design (Fig. 16) and numerical analysis by ray-tracing software, furthermore experimental results are shown. A prototype has been developed and tested showed in figure 16 (down). The hollow PCPC in reverse mode has an entrance pupil that is small compared to the exit pupil depending on the design angle. This CPC design accepts light in 2 entering the entrance pupil and redirecting it in the CPC design angle. This new concept is made of a prismatic film; this dielectric layer accepts light not only in the entrance pupil (Entry 1) but also through the layer itself. This property

**Figure 16.** The CPC profile (up-left) with a ray tracing showing the design angle and the maximum input angle of design θ, 3D hollow HCPC 30º software design (up-right) and the experimental prototype (down)

in which the reflector surface is a prismatic film supported by eight polycarbonate ribs.

allows an increase in efficiency compared with the ACPC.

The polar intensity diagram provides the shape of the light distribution of both parabolic systems. Figure 17 (a) shows isocandela plot representing the ACPC intensity and angular distribution. The 17 (b) illustrations show the isocandela plot for PCPC when light enter through entry 1+2.

Natural Lighting Systems Based on Dielectric Prismatic Film 173

(7)

Ray-tracing is processed for two kinds of CPCs, one designed with standard aluminum with

Computed efficiency is obtained by tracing collimated rays in 5º angle intervals for both

The comparison of PCPC and ACPC collectors is shown in figure 18; it indicates the effects of incidence angles and the efficiency of the PCPC. To compare both systems it is used collimated light at different angles. The flux obtained in the entry 1 (*Φ*) is used to calculate

> *entry*1 *exitpupil*

When it is analysed the efficiency obtained in both systems adding the prismatic surface of the PCPC (entry1+entry2) to 85º, it is observed the improvement with regard to the ACPC,

 

 

The PCPC accepts light out of this entry pupil Entry 1 so *η* can be higher that 100%.

**Figure 18.** Output flux HPCPC VS output flux HPCPC 30º cone using entry1 and entry2

The efficiency of the PCPC to compare the outflow of 30º cone (\*) (entry1+entry2) with regard to the efficiency of entry 1 it is evaluated. There is a clear profit for incidence angles ranging from 0º to 35º, though it is necessary to improve the efficiency for the higher

It is necessary to investigate how the PCPC is working when light enters in the entry pupil

reaching a 600 % higher efficiency flux than an ACPC.

a reflectance of 100 % and the other one, designed with dielectric prismatic film.

systems and computing the obtained flux at the exit pupil of the system.

**5. Efficiency comparative** 

the final efficiency (*η*),

incidence angles.

(entry 1) as it is done in ACPC.

**Figure 17.** The polar intensity diagram provides the shape of the light distribution to the exit of both parabolic systems

## **5. Efficiency comparative**

172 Dielectric Material

parabolic systems

**Figure 17.** The polar intensity diagram provides the shape of the light distribution to the exit of both

Ray-tracing is processed for two kinds of CPCs, one designed with standard aluminum with a reflectance of 100 % and the other one, designed with dielectric prismatic film.

Computed efficiency is obtained by tracing collimated rays in 5º angle intervals for both systems and computing the obtained flux at the exit pupil of the system.

The comparison of PCPC and ACPC collectors is shown in figure 18; it indicates the effects of incidence angles and the efficiency of the PCPC. To compare both systems it is used collimated light at different angles. The flux obtained in the entry 1 (*Φ*) is used to calculate the final efficiency (*η*),

$$\eta = \frac{\phi\_{entry1}}{\phi\_{exitupill}}\tag{7}$$

The PCPC accepts light out of this entry pupil Entry 1 so *η* can be higher that 100%.

When it is analysed the efficiency obtained in both systems adding the prismatic surface of the PCPC (entry1+entry2) to 85º, it is observed the improvement with regard to the ACPC, reaching a 600 % higher efficiency flux than an ACPC.

**Figure 18.** Output flux HPCPC VS output flux HPCPC 30º cone using entry1 and entry2

The efficiency of the PCPC to compare the outflow of 30º cone (\*) (entry1+entry2) with regard to the efficiency of entry 1 it is evaluated. There is a clear profit for incidence angles ranging from 0º to 35º, though it is necessary to improve the efficiency for the higher incidence angles.

It is necessary to investigate how the PCPC is working when light enters in the entry pupil (entry 1) as it is done in ACPC.

Natural Lighting Systems Based on Dielectric Prismatic Film 175

A CCD video photometer (Radiant Imaging Prometric 1400) is used to measure output light distribution in exit pupil with a Lambertian screen (Fig.21). We measure output light in two experimental assemblies changing the incidence angle between 0º and 75º increasing the source angle in steps of 15º. Firstly, we evaluate entry 1, and secondly entry 1+2 is evaluated.

**Figure 21.** Schematic diagram of experimental setup The HPCPC has the following parameters: input aperture diameter (entry1): 88 mm; output aperture diameter (Lambertian screen): 187 mm, L: 4000 mm,

Normalized light distribution map onto exit pupil is shown in the figures 22 to 28. The (a) figure represents the illuminance map obtained with the ray tracing software, the (b) figure represents the map obtained with the experimental setup. Figures 22 to 24 show data for

using entry 1 and 25 to 28 show data using entry 1+entry 2 for some light angles.

**Figure 22.** 15º entry1. (a) Raytracing simulation, (b) Experimental measurement.

**6. Experimental measures** 

d: 260 mm.

**Figure 19.** ACPC VS PCPC using entry 1.

The ACPC works better than PCPC as the incidence angle increases if we use only entry 1 in the prismatic PCPC. Figure 19 show this behaviour for different incidence angles. The TIR that suffers light beam in the outer surface of the PCPC is not happening when incidence angle increases, this behavior explains the decrease of efficiency according to the incidence angle increases The division of the beam showed in figure 20 (b) is due to the prismatic effect when light reach the film in the outer side as shown basic raytrace in figure 1a.

**Figure 20.** Examples of collimated light entering entry 1 30º (a) and entry 2 30º (b).

The light guiding after PCPC is a good alternative to light far away from the collecting system, the use of a hollow light guide is demonstrated as a good way to transport light, and new bending systems show a good way to reach all the lighting necessities.
