**4. Hollow prismatic CPC**

168 Dielectric Material

**Figure 13.** CRI of measured lightguides (cylindrical and rectangular).

will not be studied on the color quantity estimated.

The flux transmitted of the two types of prismatic guides for a wavelength is studied in order to analyze the efficiency of both systems. For this purpose, the distribution characteristics are calculated using a three-dimensional ray tracing. In this case, the lightguides have a 1.49 refractive index for the studied wavelength without absorption losses. Generally, the associated absorption loss in prismatic film is rather low, and taking into account that it is considered the model of light reflection, in this study this parameter

The dimensions of the guides analyzed in the ray tracing study (Fig.14) are the same defined in the theoretical simulation (Fig.8) and the enlargement scale factor of the prism shape is on the order of 10. The light cone input is an extensive emitter with a random distribution of

30º semi angle (θ) which has the same size as the section of the light guide.

**3.3. Flux transfer analysis** 

Compound parabolic concentrator (CPC) is an optical devices used in the solar energy related areas and also in other applications where radiant energy concentration is needed, being defined as one of the first devices that resulted from the practical application of nonimaging optics (Welford and Winston, 1978). Light from a defined range of angles of incidence is reflected by total internal reflection on the parabolic walls of the CPC and concentrated at the exit of the CPC.

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 allows an increase in efficiency compared with the ACPC.

Natural Lighting Systems Based on Dielectric Prismatic Film 171

In this section we analyzed the PCPC by raytracing software to determine the angular transmission, optical efficiency and irradiance distribution on the system exit aperture in a

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

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

a reflectance of 1.0 and the other one, the prismatic CPC designed with PMMA.

3D system, later a comparison between ACPC and PCPC is presented.

**4.1. Ray-tracing: Efficiency of the PCPC compared to ACPC** 

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

through entry 1+2.

**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.

In this section we analyzed the PCPC by raytracing software to determine the angular transmission, optical efficiency and irradiance distribution on the system exit aperture in a 3D system, later a comparison between ACPC and PCPC is presented.
