Cylindrical prismatic hollow light guides are able to transmit daylight properly into the spaces of a building in which
natural light has a difficult access. Transmission through the guide depends on the optical characteristics of the
material, the shape of the guide and the fidelity of the geometry in prisms structure. It is important to analyse the
micro-structure prism imperfections of the surfaces such as the existence of a curved area on peaks prism which
modify the behaviour of the prism film; these imperfections, change the optical path and therefore the rays are
directed to other directions instead of undergoing total internal reflections. In this paper, several cylindrical guides
made of transparent dielectric material characterized with an absorption factor have been developed. A numerical
analysis has been carried out by software tools to analyse the flux distribution in the light guidance system
comparing its efficiency by optical analysis in different simulations. These simulations include high reproductively
prism related to the light pipe’s material and optical properties including a study of the impact of imperfect
geometry which is necessary to allow rigorous comparisons with the experimental simulations. The simulated results
have been compared with experimental data obtained through real scale analysis. The experimental measurements
have revealed effectiveness of 66.7 % in the aspect ratio of 30.
The use of high reflectance aluminum lighting guides is most frequently used material for actual natural lighting systems.
Spectral Reflectance over the entire length of a light guide changes the color of the output light at the end of the guide.
When light guides are made of a prismatic film, the influence of the reflectance is minimizing and absortance is not
important when the sheets are thin. Color Rendering index and color temperature will be important parameters in order to
evaluate Lighting quality and therefore in Museums, office buildings and production centers to get the normative
approval. In this paper a theoretical simulation and 3D ray tracing for aluminum and prismatic light guides of different
shapes (rectangular and cylindrical) and lengths over the entire visible spectrum are studied. Output light color
temperature related to several illuminants and CRI are evaluated for the simulated aluminum and prismatic light guides.
Thus, prismatic light guides seem more robust in lighting quality maintenance regardless of conditionals like angle
acceptance for TIR guiding, aluminum guides are efficient and maintain light quality only for short distances.
Many applications involve the use of a compound parabolic concentrator (CPC) like, natural lighting, thermal
applications, optics for illuminators, optical fibre coupling and solar energy. The use of a CPC in reverse mode
for natural lighting gives the chance to use it as a lighting skylight in ceilings because light output is controlled
inside the design angle, on the contrary having a low flux transfer ratio because of the reduced area of the
entrance pupil regarding exit pupil. The authors propose an innovative 3D hollow prismatic CPC (HPCPC) made
of a dielectric material, which has a high efficiency comparing it with aluminium CPC. The basic idea is to use a
hollow prismatic light guide with CPC shape. This paper reports 2D, 3D design and numerical analysis by raytracing
software, also experimental results are shown. The system works almost like a true CPC when light enters
through standard entrance pupil and also collect light that enters outside entrance pupil. Performance and
efficiency of the prismatic CPC is in average 300% higher than standard aluminium CPC for collimated light in a
range from 0º to 85º. A prototype has been developed and tested.
Transmission of light through a 90 degrees elbow in a hollow light guide is an important step in the development of
natural lighting applications. In this paper we present a new design that has more than 260% higher efficiency in flux
transfer than a standard bending system for hollow and aluminum light guides. The clue of this new system is to
minimize the light angle at the output of the elbow, in such way that it is possible to guide light at higher distances
because of the fewer reflections in the light guide.
The system works properly for prismatic light guides but is also suitable for aluminum guides where the reduction of
reflections permit the use of cheaper aluminum or the increase in length maintaining flux transfer. Also this reduction of
reflections in aluminum light guide derives in less change of chromatic coordinates.