Daniel Vázquez-Moliní

High-efficiency light-emitting diode collimator

We describe an analytical and numerical method to design and optimize LED (light-emitting diode) collimators. The optimization process is confirmed by optical simulations and experimental measurements of a scaled prototype. The collimators definitive geometry and design parameters rely on the LEDs emitting characteristics and the employed collimator material. The resulting parabolic-elliptical-based collimator shows an optimum performance and a compact structure with requirement for mirrored surfaces.

Louvers design for LED displays for sunny days

The use of louvers attached to variable information display needs to be optimized taking into account different intrinsic and extrinsic parameters. The analysis of the performance of the display–louvers system takes into account the location, orientation, and daily and seasonal variations. The observation of the system is divided depending on the distance of observation. The far distance vision performance use the background luminance. The medium distance performance needs the use of the Contrast Sensitivity Function of the eye.

Natural Lighting Systems Based on Dielectric Prismatic Film

The light pipe is a device that can transfer natural light from a building s roof into the depths of the building, this straight construction consist of a reflective closed walled structure (P.D. Swift & G.B. Smith, 1995). Daylight guidance has been one of the mayor areas of innovation in interior lighting in recent years, with the development of light pipes daylight and electric light are simultaneously delivered into a building where they are combined and distributed via luminaries. As a result, the overall wattage of artificial light is reduced and the consumption of electricity decreases (Mayhoub, et al., 2010). The commonest light pipes are reflective mirror guides which use high reflectance aluminium, also fiber optic guides are widely used for illumination purposes. Optical design with new materials like dielectric ones, with regard to their reflection, transmission and absorption is as important as its geometry study.

Lighting quality for aluminum and prismatic light guides

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.

New concentrator multifocal Fresnel lens for improved uniformity: design and characterization

The emergence of high efficiency photovoltaic cells is leading the industry into using solar concentrators in order to reduce costs by decreasing the number of cells used. In this paper Optics department of Universidad Complutense de Madrid has designed a multifocal Fresnel lens of PMMA and has studied the main parameters that have influence on its final function. This has been done by taking into account its manufacturing tolerances. The lens is square shaped with sides measuring 270 mm and it is composed of three different zones based on three different criteria: The central zone has been designed by using paraxial formulation, the intermediate one has been designed based on Fresnel classical formula while the marginal zones purpose is to deflect the light by total internal reflection on prism faces. All three zones have different focal areas and different optical axis so the energy distribution will be more uniform whilst avoiding cell damage caused by hot spots. The design stage is feedback through simulations using a ray tracer software. In order to characterize the lens operation a measure of optical concentration was first taken on different lens areas using an integrating sphere. Finally, the lens performance in terms of concentration and in terms of uniformity at the focal spot was studied by processing the images taken with a CCD camera on a screen placed at the focal plane of the lens.

Thermal influences on optical properties of light-emitting diodes: a semiempirical model

The application of LED technology to fields such as alphanumerical displays and traffic control is continuously increasing. Because the technology is used outdoors, it must be able to operate under various environmental conditions. Like all semiconductor devices, LEDs have properties that change with temperature. We propose a semiempirical model, based on semiconductor solid-state theory, that predicts the changes in the emission spectrum including the effect of temperature changes on the optical properties of the LED, within a range appropriate for outdoor applications (0-40 degrees C). This model permits us to evaluate the changes in the output flux and the chromaticity coordinates of the LED. We checked this model with seven different LEDs.

Modulation transfer function of translucent rough sheets

Rough surfaces in translucent protective sheets are used in imaging systems, such as displays, to decrease specular reflections of external sources. However, they modify the quality of the images formed by transmission. Using a geometric approximation, we have modeled the behavior of rough surfaces in imaging systems. This model provides an analytical expression for the modulation transfer function of rough surfaces.

Optics detailed analysis of an improved collimation system for LED light sources

Throughout present study will be discusses the influence of the manufacturing margins, adjustment precision and ray model accuracy of a collimating LED unit in the overall system performance. It will be also analyzed the angular performance and the collimated in relation to the relative position of the LED and the collimators dimensions. Finally the results will be compared with existing publications in this field.

Skylight: a Hollow Prismatic CPC

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.

Real time 3D photometry

The photometry and radiometry measurement is a well-developed field. The necessity of measuring optical systems performance involves the use of several techniques like Gonio-photometry. The Gonio photometers are a precise measurement tool that is used in the lighting area like office, luminaire head car lighting, concentrator /collimator measurement and all the designed and fabricated optical systems that works with light. There is one disadvantage in this kind of measurements that obtain the intensity polar curves and the total flux of the optical system. In the industry, there are good Gonio photometers that are precise and reliable but they are very expensive and the measurement time is long. In industry the cost can be of minor importance but measuring time that is around 30 minutes is of major importance due to trained staff cost. We have designed a system to measure photometry in real time; it consists in a curved screen to get a huge measurement angle and a CCD. The system to be measured projects light onto the screen and the CCD records a video of the screen obtaining an image of the projected profile. A complex calibration permits to trace screen data (x,y,z) to intensity polar curve (I,αγ). This intensity is obtained in candels (cd) with an image + processing time below one second.