The automotive industry is very competitive. About 30% of the world's cars are produced in China, and Japan is 10%. A total of 72 million vehicles are produced worldwide each year. Now, consider how many different designs are created each year. I would say at least a few thousand. Every car has at least 2 lights, and most have additional lights on the rear windshield. This article will introduce you to the production steps of the light guide strip sample of the automobile headlight. What is a light pipe? The light guide is made of PMMA (i.e. acrylic) or PC, when the light source is placed at one end of the tube, the whole object will be transmitted along the entire length of the tube. Rays are essentially reflected from the guide and the serrated surface along its axis. The larger the angle of incidence, the brighter the shaft, as shown in the figure below. Design and Requirements Most light guide designs are created to accentuate the silhouette of the lamp. This can be achieved by making the tube the desired shape and then placing the LED diodes at one end of the tube at a 30-45 degree angle, or by placing many smaller diodes under the whole tube. There are some requirements for light pipes, as they must transmit light with at least 50% efficiency. in order to do this. The light guide must be a fully transparent part with no air bubbles or irregularities in its structure. In order to reflect and transmit enough light, the surface of the pipe must be very smooth. The pipe surface finish can usually reach Ra 0.32μm! Vacuum overmolding injection molding is great for mass production, but its molds are too expensive for small batches. That's why vacuum molding is the most common method of production. The surface finish of the final part depends on the quality of the master pattern. Master patterns can be made by CNC machining or 3D printing, and then post-processed to achieve the desired quality. CNC machining usually does not have high precision in vacuum complex molding, and its surface finish is not as good as that of glass. This is why CNC machining is often the first choice for producing precise light guide strips. Precision Machining and Post-Processing This stage requires precise 5-axis milling and is ideal for machining optical components with complex geometries. Afterwards, the PMMA is machined into a glass-like structure using very thin, pointed diamond tools. For maximum surface uniformity, polishing is used. According to the initial quality of the parts, the grain size of the sandpaper is usually between 400# and 600#, and the special polishing paste is finished at 1500# to 2000#. The result is a transparent surface with the optical quality of a simple glass, but with much higher tensile strength and less brittleness. Such light guiding strip samples can withstand substantial impacts. Testing In order to estimate the efficiency of the constructed light guide, testing must be performed. Metering is the main process here. Photometry now allows us to estimate lighting and the way it affects human perception. The device used for such measurements consisted of a prototype hand lamp fixed on a special turntable, a screen with a window for measuring only a part of the light, and a photometer behind this window. A spectrometer is sometimes installed to estimate the 'warmth' of the light. The light bulb is mounted on the turntable and turned on. The measuring device begins to read the light as a result. Turn the light's dial to move the photometer closer to or away from the window. The resulting estimate fully characterizes the luminous flux of the light guide. Note that if your light guides are delivering less light than you want, you can avoid redesigning and remanufacturing the tubing. Simply fix the light source in such a way that the angle between the surface of the tube and the main direction of the light is smaller. Light will enter at a greater angle and will reflect more frequently on the surface of the tube, therefore, more light will also pass through the plastic.