Automotive interior lighting is lighting inside of a car that provides comfort and safety for the driver and passengers.
Automotive interior lighting includes features such as:
Broadly, automotive interior lighting falls into one of three categories:
The driver uses displays and indicators to obtain information, which could be standard dashboard instrumentation information or more complex information from a navigation system, a menu-driven display, or a multimedia device. For display and indicator lighting, the key metrics are color, luminance, and luminance uniformity.
Interior Illumination systems provide light to enable the driver or passengers to see something else. These systems include dome lights, mirror lights to illuminate a face, map and reading lamps, storage lights, and so on. For Illumination systems, the key metrics are the geometry of the illuminated area, illuminance levels, and uniformity. Color can also a factor, both for visibility issues and for custom "mood" lighting.
The primary purposes of accent lighting is to provide styling cues, create a desired ambience and to locate various controls, such as power window controls and radio knobs, and other features, such as cup holders and charging ports, in a darkened cabin. Accent lighting generally has a much lower intensity than interior illumination fixtures since the goal is not to illuminate other objects in the cabin, but just to be visible itself. The main design concerns with this type of lighting are color, visual uniformity, and appropriate light levels.
Unlike specifications for exterior automotive lighting, which come from a government agency (e.g., the ECE in Europe), specifications for interior lighting often come directly from the manufacturer—General Motors, Toyota, Volkswagen, or Hyundai, for example. For a dome lamp, the specifications might include the color for the light, as well as a set of illuminance test points specified in lumens per square meter, or lux, that you measure with a lux meter.
The figure below shows a circular light guide designed for an automotive dome light using the Light Guide Designer in LightTools. The LightTools Optimization Module was used to control the size, shape, and placement of prism textures in the light guide that direct the light from the light source to the target area for the best results.
While the design of something like an illuminated needle for a speedometer may seem simple enough, to do it well the designer must carefully craft the needed elements, and, of course, using the right design tool is a great help.
Typically, items in an instrument cluster such as the speedometer, shift panel (PRNDL), temperature controls, and radio controls have manufacturer test point specifications for luminance (the illumination metric most closely associated with brightness) as well as color (u',v' or x,y color coordinates). Often, the numbers or the needles will have several spread out test points that a quality engineer measures in a dark room with a spectral photometer (or radiometer), which is also called a spot meter.
Usually, the needle is wider at the bottom than it is at the top. A well-engineered needle will have uniform spatial appearance (luminance) along the length. This can be particularly challenging to design because you need a non-linear extraction of light along the needle to achieve the uniform light distribution. Fortunately, LightTools helps you at each design challenge faced in a system like this. The design process may go something like this:
For designing vehicle interior lighting, LightTools illumination design software from Synopsys provides a complete set of design, simulation, and analysis tools for designing superior automotive optical designs.
Left: Side door puddle lamp with logo, designed using the Freeform Designer in LightTools.
Center: Linear light guide created using the Light Guide Designer in LightTools.
Right: Prismatic lens map lamp design created by optimizing prism structures in LightTools.
