Trends and Immaturity
With the increasing popularity and expanding applications of exterior lighting systems in Automotive, front and rear facet lighting in particular.
What makes the facet lighting fascinating recently, is that it makes communication to pedestrians and surrounding cars possible by displaying or pixelating messages, which potentially brings the security to a higher level. Another important feature is that the facet lighting offers limitless flexibility for car makers to highlight their design signature on a larger area of the car body by an elegant light design.
Unlike the conventional front light and rear lighting system, whose design and development would strictly follow the existing road standard, the front or rear facet lighting system involves human perception, besides the usual car lighting functions: illumination or signaling. So a common question among the tier one developers is, how to qualify and quantify the new lighting system quality when there isn't an available road standard, or when the car makers don't have a universal requirement defined?
Perceived Quality
The pedestrian communicating feature brought by facet lighting adds a new dimension into the assessment and qualification of the lighting system: Perceived Quality.
The conventional lighting system for illumination usually uses illumination, unit in lux, to define the system capability; and signaling system uses light intensity, unit in candela, to quantify the required light level.
However when talking about perception to humans, eye comfort is an unignorable criteria that needs to be considered, especially the light level and color at night should be well controlled. Furthermore, readability of the displayed message is another key element.
Eye comfort : Glare should be avoided by limiting parameters like, Maximum luminance etc.
Readability : Clear exhibition of message would be secured by contrast level between the enlightened area and the background, homogeneity, uniformity etc.
Quality Assessment framework
Below three blocks framework proposed accordingly:
Appearance Requirement ：Aesthetic needs and dimensional regulations
- Defines the dimension of the enlighten area and back grounded or grid area. It needs to fulfill the rear lighting regulation at the first priority.
- Defines number of pixels according to specific features and power consumption needs ect.
- Defines colors, textures and other visual appearance effects.
Photometric Requirement ：Minimum Photometric Distribution to fulfil Lit Aspect
- Defines lighting Intensity Distribution (LID)
- Defines visibility angle
Lit Aspect Requirement ：from Must-to-Have to Nice-to-Have
- Defines Luminance level range
- Defines Perceived Quality
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