The change of LED in automotive lighting applications in the role of (2)

Human factors issues 4. LED

LED source is very different from most of the incandescent lamp now used in automotive lighting applications:

LED has a higher luminous efficiency than the filament source (L m/W), which means that they can use the same amount of energy to produce a higher strength or wider beam pattern, or with lower energy requirements to produce similar light output.

Narrowband spectral output - color LED can produce highly saturated color appearance, and the incandescent lamp as light source, filter need to create color lighting (Figure 3).

- white phosphor converted LED can produce higher than the correlated color temperature of incandescent lamp (CCT), there will be more blue appearance.

LED has a very fast response time: 10-20 ns, including yttrium aluminum garnet (YAG) phosphor decay time, while the incandescent lamp is about 80-250 Ms.

Figure 3: yellow and red LED (filtering) and the spectral distribution of the light source filament.

Luminosity and chroma and time characteristics of the LED light source may also affect the ability of the driver to see the road and respond to potential danger. For vehicle headlight system, short wavelength spectrum of typical InGaN devices and YAG blue phosphor phosphor converted white LED combined with the distribution of a greater proportion based on (blue) light (Figure 4). This difference and driving the visual function, because when driving at night, the asphalt pavement brightness between 0.1 CD /m2 and 1 cd/m2, the risk is carried out by visual inspection in the eyes of rod and cone visual receptor.

Figure 4: white LED and (unfiltered) filament light source spectral distribution.

However, photometric measurements, such as illumination, brightness (LX) (cd/m2) (CD), luminous intensity and luminous flux (LM), completely based on the spectral response of eye cone receptor. The cone receptor specifically for Daytime Outdoor and indoor illumination conditions watch, usually between 10 and 1000 cd/m2. There are obvious differences of measuring light and we look at the way, because in general, rod-shaped receptor than pyramidal receptor on short wavelengths (such as blue and green light) are more sensitive. Therefore, the usual photometry (LX, cd/m2, CD and LM) will underestimate the driver's ability to see things in the night LED source.

The International Commission on illumination (CIE) recently released a unified photometric measurement system, to quantify the rods and cones in the relative role of night. Therefore, LED can be used to produce light than incandescent light low level of 20% to 30% can get the equivalent night vision function.

According to the brightness model developed by Rea et al., another visual response is better than LED filament light source brightness induction on the street. This induction seems to increase the sensitivity of short wavelength. Figure 5 shows the use of halogen, HID and LED light source brightness prediction of road.

However, the relatively high short wavelength light white LED lighting in power spectrum may also have some negative effects on possible vehicle lighting. When the different colors of the headlights have the same conventional spectrophotometry, the influence is not affected by the glare illumination spectral content. The discomfort glare, this is not the case.

Like the street like brightness induction, discomfort glare sensitivity to short wavelength increase. It is not clear whether increased discomfort glare or affect the safety of driving in a large extent. There is evidence that when the driver encountered discomfort glare from the front headlights, they are more likely to have the driving behavior, such as head movements increased, it is believed may increase the risk of collision.

On the visual detection of vehicle lights, because the LED startup time is much shorter than the incandescent lamp, so LED has some advantages, especially for vehicle brake lamp. Bullough that can use the driver's eyes light induction threshold quantity, predicting the emergence of chromatic light signal (such as brake lights or turn signal) visual reaction time. When the first open the tungsten filament, the lighting is relatively increased, and the need for 250 ms to reach full brightness. LED is almost instantaneous start time, and can quickly produce a critical amount of light. Therefore, compared with the same nominal color luminous intensity and peak filament source, visual shorter reaction time caused by LED.

It is important that the deceleration rate of vehicle braking and brake lights on (the brake pedal) associated with action, so light the shorter rise time can be behind the driver to provide nearly 7 meters of parking distance, although the distance is very small, but sometimes actually ten valid.

Figure 5: the light source luminosity equal (halogen, HID and LED) in relative brightness on the surface of the road lighting.

5 the problem of energy and environment

Compared with the filament light source, automotive lighting system using LED source has a higher luminous efficiency, can significantly reduce the power demand. In a separate study, Hamm and Schoettle to estimate the typical power source routine filament vehicle lighting system and LED lighting system. They have different lighting and signal function of the estimated average are summarized in table 4. Table 4 is according to the driving mode are estimated for each type of general lighting system using time value. At the same time, table 4 lists the filament source vehicle lighting system and LED lighting system lighting in total energy use.

Table 4: power and energy consumption estimation of filament lamps and LED automotive lighting system

Lighting energy assuming a gasoline powered car per kWh equivalent to 1.29 kg of carbon dioxide emissions, to the filament lamp LED is expected to total annual energy consumption will be reduced to 27.4 kwh, equivalent to an annual reduction of two per car about 35 kilograms of oxidation