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2025
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Truck Encyclopedia (10): LED effect is not as good as halogen?
Why are halogen lamps comfortable, but no one buys tall LEDs? Today we will talk about the importance of light in addition to brightness, color temperature.
In the comments of the previous article, it can be seen that many cardholders said that halogen lights look the most comfortable, some think that halogen lights have a high degree of restoration, and some think that halogen lights have strong penetration, etc.
Why are the brightest LEDs not popular, while the older halogen lamps are sought after? Let's talk about the secrets of light.
▎Why do halogen lamps look the most comfortable?
● Spectral frequency hanging LED
Why everyone thinks that halogen lamps look more comfortable than LED lights involves a concept here - spectrum.
To put it simply, after the sunlight passes through the dispersion system (rhombus mirror), we can see that the light is divided into seven colors: purple, blue, cyan, green, yellow, orange, and red.
各种灯泡的光谱功率对比
Let's start by looking at a comparison chart of the spectral power of a set of light bulbs. Although the light produced by humans cannot be compared with the sun, the halogen lamp, as a source of thermal radiation, has a spectrum very close to that of the sun. It can be seen that the spectral continuity of halogen lamps is significantly better than that of LED lamps.
As a cold light source, the spectrum of LED is not a continuous spectrum, and the lighting effect cannot be compared with halogen lamps, which is naturally much worse than halogen lamps in terms of eye comfort.
In addition, the continuous spectrum also makes the external objects more natural and realistic under illumination. LEDs that lack certain spectrum will make the illuminated object look relatively "fake", and the color will be distorted to varying degrees.
This is also the reason why we can advertise the high color rendering of the products in some lamp advertisements.
Color rendering refers to the characteristics of different colors when light sources of different spectrums shine on objects of the same color. The color rendering index (Ra) is usually used to express the color rendering of a light source. The higher the color rendering index of the light source, the better its color rendering performance and the more realistic the color of the object. There will be no discussion here, if card friends are interested, the card family encyclopedia will also be popularized for everyone.
● The strobe of all evil
Another reason that makes LED lights look uncomfortable is PWM dimming. Nowadays, most automotive LED lights are PWM dimming.
The so-called PWM, the full name of Pulse Width Modulation, translates to pulse width modulation, which is the technology of modulating analog signals into pulse waves, and PWM dimming is that LEDs emit light in the form of flashing.
PWM dimming flicker flicker frequency is so fast that it is almost imperceptible to the human eye, and this method is widely used in automotive lighting due to its low cost.
Although most people can't detect flickering above 80Hz, the human eye can still feel the flickering, which can also cause fatigue and headaches for our eyes. Therefore, the reason why cardholders say that halogen lamps are more comfortable than LED lights is probably this.
There was also a news before that a Mercedes-Benz owner in Shanghai was fined for being photographed by the traffic police's law enforcement equipment for flashing taillights. The brake taillights of this Mercedes-Benz sedan are dimmed by PWM.
Similarly, the LED daytime running lights of this Volvo FM are PWM dimming, and the flickering phenomenon can be clearly seen in our video equipment. As a comparison, the xenon headlights in the lens do not have flicker.
Because the frequency of PWM dimming is inconsistent with the frame rate of our video equipment, the strobe that cannot be recognized by the human eye reveals the truth on the camera equipment.
In fact, if you want to solve the problem of PWM dimming and strobe, it is very simple, and DC dimming can be used. The principle of DC dimming is very simple, which is to change the brightness of the LED light by increasing or decreasing the power of the circuit. There is no discussion here, if you want to know about the cardholders, please leave a message in the comment area below, and we will explain it separately according to the situation.
● Color temperature is key
Color temperature is a physical quantity used in illumination optics to define the color of a light source. That is, when a certain blackbody is heated to a certain temperature, and the color of the light emitted by it is the same as the color of the light emitted by a certain light source, the temperature at which the blackbody is heated is called the color temperature of the light source, referred to as color temperature. Its units are expressed in terms of "K" (Kelvin temperature unit).
Color temperature only represents the spectral composition of the light source, not the luminous intensity. The color temperature is high, indicating that there are more shortwave components, and there is a blue-green color; The color temperature is low, which means that the long-wave component is more, and it is reddish and yellow.
Here are some common light source color temperatures:
1800 K: Candle
2800 K: incandescent lamp
3000 K: halogen and yellow fluorescent lamps
5500 K: Daylight at noon
6500 K: white fluorescent lamp
As we mentioned earlier, the spectrum is composed of seven colors of light, such as violet, blue, cyan, green, yellow, orange, and red, after the polychromatic light is divided by the dispersion system.
As you can see from the picture above, red, yellow, and orange have relatively long wavelengths, so red light has the strongest penetration, so the brake lights and fog lights installed at the rear of the car are all red.
However, as lighting, yellow light with a medium wavelength has the best photosensitive effect on the eyes, and also has considerable penetrating power, so the original vehicle headlights, whether xenon or halogen, are more yellowish. The color temperature of this kind of light is about 3000k-5000k, which not only ensures a good lighting effect, but also ensures the light penetration in rain, snow and fog to the greatest extent.
Well, that's all for today's introduction to spectrum and color temperature. Although from a spectral point of view, LED is not as good as halogen and xenon lamps, but the LED lamps of regular manufacturers are not weaker than halogen lamps in terms of color temperature and color rendering, and the advantages of high brightness and low energy consumption of LEDs are incomparable.
When choosing a light bulb, you should consider the brightness of the light and the penetration of color temperature. The headlights with high color temperature may have no other effect at night except to shake the eyes of pedestrians and drivers.
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