Introduction

Have you ever had customers ask about amber, red, blue, or other colored LED chips? Why do they need chips in these colors? It’s because they serve different purposes: red light is commonly used in plant lighting, amber light is often used in port lighting, while blue light is generally avoided in many settings and is typically found only in stage lighting (RGB or RGBW fixtures). LEDs actually emit blue light initially. When this blue light interacts with the yellow phosphor inside the LED chip, it produces light of other colors, ultimately resulting in white light. White light consists of blue, green, yellow, and orange light; when the proportions of these colors are adjusted, the light can emit a specific color. This article primarily explains what visible light wavelength is, what the light spectrum is (i.e., spectral power distribution across the visible wavelength range), why streetlight projects (ZGSM street lights) require amber lights or reduced blue light, and how we achieve specific lighting colors.

What’s visible light wavelength?

Light is a form of electromagnetic radiation, and visible light is made up of electromagnetic waves that are visible to the human eye. Visible light triggers visual perception in humans and animals, thereby producing vision; the wavelength range of visible light typically falls between 400 and 780 nanometers (nm). Wavelengths shorter than 400 nanometers (ultraviolet light) and longer than 780 nanometers (infrared light) are not visible to the naked eye and do not create any visual effect in lighting applications. Not only is excessive exposure to ultraviolet light invisible to the naked eye, but it can also damage the eyes or cause skin burns; the same is true of infrared light, which is the principle behind traditional bathroom heaters. The visible light wavelength is made up of six colors in order (violet, blue, green, yellow, orange and red) in order from the shortest to the longest wavelength. The 400–450 nm range corresponds to the violet and deep blue bands; 450–500 nm is the typical blue light emission range for LED fixtures; 500–570 nm corresponds to the green light; 570–590 nm corresponds to the yellow light; 590–610 nm corresponds to the orange light; 610–780 nm corresponds to the red light. When LED luminaires undergo IES LM-79 optical testing, spectral power distribution data is typically collected over the light wavelength range of 380 nm to 780 nm. Although light in the 380–400 nm range is invisible to the naked eye, the instrument still records it. These data essentially represent the radiant power values corresponding to each wavelength; they are not only used to describe the spectral shape but also directly influence key metrics such as correlated color temperature, color rendering index (More about CRI), and CIE color coordinates. Here’s a straightforward example: An LED lamp with a color temperature of 3000K has very little blue light, with energy primarily concentrated in the yellow and red regions; conversely, a 4000K LED lamp is exactly the opposite—it has a high proportion of blue light, while yellow and red light are much weaker. Therefore, the spectral power distribution not only reveals the lamp’s color temperature characteristics but also serves as a crucial basis for assessing blue light hazard.

Spectral power distribution over visible light wavelength

The spectral power distribution within the visible light wavelength range (commonly referred to as the spectral power distribution, or SPD) refers to the amount of optical radiation (power) emitted by a light source at each specific wavelength within the visible spectrum. The spectral power distribution over the visible wavelength range is frequently cited in the IES LM-79 reports for LED luminaires. If you examine an LM-79 report closely, you will find that it primarily consists of two parts of luminaire testing. One part is performed using a goniophotometer to measure the luminaire’s luminous intensity distribution (What’s light distribution?), while the other part is performed using an integrating-sphere photometer to measure the spherical average radiance (SPD). Data is generally collected within the range of 380 nanometers to 780 nanometers. As shown in the figure below, by measuring the radiance at different wavelengths, we obtain a set of data (a curve). In the figure below, the horizontal axis represents wavelength (nm, mainly 400-780nm visible light wavelength), and the vertical axis represents radiant power (W). It’s not just about how bright the light is; more importantly, it’s about the “composition” of the light. The SPD can also be used to calculate photometric and colorimetric indices. For example, if the SPD shows very low energy in the red light segment, the R9 value will be poor, causing red jerseys on the field to appear grayish and indistinct. Additionally, for some monochromatic LED chips—such as amber and red—color rendering is not considered as a metric because their spectral power distribution is too narrow. Similarly, for low-blue-light LED chips, the Ra value tends to be somewhat lower due to the low blue light component; however, they still have numerous practical applications.

Why we need amber lights for street lights/post top lights?

Minimizing ecological disruption and protecting nocturnal wildlife

Studies have shown that the long wavelength of amber light (approximately 590 nanometers) has the least effect on the navigation and reproductive behavior of nocturnal insects, migratory birds, sea turtles and other animals. Unlike conventional area and site lighting, which typically emits white light, amber outdoor light (including amber street lights and post top lights) contains a smaller percentage of blue light, thus decreasing its impact on hatchling sea turtles that rely on moonlight to find their way to the ocean. It also effectively reduces insect phototaxis, helps preserve the food chain and is the preferred lighting solution to replace traditional white light in ecologically sensitive areas.

Reducing light pollution and preserving dark skies

Amber light has a lot less blue light in it and so it produces less Rayleigh scattering in our atmosphere, and is less likely to contribute to the “glow” that lights up the night sky. For example, Darksky (More about Darksky) requires streetlights and post-top lights in some areas to have a CCT of less than 3000K. As we know, light with this color temperature is often yellowish. The organization also requires that the lighting fixtures do not emit light upwards, all in an effort to minimize the adverse effects of artificial lighting on astronomical observations.

Enhancing visibility in adverse weather

Due to its extremely low blue light content, amber light produces weaker Rayleigh scattering in the atmosphere and is less likely to create the “glow” that illuminates the night sky. For example, Darksky requires that streetlights and post-top lights (ZGSM post top lights) in specific areas have a CCT below 3000K, and as we know, light at this color temperature tends to be yellowish. At the same time, the organization also requires that luminaires not emit upward light; these measures are all designed to minimize the negative impact of artificial lighting on astronomical observations.

So how we get the specific color of lighting?

ZGSM offers LED lighting solutions in a variety of colors. While white light remains our core business, the SPD (spectral power distribution) of these fixtures can vary significantly. We also provide solutions for RGB applications, such as floodlights, sports field lights (ZGSM sports lighting solutions), and amber streetlights. We invite you to contact us to find the ideal lighting products for your needs and work together to protect our environment.

SPDs with different CCTs (Including less blue light options)

Taking Lumileds’ LED chips as an example, we compared the spectral power distributions (SPDs) of white LED chips with different CCTs and found significant differences in their spectral distributions. The spectrum of 2200K–3000K warm white light is dominated by long-wavelength red and orange light, with extremely low energy in the blue light band, resulting in a warm yellow undertone; 4000K–5000K neutral white light has a balanced ratio of red, green, and blue bands, with a flat spectrum and no obvious color bias, making it suitable for various color-mixing applications; For cool white light at 5700K and above, the short-wavelength blue light peak is prominent, resulting in a bluish-white, cool-toned light. A custom SPD designed for low blue light significantly reduces the harmful blue light range at 415–450 nm and moderately increases the proportion of red and green light, providing a softer visual experience at the same color temperature. Although the color temperature is the same—2200K or 2700K—we can see that the blue light peak around 415–450 nm has virtually disappeared (How to reduce blue light in LED lighting?). Therefore, while color temperature can serve as a reference for blue light content, the SPD results should ultimately be the determining factor (the figure below shows the spectral power distribution results for CCTs of 3000K and 4000K). In commercial lighting, different white light bases directly alter the base color of the mixed light. To adjust cool white light to a warmer tone, a large number of red LEDs are required for neutralization, while adjusting warm white light to a cooler tone requires adding blue and green LEDs. A customized SPD can correct the base color in advance, reducing the difficulty of adjusting the ratio of colored LEDs.

Differences in spectral power distribution among color LED Chips

Taking Lumileds LEDs as an example, we compared the spectral power distributions (SPDs) of the brand’s red, green, blue, and amber monochromatic LEDs. As shown in the figure below, the spectral waveforms of each type of LED are well-defined, with energy concentrated in the specific visible light wavelength bands corresponding to their respective colors; the spectral boundaries are clean and sharp, with no excess stray spectral components. Thanks to the factory-level spectral sorting and binning process (Something about LED binning) for monochromatic LEDs, variations in SPD between individual devices are significantly minimized, effectively ensuring consistent light color and stable performance across an entire batch of lighting fixtures. Red LEDs are concentrated in the long-wavelength range of 620–660 nm, with no blue light interference; when combined with warm white, they produce a highly saturated orange-pink hue. Green LEDs have a main peak at 510–550 nm, are pure with no red cast, and are suitable for mint and turquoise tones. Blue LEDs are concentrated in the short-wavelength range of 440–470 nm and emit a strong cool sensation when lit alone. Amber LEDs fall between red and green, helping to soften the harshness of white light. The SPD bands of each monochromatic LED do not overlap, making them widely used in plant grow lights. By adjusting the drive current (LED driver and its main parameters), we can modify the light energy of each band; when combined with white light spectra of different CCTs, this approach meets the specific wavelength requirements of particular plants. Although amber light can be used for road lighting, its luminous efficiency is significantly lower than that of conventional white LEDs, so it is best suited as a supplementary lighting solution.

ZGSM lighting solutions

Summary

This article focuses on visible light wavelengths and spectral power distribution (SPD) in LED lighting, providing a systematic answer to the practical question of “why customers need chips in specific colors, such as amber and red.” The article first defines the visible light spectrum as 380–780 nm and explains the principle by which LEDs initially emit blue light, which is then converted to white light via phosphors. It emphasizes that the SPD not only describes the spectral composition but also directly influences color temperature, color rendering index, and blue light hazard assessments. In the section on spectral distribution, the article uses LM-79 test data as an example to illustrate that the SPD serves as the computational basis for photometric and colorimetric metrics. By comparing the SPDs of white light with different CCTs, it reveals how low-blue-light custom solutions attenuate the harmful 415–450 nm wavelength band and enhance visual comfort. Regarding amber light, the article argues for its necessity in streetlights and garden lights from three perspectives: reducing ecological disruption, minimizing light pollution (How to reduce light pollution?), and enhancing penetration through rain and fog, while also pointing out its limitation of relatively low color rendering. Regarding the achievement of specific light colors, the article compares the SPD differences among pure-color LED chips—such as red, green, blue, and amber—explaining how their narrow-bandwidth, high-purity characteristics are widely applied in plant lighting and mixed-light color tuning. It also emphasizes that adjusting the drive current and sorting LED chips by bin ensures color accuracy and batch consistency. Overall, this article provides lighting professionals with systematic guidance ranging from wavelength principles to product selection and application.

Related Products

Related Blogs

Related Cases

People also ask

Author introduction