Conocimientos básicos sobre LED

Whether you are manufacturing or purchasing LED light strips, understanding the fundamentals of LEDs is crucial.

As the core light-emitting component, the characteristics of LEDs directly determine the performance of the light strips. For manufacturers, this knowledge guides LED chip selection, circuit design, and process control. For buyers, it is key to distinguish between high-quality and low-quality products and avoid the trap of “misleading specifications.”

Only by understanding the underlying principles of LEDs can one ensure that LED light strips meet expectations in core metrics such as brightness, energy efficiency, and lifespan. Below, I will take you through some basic knowledge about LEDs.

What is an LED?

‌LED (light-emitting diode)‌ is a semiconductor solid-state light source‌. The semiconductor chip consists of two parts: one is a P-type semiconductor, where holes dominate, and the other is an N-type semiconductor, where electrons dominate. When these two semiconductors are connected, they form a P-N junction. When current flows through the wire and acts on the chip, electrons are pushed toward the P-type region. In the P-type region, electrons recombine with holes, releasing energy in the form of photons. This process is the principle behind LED lighting. The wavelength of light, which determines its color, is determined by the materials used to form the P-N junction.

LEDs can directly emit red, yellow, blue, green, cyan, orange, violet, and white light. An LED package is a plastic housing containing an LED chip and a phosphor. The LED chip is a semiconductor material that emits light (blue light), while the phosphor material converts some of this light into green and red wavelengths. The resulting white light is emitted from the LED package. The packaging material plays a significant role in the heat dissipation of LEDs (e.g., PPA, PCT, and ceramic).

LED light sources offer advantages such as low-voltage power supply, low energy consumption, high adaptability, high stability, short response time, environmental friendliness, and multi-color emission, making them an ideal choice for modern lighting.

What are the main types of LED packaging?

LED packaging forms include through-hole DIP, surface-mount SMD, and integrated COB.

‌Through-hole (DIP)‌: DIP LED packaging has a cylindrical shape with long leads, with the chip located inside the plastic housing. DIP LEDs have two parallel metal leads. While some products still use this design today, compared to newer LED packaging, DIP LEDs have lower light output and color rendering index. These LEDs are primarily used for signal lights and decorative applications, such as Christmas light strings. However, they have poor heat dissipation and low luminous efficacy (<50 lm/W) and are gradually being phased out.

Surface-Mounted (SMD): SMD LEDs were developed after DIP LEDs. Compared to DIP LEDs, SMD LEDs offer higher luminous efficacy and lower power consumption. Compared to DIP LEDs, they have a smaller design, lower height, longer lifespan, reduced energy consumption by up to 75%, and lower maintenance costs. Mainstream surface-mount types (such as 2835, 3030, 5050, etc.) feature a compact size, superior heat dissipation, and light efficiency >120 lm/W, making them widely used in lighting fixtures. For more information about SMD LEDs, please read the blog: SMD3528 vs SMD2835 vs SMD5050: ¿Qué tira de luz LED es la mejor para la iluminación comercial y arquitectónica?

Integrated (COB): COB packaging involves placing several chips (typically 9 or more) on an aluminum substrate, integrating more chips into a limited space to achieve higher luminous intensity in a smaller area. This design occupies less space while maximizing lighting potential. This technology eliminates the need for a base and soldering, reducing assembly time by nearly one-third and lowering costs. COB types are typically used in high-efficiency lighting fixtures such as industrial lights, streetlights, parking lots, and open spaces requiring large illumination areas. Due to their high brightness per unit area, they also generate significant heat, so they must be used with large heat sinks. For more information on the differences between COB LEDs and SMD LEDs, please read the blog: Diferencia entre LED SMD y LED COB: ¿Cuál es mejor?

What is the Color Rendering Index (CRI)?

The Color Rendering Index (CRI) is a measure of a light source’s ability to accurately reproduce the colors of objects. It primarily describes how closely the colors of objects appear under a light source compared to their colors under natural light (such as sunlight). The higher the CRI value, the stronger the light source’s ability to reproduce colors, and the more closely the colors of objects appear under that light source to resemble their colors under natural light. For more information about CRI, please read the blog: ¿Qué importancia tiene el índice de reproducción cromática de las tiras de luz LED?

Light sources with the same color temperature may have different spectral compositions. Light sources with broader spectral compositions are more likely to provide better color rendering quality. When a light source’s spectrum lacks or has very little of the dominant wavelength reflected by an object under a reference light source, it can cause significant color differences. The greater the color difference, the poorer the light source’s color rendering performance for that color. The CRI coefficient is a widely used method for evaluating a light source’s color rendering performance.

The CIE defines the Planckian radiator as the reference light source, setting its color rendering index to 100, and specifies eight color samples. If, under a light source, the color of the sample matches that under the reference light source, the light source’s color rendering index is 100; if the color changes, the light source’s color rendering index is below 100.

The color rendering index is of great importance in lighting design and applications, particularly in scenarios requiring accurate color reproduction of objects, such as art galleries, photography studios, and medical facilities. In these settings, selecting light sources with high color rendering indices ensures the authenticity and accuracy of object colors. It is important to note that the color rendering index is not the sole criterion for evaluating light source quality; it primarily focuses on the light source’s ability to reproduce colors. When selecting a light source, other factors such as brightness, color temperature, and energy efficiency should also be considered comprehensively.

What is color temperature?

Color temperature is a unit of measurement that indicates the color components contained in light. Theoretically, the color temperature of a blackbody refers to the color it exhibits when heated from absolute zero (-273°C). When the color of a light source matches the color of a blackbody at a certain temperature, the absolute temperature of that blackbody is referred to as the color temperature of the light source. It is also known as “colorimetric temperature.” The unit is kelvin (K).

The color range of commonly used lighting is approximately 2700K to 6500K. The lower the color temperature value, the more reddish the color; the higher the value, the more bluish the color; intermediate values appear whiter. Color temperatures between 2200K and 3750K are referred to as warm white light; 4000K to 5000K is neutral white; and 5700K to 8000K is cool white light.

1. Color temperature and color coordinates have a one-to-many relationship; the same color temperature can have different X and Y values.

2. In other words, it can only be called color temperature when it falls on the blackbody radiation curve.

3. The same color temperature can produce different color perceptions.

For more information on color temperature, please read the blog:

3000K vs 4000K vs 5000K vs 6000K: ¿Cuál es la diferencia?
Comparación de la temperatura de color de la iluminación LED: 5000K vs. 6000K
Comparación de la temperatura de color de la iluminación LED: 4000K vs. 5000K
Comparación de la temperatura de color de la iluminación LED: 3000K vs. 4000K
Comparación de la temperatura de color de la iluminación LED: 2700K frente a 3000K

What is correlated color temperature?

When the chromaticity point of a light source is not on the blackbody trajectory, and the chromaticity of the light source is closest to that of a blackbody at a certain temperature, the absolute temperature of that blackbody is the correlated color temperature (CCT) of the light source. The unit is kelvin (K).

In everyday use, we see the test data from spectroscopic instruments. This is the correlated color temperature (CCT), not the color temperature. What is the difference between them? Of course there is: the color temperature of a light source is the temperature of an ideal blackbody radiator whose emitted light corresponds to the color of the light source. In other words, only when it falls on the blackbody radiation line can it be called color temperature.

Color temperature is defined on the standard line, while correlated color temperature is defined relative to this standard color temperature. The white light we produce may not exactly align with the standard color temperature line; instead, we find the “closest” point and read its color temperature, which is referred to as the “correlated color temperature.”

Therefore, even if the correlated color temperature is the same, such as 3000K, if the color tolerance is 7 steps, the color temperature range can be 2870-3220K, with a difference of nearly 350K, which may result in significant visual differences.

What is color tolerance?

Color tolerance is used to characterize the difference between the X and Y values calculated by the color measurement system software and the standard light source. The smaller the value, the closer the product’s color coordinates are to the standard values. The smaller the gap between the light source’s spectrum and the standard spectrum, the higher the accuracy and the purer the color of the light.

You may be confused: there are many XY combinations for the same color temperature. What color temperature and coordinates meet the sensory comfort requirements of solid-state lighting and the human eye? How can this issue be resolved? To address this issue, the concept of color tolerance must be introduced.

Due to the different densities of red, green, and blue phosphors, color temperature differences can easily occur during production. Once such differences arise, they must be adjusted through color tolerance to ensure the light color of the lamp. As a lighting source, white LED lighting should adhere to color tolerance standards to guide the development and application of new white LED lighting sources.

The Relationship Between Color Temperature and Color Tolerance

Color temperature is a unit of measurement that indicates the color components present in light. Theoretically, the color temperature of a blackbody refers to the color it emits when heated from absolute zero (-273°C). When a blackbody is heated to a certain temperature and the color of the light it emits matches the color of light emitted by a specific light source, the temperature at which the blackbody is heated is referred to as the color temperature of that light source, i.e., color temperature, with the unit of measurement being “K.” The smaller the value, the more reddish the color; the larger the value, the more bluish the color; intermediate values tend toward white. The typical color temperature range for lighting in normal use is approximately 2700K to 6500K, corresponding to warm white light and neutral white light.

The standard spectrum changes with color temperature. For the same light source, if the standard spectrum differs, the color difference also varies. However, during measurement, a standard light color analysis system typically automatically identifies the color temperature range of the measured light source to determine the color temperature value of the standard spectrum. At the same color temperature, if the reference standard spectrum is consistent but the X and Y color coordinates differ, the color difference will also vary.

Color coordinates and color difference are related. Color coordinates are calculated based on the color chart, and color difference is the difference between the actual measured color coordinates and the standard. Color difference is the difference between the product’s X and Y values and the standard light source’s X and Y values. The smaller the distance, the lower the SDCM. For more information about SDCM, please read the blog: Todo sobre SDCM para tiras de LED

We use SDCM to evaluate light color, so how do we measure this parameter? Typically, a spectrophotometer like the one shown in the figure below can be used to test color temperature and color difference.

Factors Affecting Color Tolerance

1) Chip Variation: LED chips from different batches or models have inherent differences in their light-emitting characteristics, leading to shifts in color coordinates.

2) Process Influence: Uneven distribution of phosphor caused by dispensing, with adhesive layer thickness deviations exceeding 5%, significantly reduces color coordinate consistency.

3) Material effects: The material composition, ratio, and coating uniformity of phosphors directly affect spectral distribution and color temperature consistency.

4) Instrumentation effects: For example, differences between spectrophotometers and integrating spheres, or between different models of the same instrument, can result in varying measurement outcomes. Additionally, discrepancies in critical parameters set by customers versus original equipment manufacturers (OEMs), such as differing integration times for integrating spheres, can also introduce measurement errors.

5) Thermal management impact: If the lamp’s thermal management is insufficient, temperature increases can cause color drift. LED light-emitting materials exhibit significant temperature-dependent characteristics; as the emission temperature rises, the emission spectrum shifts toward the red, the emission peak broadens, and at a certain temperature, the emission ceases. To ensure the lamp’s lifespan and luminous flux meet requirements, the junction temperature of the LED lamp must be maintained within a specific range.

6) Current effects: As the drive current changes, the properties of the light-emitting material are also affected. The higher the light-emitting stability, the smaller the color temperature effect and the smaller the color tolerance.

Why do LED lights with the same color temperature appear to have different colors?

Some might wonder why, despite having the same 3000K color temperature, the lights exhibit different colors, suggesting that color temperature tolerances may not effectively address the issue. Indeed, within the specified color temperature tolerance range, LED lighting manufacturers have consistently faced challenges related to color temperature inconsistency. This phenomenon not only manifests as significant color differences despite identical color temperature values, known as “same temperature, different color,” but also exists in cases where the colors are similar but the tested color temperature values are vastly different, known as “same color, different temperature.”

As shown in the figure below, the three points A, B, and C on the blue line belong to the same 3000K color temperature. Point A is exactly 3000K warm white light, while point B is slightly greenish at 3050K, and point C is slightly reddish at 2950K. They differ by approximately 50K. Although the color temperature difference is not significant, the actual perceived colors are distinct.

Furthermore, as color temperature decreases, the phenomena of “same temperature, different color” and “same color, different temperature” become increasingly pronounced. Therefore, if you want your product colors to achieve consistency, we must use color difference tolerance (SDCM) to address this. If the color center point of the product coincides with the color difference tolerance center point, then color difference tolerance can be used to characterize color differences; the larger the color difference tolerance, the greater the color difference.

Let’s first look at the following comparison of color difference images for 3000K color temperature LED lights: If the two color coordinates fall within a 2-step ellipse, the human eye can barely discern the difference between them. If it’s a 5-step ellipse, the color difference becomes noticeable; if it’s a 3-step ellipse, the difference between the boundary color and the central color is not immediately obvious at a glance. Therefore, for 3000K color temperature lighting, if the goal is to achieve near-zero color difference, the color tolerance should typically be set within 3 steps.

From the above analysis, it is clear how important color difference is. If color difference is not controlled, the LED light strips produced may exhibit inconsistent color when illuminated. Imagine a linear light strip; if there are color differences between LEDs, they can easily be detected by the human eye. When the color of the entire light strip is inconsistent, it results in a poor lighting experience. To achieve high-quality lighting effects, you should purchase light strips with higher luminous efficacy and smaller SDCM values.

LED Industry Color Tolerance Standards

In 1942, scientist MacAdam conducted experiments on 25 colors using related principles, measuring 5 to 9 relative sides of each color point and recording the two points at which they could distinguish color differences. The result was an ellipse of varying size and length, known as the MacAdam ellipse.

Within the MacAdam ellipse, even if there are color differences, our eyes cannot detect them. However, once the color falls outside this ellipse, we can easily discern the color difference. Therefore, within the MacAdam ellipse, we can consider the colors of the points to be consistent.

The size of the MacAdam ellipse is also referred to as the Standard Deviation of Color Matching (SDCM), an important metric for assessing color consistency. By increasing the ratio of the major and minor axes of the MacAdam ellipse, we can obtain MacAdam ellipses of different orders, such as second-order, third-order, and so on. These ellipses of different orders provide us with more detailed standards for evaluating color consistency.

1. European and American color temperature X.Y coordinate standard points

The main color difference standards currently in use are the North American ANSI standard and the IEC European standard. The corresponding color difference center points are summarized as follows:

2. Energy Star and European color difference standard ranges

● Energy Star ANSI C78.376, color difference ≤7 SDCM, divided into regions according to LED characteristics.

● European Union IEC 60081 standard, color tolerance ≤7 SDCM, with LED regions defined according to luminous technical requirements.

Resumen

After the above introduction, I believe everyone now has a better understanding of LED color temperature.

SignliteLED is a high-tech enterprise specializing in the research, development, and manufacturing of LED strip lights, with technological innovation and rigorous testing as its core competencies. The company has a complete R&D system, ensuring that the color temperature deviation of all LED strip lights is controlled within 3 steps for warm color temperatures and within 5 steps for cool white color temperatures.

From chip selection to driver circuit design, everything is controlled in-house. The product range includes flexible LED light strips, COB LED light strips, LED neon light strips, and other high-value-added categories. By equipping the company with spectrophotometers, constant temperature and humidity test chambers, and other devices, it has established over 20 testing standards, including 72-hour aging tests and IP waterproof ratings, to ensure the stability and reliability of product performance. If you are interested in these products, please contact our business team.