The Basic Concept and Relevant Parameters of LED Lighting

In the 19th century, humanity entered the era of electrical lighting. After years of development, we are now in the era of the fourth-generation solid-state light source – LED lighting. Let’s explore the knowledge related to LED lighting together.

Definition: LED is the abbreviation for Light Emitting Diode. In Chinese, it is translated as “发光二极管” (fāguāng èrjíguǎn).

Based on the different semiconductor materials used, LEDs emit light in different colors, including traditional ones such as red, green, orange, yellow, and blue. Consequently, they are called blue LED, among others. White light is a combination of colors, so white LEDs are modulated based on the aforementioned colors.

Basic parameters for lighting applications:

Luminous Flux:

It refers to the radiation power perceived by the human eye, i.e., the ratio of the brightness of the light emitted by the source. The unit is lumen (lm). For example, a 40W incandescent bulb has a nominal luminous flux of 360 lm, a 40W daylight fluorescent lamp has a nominal luminous flux of 2100 lm, and a 400W standard high-pressure sodium lamp can reach a luminous flux of 48000 lm.

Luminous Efficacy:

It is the ratio of luminous flux to electrical power and is generally expressed in lm/W. Luminous efficacy represents the energy-saving characteristics of the light source and is an important indicator for evaluating the performance of modern light sources.

Radiant Intensity and Light Intensity Distribution:

LED radiant intensity indicates its strength in a specific direction. Due to the different spatial angles, the light intensity of LEDs varies greatly, which leads us to understand the light intensity distribution characteristics of LEDs. This parameter holds significant practical significance as it directly affects the minimum viewing angle of LED display devices.

Wavelength:

For the spectral characteristics of LEDs, we mainly focus on their monochromaticity and whether colors such as red, yellow, blue, green, and white LEDs are pure. In many situations, such as in traffic signal lights, color requirements are relatively strict. However, it has been observed that some LED signal lights in China have a bluish-green color or a deep red color. Therefore, it is necessary and meaningful for us to conduct specialized research on the spectral characteristics of LEDs.

Color Temperature:

The light that a human eye perceives is composed of the overlapping spectra of seven colors. However, some spectra tend to be more blue, while others tend to be more red. Color temperature is a method specifically used to measure and calculate the color components of light. The unit is Kelvin (K). Different light sources have different color temperatures, resulting in different light colors and feelings:

<3300K: Warm (white with a reddish hue) – stable, warm

3000-5000K: Intermediate (white) – refreshing

5000K: Cool (white with a bluish hue) – cold

Color Rendering Index (CRI):

The ability of a light source to display the colors of objects is known as color rendering. It is determined by comparing the appearance of objects under the light source with the same color temperature as a reference or standard light source (incandescent lamp or daylight). There are two types of color rendering: faithful color rendering, which requires a light source with a high color rendering index (Ra) close to 100 to correctly represent the true colors of objects, and effect color rendering, which emphasizes specific colors to enhance the aesthetics of life. By using the method of adding colors, the effect color rendering can be strengthened. Using a low-color temperature light source can make red more vibrant, using a medium-color temperature light source can give a cool feeling to blue, and using a high-color temperature light source can give objects a cold sensation.

Ra Index (CRI) Color Rendering Level General Application:

90-100: 1A Excellent – suitable for places that require precise color contrast.

80-89: 1B Good – suitable for places that require accurate color judgment.

60-79: 2 Normal – suitable for places that require moderate color rendering.

40-59: 3 Fair – suitable for places with low requirements for color rendering and small color differences.

20-39: 4 Poor – suitable for places where specific color rendering is not required.