What is an LED?

LED is the abbreviation of light emitting diode, which is translated as "light emitting diode" in Chinese. It is an electronic device that can convert electric energy into light energy and has the characteristics of a diode. At present, different light emitting diodes can emit light with different wavelengths from infrared to blue light, and there are also white LEDs coated with fluorescent powder to convert blue light into white light.

Color and technology of LED: Different materials can produce photons with different energy, thus controlling the wavelength of light emitted by LED, that is, spectrum or color. The material of the first LED in history was gallium arsenide (As) (Ga), and the light emitted was infrared spectrum. Another commonly used LED material is gallium phosphide (Ga), which emits green light.

Because gallium, arsenic and phosphorus are used in the manufacturing process, these LEDs are usually called ternary LEDs. The blue led of GaN, the green LED of GaP and the infrared LED of GaAs are called binary LEDs. At present, the latest technology is a quaternary LED made of AlGaInN quaternary materials mixed with aluminum (Al), calcium (Ca), indium (In) and nitrogen (N), which can cover all the spectral ranges of visible light and part of ultraviolet light.

Luminous intensity:

Luminous intensity is measured by lux, lumen and candlelight.

1CD (candle light) refers to the luminous intensity of a completely radiated object per sixtieth square centimeter at the freezing point of platinum.

1L (lumen) refers to the luminous flux of 1 CD candle shining on a plane with a distance of 1cm and an area of 1cm.

1Lux (lux) refers to the illuminance where the luminous flux of 1L is evenly distributed on the area of 1m2.

The active luminous body generally adopts the luminous intensity unit candle CD, such as incandescent lamp and LED. Reflecting or penetrating objects use luminous flux unit lumen L, such as liquid crystal projector; Luminance unit Lux is generally used in photography and other fields. The three units of measurement are equivalent in value, but they need to be understood from different angles. For example, if the brightness (luminous flux) of a liquid crystal projector is 65,438+0,600 lumens, and its projection size on the total reflection screen is 60 inches (65,438+0 square meters), its illuminance is 65,438+0,600 lux, assuming that its light outlet is 65,438+0 cm away from the light source and its light outlet area is 65. However, due to the loss of light propagation, the loss of reflective or light-transmitting film and the uneven distribution of light, the brightness of a real LCD projector will be greatly reduced, and the efficiency of 50% is generally good.

In practical use, data units that are easy to map or change direction are often used in light intensity calculation. For LED display screen, which is an active luminous body, CD/ m2 is generally used as the luminous intensity unit, and the observation angle is used as an auxiliary parameter, which is equivalent to the illuminance unit lux on the screen surface. Multiply this value by the effective display area of the screen to get the luminous intensity of the whole screen at the perfect angle. Assuming that the luminous intensity of each pixel in the screen is constant in the corresponding space, this value can also be regarded as the luminous flux of the whole screen. Generally, the brightness of outdoor LED display screen must reach more than 4000 CD// m2, in order to have ideal display effect in the sun. Ordinary indoor LED, the maximum brightness is about 700~2000 CD//m2.

The luminous intensity of a single LED is in the unit of CD, and it is equipped with viewing angle parameters, and the luminous intensity has nothing to do with the color of LED. The luminous intensity of a single tube ranges from several MCD to five thousand MCD. The luminous intensity given by the LED manufacturer refers to the point where the LED lights up at 20mA current, and the luminous intensity is the highest at the perfect angle and center. The shape of the top lens and the position of the LED chip from the top lens determine the LED viewing angle and light intensity distribution. Generally speaking, the larger the viewing angle of the same LED, the smaller the maximum luminous intensity, but the cumulative luminous flux on the whole solid hemisphere remains unchanged.

When a plurality of LEDs are closely and regularly arranged, their luminous spheres overlap each other, resulting in a relatively uniform luminous intensity distribution in the whole luminous plane. When calculating the luminous intensity of the display screen, it is necessary to multiply the maximum point luminous intensity provided by the manufacturer by 30% ~ 90% as the average luminous intensity of a single tube according to the LED viewing angle and LED emission density.

Generally, the light-emitting life of LED is very long, and the manufacturer generally marks it as 100000 hours or more. In fact, we should also pay attention to the brightness decay period of LED, which has a great relationship with the material technology and manufacturers of LED production. Generally, if economic conditions permit, international brands with slow brightness attenuation such as Riya should be selected.

Color matching and white balance:

White is a mixture of red, green and blue according to the brightness ratio. When the brightness of green is 69%, the brightness of red is 2 1%, and the brightness of blue is 10%, people will feel pure white after mixed colors. However, the chromaticity coordinates of LED red, green and blue can't achieve the effect of full color spectrum due to process flow and other reasons, and controlling the brightness of primary colors including deviation from primary colors to get white light is called color matching.

Before the color matching of full-color LED display screen, in order to achieve the best brightness and the lowest cost, LED devices with the luminous intensity of three primary colors of about 3:6: 1 should be selected as far as possible to form pixels.

White balance requires that the three primary colors are still pure white at the same gray adjustment value.

Primary colors, primary colors:

Primary color refers to the basic color that can synthesize various colors. The primary colors of colored light are red, green and blue. The following figure is a spectrum table, and the three vertices in the table are ideal primary color wavelengths. If the primary colors deviate, the area where colors can be synthesized will be reduced, and the triangle in the spectrum table will also be reduced. Visually, the color will not only be biased, but also the richness will be reduced.

The red, green and blue light emitted by LED can be roughly divided into purplish red, pure red, orange red, orange yellow, yellow-green, pure green, green, blue-green, pure blue and blue-purple. Orange, yellow-green, blue-purple are much cheaper than pure red, pure green and pure blue. Green is the most important of the three primary colors, because it occupies 69% of the brightness of white and is in the center of the horizontal color arrangement table. So when weighing the relationship between color purity and price, green is the key consideration.

Glossary of LED lighting:

Wavelength: The color intensity of light can be described by data, which is called wavelength. The wavelength of visible light ranges from 380 to 780 nanometers. Unit: nanometer (nm)

Brightness: Brightness refers to the brightness of an object and is defined as the luminous intensity per unit area. Unit: Nite

Light intensity: refers to the brightness of the light source. That is, it represents the physical quantity of visible light radiation intensity emitted by a light source in a certain direction and range. Unit: candle light (cd)

Luminous flux: the total amount of visible light emitted by a light source per second. Unit: lumen (Lm)

Light efficiency: the luminous flux emitted by the light source divided by the power of the light source. It is an important index to measure the energy saving of light source. Unit: lumens per watt (Lm/w).

Color rendering: the degree to which a light source presents an object, that is, the fidelity of color. Usually called "color rendering index". Unit: Ra.

Color temperature: at a certain temperature, the color of the light emitted by the light source is the same as that radiated by the blackbody, and the temperature of the blackbody is called the color temperature of the light source. Unit: Kelvin (K).

Glare: the visual discomfort caused by objects with extremely high brightness or strong brightness contrast in the field of vision is called glare, which is an important factor affecting the lighting quality.

Synchronization: Two or more LED lamps can work normally in a programmed synchronization mode within a specified time, and synchronization is the basic requirement for LED lamps to achieve coordinated changes.

Protection grade: IP protection grade is classified according to the dust-proof and moisture-proof characteristics of lamps and consists of two numbers. The first number represents the level of dust prevention and foreign body intrusion prevention of lamps and lanterns (0-6), and the second number represents the sealing degree of lamps and lanterns against moisture and water intrusion (0-8). The higher the number, the higher the protection level.