LED packaging materials include LED chips, brackets, glue, phosphors, bonding wires, etc. Each material determines the performance and parameter value of LED lamp beads, so about the basic photoelectric parameters of LED lamp beads, such as luminous flux , Light intensity, illuminance, brightness (brightness), radiant power, color temperature, color rendering, etc., are not introduced here, we need to focus on understanding the relationship between these parameters.
The quality identification of LED lamp beads requires spectral analysis and photoelectric analysis. If the quality requirements are strict, it also needs to pass the LM79 and LM80 tests. The manufacturer needs to complete the LED lamp bead quality assessment before mass production. The seller must ask the manufacturer to provide LED lamps. Only the quality assessment report can provide the promise to the customer.
The general test parameters of point light sources are: color temperature, display index Ra, luminous flux, light efficiency, junction voltage U, X, Y value.
LED lamp bead quality assessment is the main method of establishing product credit. LED lamp bead quality assessment can be conducted in a third-party test online store. Let’s talk about the correlation of these basic parameters.
Parameters related to luminous flux:
Luminous flux is a parameter to measure the brightness of light. The greater the luminous flux, the brighter the lamp beads. The accurate luminous flux requires professional optical instruments to test. The parameters that affect the luminous flux of LED lamp beads are:
1) The size of the chip area. At the same current, the larger the chip area, the higher the luminous flux. The chip size is expressed in inch mil, 1mil=0.0254mm.
2) The size of the current passing through the chip. Under the same chip area, the larger the passing current, the higher the luminous flux. The LED is a current device. It has a rated current and cannot be arbitrarily increased. For example, the current of the 2835 package is nominally 60 mA. .
3) The size of the radiated power of the chip, the same size of the chip, there are also radiated power levels, the greater the radiated power value, the higher the luminous flux.
4) It is related to packaging materials and packaging technology. Packaging materials include phosphors, glue, brackets, chip bonding wire materials, etc. Packaging technology refers to the impact of packaging equipment accuracy and equipment performance on packaging quality. The better the packaging material, the packaging equipment The higher the level, the higher the luminous flux of the packaged LED lamp.
5) The higher the operating temperature, the lower the luminous flux, and the higher the operating temperature, the easier the LED device is damaged.
Parameters related to luminous efficiency:
Luminous efficiency is an indicator to measure whether the light source is energy-saving. The unit is the lumens per watt (lm/w), which indicates how much luminous flux can be generated for each watt of electricity consumed. The higher the value, the more energy-efficient. The reason why LED lighting replaces fluorescent lamps and incandescent The light is because the light efficiency of the LED light source is 2-10 times higher than that of the traditional light source.
According to the law of conservation of energy, the higher the luminous efficiency, the more electrical energy converted into light energy and the smaller the amount of heat converted.
The parameters that affect light efficiency are:
1) The parameters that affect the luminous flux all affect the luminous efficacy. The higher the luminous flux, the higher the luminous efficacy.
2) The driving current also affects the light effect. The smaller the driving current of the lamp beads of the same package specification, the greater the luminous effect.
3) The lower the PN junction voltage of the LED, the higher the luminous efficacy.
4) The more effective the heat dissipation structure of the package, the higher the luminous effect.
5) The higher the operating temperature, the lower the luminous efficiency of the lamp beads.
Parameters related to lamp life:
Generally, the operating temperature of semiconductor current devices determines the life of the device. We often see that the high-power transistors in electronic equipment are fixed on the heat sink. The life of LED lamp beads also mainly depends on the operating temperature. The life of lamp beads can generally be Expressed as lamp bead failure (not bright) and light decay (luminous flux reduction).
The main factor that affects the life of LED lamp beads is light decay. Light decay is expressed by the luminous flux maintenance rate. Usually, during the warranty period, the light attenuation cannot be less than 30% of the initial luminous flux.
1) Ambient temperature and working temperature, under the same heat dissipation conditions, the higher the environment and working temperature, the shorter the life of the lamp bead.
2) The smaller the drive current, the longer the life of the lamp beads.
3) The better the quality of the packaging material, the longer the life of the lamp beads.
4) The higher the efficiency of the heat dissipation structure, the longer the life of the lamp beads.
5) The higher the electrostatic protection level of the chip and the package, the longer the life of the lamp bead.
Parameters related to color temperature and color rendering index:
The light color of white light is expressed by the color temperature, the unit is the absolute temperature K (Kelvin), the color temperature of the white light LED is divided based on the Brank curve (the horizontal black line in the figure), because the color coordinate XY value of each light source is not It must fall on the Brank curve, usually expressed in terms of correlated color temperature (CCT).
CCT value is the vertical projection point of the color coordinate XY point and the Brank curve, and the LED color temperature distribution is shown in the following figure:
The ability of artificial white light to reduce the natural color of an object is measured by the color rendering index (CRI). This method uses the contrast between the medium brightness value and the chroma to determine the CRI, as shown in the following figure:
Averaging R1 to R8 is the average color rendering index (Ra). The CRI test is often R9 or even too low, and sometimes a negative value appears, which means that the white light produced by the LED lacks red radiation, and the low value of R9 will affect R1-R8 , Leading to a decrease in the average value of Ra. For the warm color temperature range, Ra is feasible to measure the color rendering of the LED light source. For the LED light source with a high color temperature range, Ra will have a certain distortion when measuring the color rendering.
As the national standard stipulates that Ra is used to judge color rendering, we can only use this parameter as a reference. For white light with a color temperature above 4000K, do not rely too much on Ra to evaluate color rendering. Visual contrast of the same color temperature should be used. The effect is better than the dependency test Ra. Of course, for professionals, the conclusion can be drawn from the values of R1-R15.
The color temperature and color rendering of white light are the main indicators to measure the quality of lighting. The consistency of the color temperature of the lamp beads packaged in the same batch will be different. They can only be used after color separation. The color temperature mainly examines the drift of consistency and color temperature. Color, it must be at least 65 or more to be used in lighting.
The parameters that affect the color temperature and color rendering of lamp beads are:
1) Phosphor quality and ratio, the better the quality of the phosphor, the better the color temperature consistency, the smaller the color temperature drift, the more scientific the phosphor ratio, the better the color rendering.
2) The greater the drive current, the color temperature will drift to a higher color temperature.
3) The worse the phosphor quality, the easier the color temperature drifts, and the light decay is also easy to occur.
4) The operating temperature also affects the color temperature drift.
5) The worse the chip quality, the worse the color temperature consistency.
6) For products of the same material and packaging process, the consistency of high color temperature (such as 6500K) is easier to do, and low color temperature (such as 3000K) requires a smaller color temperature segment.
LED lighting products are greatly affected by the choice of LED lamp beads. When manufacturing and selling LED lighting products, more attention should be paid to the quality identification of LED lamp beads. LED lighting products are generally composed of multiple LED lamp beads. To obscure the poor quality of lamp beads, product manufacturers need to start from the analysis of lamp beads parameters to identify the quality connotation of the product and minimize the operational risk.