To judge whether an LED light source is what we need, we usually use an integrating sphere for testing, and then analyze according to the test data. The general integrating sphere can give the following six important parameters: luminous flux, luminous efficiency, voltage, color coordinate, color temperature and color rendering index (RA). (in fact, there are many other parameters, such as peak wavelength, main wavelength, dark current, CRI, etc.) today we will discuss the significance of these six parameters to the light source and their mutual influence.

Luminous flux: luminous flux refers to the radiation power that can be felt by human eyes, that is, the total radiation power emitted by the LED, unit: lumen (LM). Luminous flux is a direct measurement quantity and the most intuitive physical quantity to judge the brightness of LED.

Voltage: voltage is the potential difference between the positive and negative electrodes of LED lamp beads, which is a direct measurement, unit: volts (V). Which is related to the voltage level of the chip used by the LED.

Luminous efficiency: luminous efficiency, i.e. the ratio of the total luminous flux emitted by the light source to the total power input, is the calculated quantity, unit: LM / W. For LEDs, the input power is mainly used for light emission and heat generation. If the light efficiency is high, it means that there are few parts used for heat generation, which is also a manifestation of good heat dissipation.

It is not difficult to see the relationship between the above three meanings. When the use current is determined, the light efficiency of LED is actually determined by the luminous flux and voltage. If the luminous flux is high and the voltage is low, the light efficiency is high. As for the current large-scale blue chip coated with yellow green fluorescence, since the single core voltage of blue chip is generally around 3V, which is a relatively stable value, the improvement of light efficiency mainly depends on the improvement of luminous flux.

Color coordinate: the coordinate of color, that is, the position of color in the chromaticity diagram, which is the measurement quantity. In the commonly used CIE1931 standard colorimetric system, the coordinates are represented by X and Y values. The x value can be considered as the degree of red light in the spectrum, and the y value is considered as the degree of green light.

Color temperature: a physical quantity that measures the color of light. When the radiation of the absolute blackbody and the radiation of the light source in the visible region are identical, the temperature of the blackbody is called the color temperature of the light source. Color temperature is a measured quantity, but it can be calculated by color coordinates.

Color rendering index (RA): it is used to describe the ability of the light source to restore the color of the object. It is determined by comparing the appearance color of the object under the standard light source. Our color rendering index is actually the average value calculated by the integrating sphere for the eight light color measurements of light gray red, dark gray yellow, saturated yellow green, medium yellow green, light blue green, light blue, light purple blue and light red purple. It can be found that it does not include saturated red, that is, R9. Since some lighting requires more red light (such as meat lighting), R9 is often used as an important parameter to evaluate LEDs.

The color temperature can be calculated by the color coordinates, but when you carefully observe the chromaticity chart, you will find that the same color temperature can correspond to many pairs of color coordinates, while a pair of color coordinates only correspond to one color temperature. Therefore, it is more accurate to use color coordinates to describe the color of the light source. The display index itself has nothing to do with the color coordinate and color temperature. However, when the color temperature is higher and the light color is cooler, the red component in the light source is less, and the display index is difficult to be very high. For the warm light source with low color temperature, the red component is more, the spectrum coverage is wide, and the spectrum closer to the natural light, the color index can naturally be higher. This is also the reason why LEDs above 95ra on the market have a low color temperature.