Six important indicators of LED light source performance and their relationship

To determine whether an LED light source is what we need, we usually use the integrating sphere to test, 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 coordinates. , color temperature and color rendering index (Ra). (In fact, there are many other parameters such as: peak wavelength, dominant wavelength, dark current, CRI, etc.) Today we will explore the significance of these six parameters for the light source and their interaction with each other.

Luminous flux : Luminous flux refers to the radiant power that can be felt by the human eye, that is, the total radiated power emitted by the LED, in lumens (lm). Luminous flux is the direct measurement quantity and the most intuitive physical quantity to judge the brightness of LED.

Voltage : The voltage is the potential difference between the positive and negative poles of the LED lamp, which is the direct measurement, in volts (V). It is related to the voltage level of the chip used by the LED.

Light effect : luminous efficiency, that is, the ratio of all luminous flux emitted by the light source to the total input power, is the calculated amount, unit: lm/W. For LEDs, the input electrical energy is mainly used for illuminating and heating, and the high luminous efficiency indicates that the part used for heat generation is small, and it is also a good expression of heat dissipation.

Through the meaning of the above three, it is not difficult to see the relationship. When it is determined that the current is used, the luminous efficacy of the LED is actually determined by the luminous flux and the voltage. When the luminous flux is high, the luminous efficiency is high. As for the current large-scale adoption of blue-light-emitting yellow-green fluorescent light-emitting methods, since the common voltage of a single-core of a blue-light chip is about 3V, it is a relatively stable value, and the improvement of light efficiency is mainly achieved by increasing the luminous flux.

Color coordinates : The coordinates of the color, that is, the position of the color in the chromaticity diagram, is the measured quantity. In the commonly used CIE 1931 standard colorimetric system, coordinates are represented by two values ​​of x, y. The value of x can be considered to be the degree of red light in the spectrum, and the value of y is considered to be the degree of green light.

Color temperature : The physical quantity of light color is measured. When the radiation of the absolute black body is exactly the same as the radiation of the light source in the visible region, the temperature of the black body is called the color temperature of the light source. The color temperature is the measured quantity, but at the same time it can be calculated by the color coordinates.

Color rendering index (Ra) : used to describe the ability of a light source to restore the color of an object. It is determined by comparison of the appearance color of the object under a standard light source. Our color rendering index is actually the calculation of eight light color measurements of the integrating sphere for light gray red, dark gray yellow, saturated yellow green, medium yellow green, light blue green, light blue, light purple blue and reddish purple. average of. It can be found that R9, which is often referred to as saturated red, is often included, and because some lighting requires more red light (such as meat lighting), R9 is often used as an important parameter to evaluate LEDs.

Color chart

The color temperature can be calculated by color coordinates, but a closer look at the chromaticity diagram reveals that the same color temperature can correspond to many pairs of color coordinates, and a pair of color coordinates only correspond to one color temperature, so the color coordinates are used to describe the color of the light source. To be exact. The display index itself has nothing to do with color coordinates and color temperature, but the higher the color temperature, the colder the light color, the less red component in the light source, the harder it is, and the red light for low color temperature warm light. It has many components, wide spectral coverage, and closer to the spectrum of natural light. The color rendering index can naturally be higher. This is also the reason why LEDs above 95Ra are low in color temperature.