Analysis of color drift mechanism of warm white LED light source

1 Introduction

With the continuous improvement of environmental protection requirements, lighting products have also begun to develop in an energy-saving and efficient manner. Traditional lighting products have low luminous efficiency and short lifespan, which is not conducive to long-term development, which prepares the market for LED lighting. The efficacy of LED lamps can reach 8 to 10 times that of incandescent lamps, 2 times for energy-saving lamps, and the lifetime can reach 5000-100,000 hours, which has great advantages compared with traditional lighting products. With the continuous development of technology and the continuous promotion of products, the price of LED lighting products has been continuously decreasing, and it has begun to enter the general lighting market.

Different spaces require different light colors. Choosing the right light source is also an important part of the lamp selection. The warm white light color temperature is about 3000K, and the light color is yellowish, which can create a warm lighting environment. Therefore, it has been applied more and more in home lighting and some engineering lighting fields.

Warm white LEDs can be achieved by: (1) blue LED + yellow phosphor + nitride red phosphor; (2) blue LED + single YAG orange powder; (3) blue LED + yellow phosphor + silicate orange Phosphor; (4) blue chip + yellow phosphor + red chip. Among them, the first scheme has high color rendering index and high stability, but the overall light efficiency is relatively low and the cost is high; the second scheme has high stability and low cost, but the color rendering index is low. The third scheme has lower cost and high luminous efficiency. It is the most advantageous light effect in all schemes at this stage, but the chemical stability of the silicate phosphor itself is relatively poor, and the color rendering index is low. The fourth scheme has high light efficiency and high color rendering index, but the cost is high, and it is difficult to control the color stability. Combining the advantages and disadvantages of various technical solutions, currently, Scheme 1 and Scheme 3 have gradually become mainstream. The former is mainly used in the indoor main lighting field because of its comprehensive advantages in light efficiency and color rendering index, while the latter is in terms of light efficiency. Significant advantages, currently used in indoor auxiliary lighting or outdoor lighting .

As a mainstream application solution for warm white LEDs, there are still many problems in the application that need to be continuously improved. One of the most common problems is that in the long-term work of the light source, the light color gradually drifts, and the color temperature gradually changes from warm white to positive white. This paper analyzes the system of color-changing lamp beads in order to discover the internal mechanism of color drift and provide a reference for proposing solutions.

2. Experimental methods

In this study, a number of 5050 lamp beads with discoloration were randomly selected from a group of soft-changing flexible strips. As shown in Figure 1, the lower row of color-changing lamp beads has been compared with the above-mentioned row of undiscolored lamp beads. Significant changes have occurred, from the original orange to yellow-green.

Figure 1 The color changing lamp beads are compared with the color changing lamp beads.

Four light sources were randomly taken from the colorless and discolored light source for data testing. The test data is shown in Table 1. Comparing the two sets of data, it can be seen that the x,y value of the color of the lamp after the discoloration changes significantly, the value of x becomes smaller, and the value of y increases, the color temperature also rises from 2940K to 4300K, and the improvement of light efficiency is It is caused by an increase in color temperature.

In order to further analyze the internal mechanism of the discoloration of the lamp bead, this paper uses the energy spectrum (EDS, model _______) for the colloid of the color changing lamp bead, the silver plating in the cup, the bracket soldering foot and other parts for elemental analysis, through these parts The analysis of the elemental changes explores the mechanism of discoloration of the lamp beads.