Solutions to improve LED light quality and light efficiency

Light quality The light quality we usually talk about mainly refers to light distribution, light angle and shadow, and color rendering. Here, Zhou Xuejun particularly emphasized that designers should pay attention to: Is the light color of different LED particles consistent? Is the change of different particles consistent over time? Is there a color difference of an LED at different angles? How is the color rendering index?

The entire LED packaging process includes two important steps: bonding the chip and pins with gold wires, and applying phosphors. Both steps will cause color difference in the LED, especially the gold wire will block the light path. If the operation is not done properly, it may cause hidden cracks in the chip, thus forming a risk of chip breakage.

In order to solve these problems, Philips Lumileds' latest LUXEON Rebel LED series uses the latest TFFC (thin film flip chip technology) and unique Lumiramic phosphor technology.

According to Zhou Xuejun, the electrodes of TFFC technology are behind the circuit board, and there is no vertical or horizontal wiring on the surface, so the physical structure is better. Lumiramic phosphor technology uses ceramic phosphor plates instead of phosphors to directly bond to the chip, making the surface completely flat without bumps and unevenness. Therefore, it fundamentally avoids the color inconsistency of most LEDs at angles off the central visual axis caused by uneven phosphor coating in traditional packaging methods. "In addition, the use of Lumiramic technology can also reduce the range of white light binning to 1/4 of the original," Zhou Xuejun added.

At present, the most troublesome problem for the lighting industry, especially lighting design, is binning. For some experienced LED manufacturers, the common practice is to use the entire output range of white light LEDs in all bins. However, at a specific CCT (correlated color temperature), it is impossible to produce white light LEDs with high consistency at low cost. The main reason is the wavelength of blue light LED chips and the coating process of phosphors. Therefore, manufacturers may mix and use multiple binned LEDs, but in this way, the application range of the product is limited, which not only increases the complexity of the production process, but also generates more inventory. Cree's solution to this is EasyWhitebin, which uses Cree's multi-chip XLampMC-ELED. The MC-E chip is packaged in four cores. Cree selects four white light LED chips with different characteristics (covered with phosphors) and packages them. The mixed white light output can achieve the expected color temperature and is far less than the standard range specified by ANSI.

The performance of luminous efficiency is like Moore's Law in the semiconductor industry. The LED industry also has a Haitz's Law, which states that LED brightness doubles approximately every 18-24 months. In the next 10 years, it is expected that the brightness can be increased by another 20 times, and the cost will drop to 1/10 of the current level. Today, 1 US dollar can buy about 100-150 lumens on the market, and the US Department of Energy predicts that this number will reach 1,000 lumens in 2020.

How to improve the luminous efficiency of LED? First of all, let's look at the packaging. At present, the most common LED light sources on the market are direct plug-in and surface mount. Zhu Xiaotian, deputy technical director of Shenzhen Changguang Semiconductor Lighting Technology Co., Ltd., believes that the cross-sectional area of ​​the heat dissipation outlet of these two packaging methods is small, and the primary light outlet channel is narrow, and the utilization rate is relatively low. According to the light emission characteristics of LED, Changguang Semiconductor designed a flattened primary optical channel to form a planar light source array chip, which can minimize optical loss. In this regard, Zhu Xiaotian explained: "Like SMD's 3528 or 505 light sources, glass fiber or plastic is used as the substrate, and the bottom is not connected to any metal. The planar light source array chip adopts the direct packaging technology based on multi-chip integrated COB. The aluminum substrate used by the light source can dissipate more heat through direct heat dissipation." It is reported that the company currently has completely independent intellectual property rights for LED surface light source technology. The light efficiency has reached 130lm/w, and the overall light efficiency is greater than 100lm/w.