A research team of State Key Laboratory of Ultra-precision Machining Technology (Partner Laboratory in The Hong Kong Polytechnic University) and PolyU students has developed what it believes is the most energy-efficient LED filament technology with a luminous efficacy of 129lm/W. This represents 1.5 times the efficacy of traditional LED lamps.
In 2015, PolyU Micro Fund awarded a seed fund of around $13,000 to the student team and it is expected that the product can be launched this year.
Based on the assumption of a daily operation of eight hours, a PolyU's LED filament bulb with lumen of 1300lm costs around $4 of electricity tariff per year, and contributes to 22kg of carbon dioxide emission yearly.
In comparison, a traditional LED lamp costs $6 of electricity tariff and 31kg of carbon dioxide emission yearly with the same lumen and conditions, which means that the new technology can reduce carbon dioxide emission by 30 percent.
The new technology is said to provide an expected lifetime of 50,000 hours, with only half of the production cost of traditional LED lamps.
Other advantages listed by the team include: Wide beam angle: 300degree, parallel to that of incandescent bulb; comparably high colour rendering index (CRI): Enables original colour projection of objects as if they are in natural light; less UV light emission; and more environmental friendly: absence of harmful chemicals, and consists of fewer electronic components, and 80 percent recyclable materials.
The team has taken a number of approaches to achieve these improvements.
Using Aluminium as substrate material
LED chips are sensitive to heat. Heat diminishes its luminosity and speeds up the drop of lumen, and therefore heat flow design of substrate is crucial to the lifetime of LED lamps. Instead of ceramic and sapphires, Aluminium, with good thermal conductivity, high reflectivity and affordable price, is chosen as the substrate material, to achieve longer lifetime and higher lumen at a lower cost.
Mounting low power LED chips on both sides of substrate
The larger the power (Watt) of a LED chip is, the higher the electric current it needs, leading to more energy loss. In PolyU's LED filament lamp, LED chips with large power are replaced by many tiny LED chips with small power which are mounted on both sides of the substrate. This design will reduce energy loss and generate even light diffusion, without affecting luminosity.
Applying PolyU's advanced injection moulding technology
The hemispherical plastic case of LED lamps made with traditional plastic moulding method limits beam angle. Applying advanced injection moulding technology developed by PolyU Advanced Optics Manufacturing Centre, a seamless and transparent spherical plastic case is produced to make 300-degree beam angle possible.
Enhancing power supply
PolyU LED filament lamp converts AC (alternate current) to low current DC (direct current) directly without dealing with the voltage, and hence reduces components required and simplifies circuits, enhancing reliability and efficiency of the lamp.
The patent application of this new technology has been filed and the prototype design is completed.