The wavelength below 380nm belongs to invisible light, the following picture shows the lamp band of 365nm in the specification 3535 series, theoretically the electric energy would be all converted into ultraviolet and with a certain amount of heat. However many times we can see purple and blue light, that is because the chip also converts some of the electricity into visible light.
One application, the UV-LED light source has used as a radiation source to realize the curing of the UV Curing Material, the traditional one used in this field is a medium high-pressure mercury lamp, but it can cause pollution problem, considering the environmental protection factors, the UV-LED light source manufactured by using the semiconductor light-emitting principle was widely used and developed this years.
The Principle of UV-LED Light Curing
Before learning the working principle of light curing, it is necessary to understand the principle of LED luminous. According to the principle of electron transition, the electrons of atoms return from excited state to ground state, and at the same time the corresponding light source will be emitted by radiation of different wavelengths. Photoinitiator needs to be excited by absorbing the energy released by LED to make the UV curing material totally curing. And study shows the UV led’s energy can meet with it.
Present Situation of UV-LED
The shorter the wavelength of LED and the higher the energy level, the higher the price. The lower the energy needed for photoinitiator excitation, the longer the absorption wavelength, the higher the price. Those two parts contain each other's cost, so it is one of the research directions of the enterprise to find the best balance point between them to control the cost.
The industrial chain of LED itself is very complex, from crystal production, chip cutting, to chip packaging, to the integration of light source module, also involves the control of power supply and the design of heat dissipation system and so on. Each step has a very important impact on the quality of the final product. Those are the cost where come from.
The emission spectra of LED are narrow, and the peaks of 365nm and 395nm (including 385nm-405nm) are common. At present, the curing of UV materials is mainly UVA near ultraviolet light, mainly 365nm and 395nm wavelengths. In the process of light curing, three main parameters should be considered, wavelength, light intensity and total-work. The wavelength determines whether the photoinitiator can be excited, the light intensity determines the initiation efficiency of ultraviolet light, and directly affects the result of surface drying (antioxidant polymerization) and deep curing, while the total work determines whether the curing can be carried out thoroughly.
Emission spectra of mercury lamps and UV LED
From the diagram, compared with mercury lamp, LED has the greatest advantage that the wavelength of led is formulated and adjustable. Within the range of LED's own ability, it can be adjusted with the formula to the greatest extent according to the needs of curing. In the light curing experiment of UV-LED, the direction of enterprise’s efforts is to expand their ability boundaries and find a balance point. According to the formula of coating, to find the light source parameters of LED needed to realize the best curing.
Emission Wavelength of Led Chip with Different Material Ratio
From the diagram, theoretically, what wavelength of light can be realized by the ratio of luminous materials, restricted by various conditions, the types of UV LED chips that can be commercialized are still very limited. The high power chip for industrial application is basically concentrated in the UVA band of 365nm-415nm.
The luminous of LED is all-wave, in order to achieve higher effective optical efficiency (positive light efficiency), scientific and reasonable optical design is also needed. For instance, some products take reflection cup. Led light source is lamp bead structure, which can adjust length, width, irradiation angle and so on according to the need to make point light source, line light source, surface light source to meet the requirements of different irradiation technology.
In addition, because of the high photo-decay rate of ultraviolet light in the medium, many assessments should be carried out on the material selection of the lens (quartz glass, high borosilicate glass, toughened glass, etc.). Try to choose the material with high UV transmittance, but also to avoid the temperature rise when the material absorbs light for a long time. High temperature will destroy the chip to reduce the life.
According to the principle of energy conservation, while electric energy is converted into light energy, a large part is also converted into heat energy (UVA band, electricity: light: heat = 10:3:7). The effective service life of led chip is closely related to the temperature saving, in the process of light curing, In order to provide higher optical power density, it is often necessary to integrate the high density of led chip, which puts forward high requirements for heat dissipation, how to achieve efficient heat dissipation and to ensure that the temperature saving of all led chips is in a reasonable and balanced range. Scientific design, computer simulation and practical testing are also needed.
All these technologies have greatly influence on the production of LED and need to be perfected step by step. We believe that the application in this area will have a clear future.
HongKong Double Light Electronics Technology Co., Ltd
Address:4005, Floor 40th, Saige Square, Huaqiang North Road NO.1002, Futian District, Shenzhen City, Guangdong Province China,
Tel: (+86) 755 82853859
Fax: (+86) 755 83229774
Contact Person: Mr. Rony Qiu