As the performance of UVC leds (short-wave uv leds) continues to improve, the new technology is gaining kinetic energy from the use of life sciences and environmental monitoring instruments. As with all emerging technologies, designers must be aware of some fundamental differences from existing solutions, rather than taking it for granted that they can be switched. This allows the designer to take full advantage of UVC leds. With careful tradeoffs, uvversions can be designed to shrink product sizes, reduce power consumption, and reduce cost of ownership for end users.
Instrument control application of UVC LED
As UVCLED meets market demands for miniaturization, cost reduction and real-time measurement, interest in importing it into spectrum applications continues to grow. Compared to deuterium or xenon flash, LED output of a narrower spectrum light source, the light output of the element can all be used for measurement. The user can select the specific peak wavelength of interest according to the application requirements. For specific applications, a standardized measurement method of 254nm mercury lamp has been developed. For example, when water and air quality is tested according to EPA standards, an LED light source close to the peak wavelength of 254nm is required. Table 1 summarizes some important organic compounds that can be identified by spectrum in the applications of life science research, drug production and environmental monitoring.
In the application of instrument control, the other main criterion of choosing the light source is the peak wavelength light output. Since leds only have a single peak, their output is concentrated at a particular wavelength, unlike other ultraviolet (UV) lights. The application of absorption spectrum usually requires a lower level of light output - 1mW or less. However, in the case of flowcell isolation from the light source, higher optical output power is required because the light signal is severely attenuated before reaching the flowcell. This can require LED light output far more than 1mW.
In the fluorescence spectrum, the signal intensity is directly proportional to the intensity of light. The excitation power of the LED depends on the level of tracer concentration to be detected, so the light output required for a single LED may be greater than 2mW in these applications. Figure 1 compares the irradiance of UV light sources commonly used in the instrument. Although the input power of the LED is much smaller, the irradiance in the required UVA wavelength section is higher than that of other light sources, making it a more efficient light source for specific measurements.
Another important parameter after selecting the wavelength and optical output is the Angle of view, which affects the whole optical system of the instrument. Broadly speaking, it has two options: a narrow view or a wide view. The narrow Angle of view is realized by spherical lens, while the wide Angle of view is plane window. A narrow viewing Angle can be used to obtain high intensity light within a small range, and its encapsulation is usually used for direct light focus projection onto the instrument.
The plane window has a wider radiation pattern and a better tolerance when used with the optical fiber for remote coupling. This is particularly suitable for applications where the circulation pool must be isolated from light sources and electronic circuits (such as monitoring high temperature chemical processes or chromatographic analysis with highly volatile solvents). In practical application, the narrow Angle lens can minimize the number of elements in the instrument; And wide Angle plane window makes the design has flexibility more.
Optimizes the drive current so that the design engineer can balance the light output and the service life of the application. Driving an LED with rated current below the manufacturer's specification will reduce the output of light, but will also extend the life of the light source. In applications where high LED output power is required, some end users choose current driven leds that are higher than the data table specifications. Increasing the drive current in this way increases the output of light, but also carries the risk of sacrificing performance.
Overheating is a common problem that can negatively affect both LED light output and life cycle. The LED can be turned on and off rapidly in a periodic manner due to its transient switching characteristics. In fluorescent applications that generally require more high-light output, the dutycycle operation is often used to increase the LED current more safely.
The working cycle is defined as the percentage of LED opening time in one cycle. The period refers to the total time used to complete an LED on-off cycle. For example, leds that work in 50% of the work cycle have exactly half the opening and closing times. Figure 2 shows the normalized optical output of different driving currents and working cycles.
At the same time, the LED continues to open at 500 seats. The standardized power is the relative output power of light when the maximum rated working current is 100mA (with proper radiator). Driving LED with large current will affect the LED junction temperature, and further affect its service life and light output.
The optimized working cycle can minimize the impact of increased drive current on junction temperature, thereby protecting LED performance. Figure 3 shows the possible impact of the work cycle on maintaining the LED junction temperature. By operating the LED at 5% of the working cycle, the light output (figure 2) can be increased threefold when the effect on the junction temperature is minimal.
Excessive heating has negative effects on LED light output and service life. In the long run, heating shortens the life of the LED. Thermal control is extremely important when UVCLED is designed, as much of the energy driven by UVCLED is converted into heat compared to longer leds. Proper thermal management can keep the junction temperature below the requirements of a particular application and maintain the performance of the LED. In addition to passive and active cooling methods, the PCB selected can achieve better heat dissipation.
Because of its relatively low cost, FR4 is one of the most commonly used PCB materials, but its thermal conductivity is low. For systems with high thermal load, metal core PCB with higher thermal conductivity is a better choice. As the demand for heat dissipation increases, designers often achieve better thermal management by increasing PCB area and heat sink. If greater heat dissipation is required, the designers can also adopt more aggressive cooling techniques.
With the improvement of UVC LED performance, designers began to apply the advantages of flexible design to spectrum instruments and disinfection reactors. Using leds in these applications allows for a tighter, more efficient and often more cost-effective design. As UVC LED technology continues to evolve, smart designers will find more ways to leverage UVC LED strengths to meet these market challenges.