As the performance of UVC LEDs (short-wave UV LEDs) continues to increase, this new technology is gaining kinetic energy from life science and environmental monitoring instrumentation applications. As with all emerging technologies, designers must understand some of the fundamental differences between them and existing solutions, rather than taking it for granted that they can be “ready to use”. This allows designers to fully utilize the full benefits of UVC LEDs. After careful trade-offs, the UVCLED design reduces product size, reduces power consumption, and lowers cost of ownership for end users.

UVC LED instrumentation application

As UVCLEDs meet market demands for miniaturization, cost reduction and real-time measurement, interest in introducing them into spectroscopy applications continues to heat up. Compared to xenon or xenon flash lamps, LEDs output narrower spectral sources, and all of the component's light output can be used for measurements. Users can select specific peak wavelengths of interest based on application needs. Standardized measurement methods for 254 nm wavelength mercury lamps have been developed for specific applications. For example, when testing water and air quality in accordance with EPA standards, an LED source with a peak wavelength of approximately 254 nm is required. Table 1 summarizes some important organic compounds that can be identified by spectrum in applications such as life science research, pharmaceutical production, and environmental monitoring.

Table 1: Common organic compounds and their peak absorption wavelengths

In instrumentation applications, another major criterion for selecting a source is the light output at the peak wavelength. Since LEDs have only a single peak, the light output is concentrated at a specific wavelength, which is not the same as other ultraviolet (UV) lamps. Applications for absorption spectroscopy typically require low levels of light output - 1 mW or less. However, in the case where the flowcell is isolated from the light source, higher optical output power is required because the optical signal is severely attenuated before reaching the flow cell. This can require the LED's light output to be well over 1mW.

In the fluorescence spectral domain, the signal intensity is proportional to the intensity of the light. The excitation power of the LED depends on the level of tracer required to be detected, so in these applications, the light output required for a single LED may be greater than 2 mW. Figure 1 compares the irradiance of UV sources commonly used in instruments. Although the input power of the LED is much smaller, the irradiance in the desired UVA wavelength band is higher than other sources, making it a more efficient source of light in a particular measurement.

Figure 1: Comparison of irradiance of UVC LEDs, Xenon flash lamps and xenon lamps

After selecting the wavelength and light output, another important parameter is the viewing angle, which affects the entire optical system of the instrument. Broadly speaking, it has two options: a narrow viewing angle or a wide viewing angle. The narrow viewing angle is achieved via a ball lens and the wide viewing angle is a flat window. A narrow viewing angle provides high intensity light in a small range, while its package is typically used in applications where light is directly focused onto the instrument.

Planar windows have a wider radiation pattern and have better tolerance when used with the fiber for remote coupling. This applies in particular to applications where the flow cell must be isolated from the source and electronic circuitry (eg monitoring high temperature chemical processes or chromatographic analysis with highly volatile solvents). In practical applications: narrow-angle ball lenses minimize the number of components in the instrument; wide-angle flat windows make the design more flexible.

Optimized drive currents allow designers to balance light output and application life requirements. Driving the LED at a rated current lower than the manufacturer's specifications will reduce the light output, but will also extend the life of the source. In applications that require high LED output power, some end users choose to drive the LEDs at a higher current than the data sheet specifications. Increasing the drive current in this way increases the light output, but it also carries the risk of sacrificing performance.

Overheating is a common problem that can have a negative impact on the LED's light output and life cycle. Due to the transient switching characteristics of the LEDs, the LEDs can be turned on and off quickly in a periodic manner. In fluorescent applications where higher light output is typically required, duty cycle operations are often employed to increase LED current more safely.

The duty cycle is defined as the percentage of the LED's turn-on time in one cycle; where cycle is the total time taken to complete an LED on-off cycle. For example, LEDs that operate at 50% duty cycle have exactly half the turn-on and turn-off times. Figure 2 shows the normalized light output for different drive currents and duty cycles.

Figure 2: Here we see the effect of different duty cycles on the normalized light output, while the LED turn-on time lasts for 500 μs. The normalized power is the relative optical output power of the light output relative to the maximum rated operating current of 100 mA (with a suitable heat sink). Driving the LED with a large current affects the junction temperature of the LED, which in turn affects its lifetime and light output.

Optimized duty cycle minimizes the effects of increased drive current on junction temperature, thereby protecting LED performance. Figure 3 shows the effect of the duty cycle on maintaining the LED junction temperature. Operating the LED at 5% duty cycle increases the light output (Figure 2) by a factor of three with minimal impact on junction temperature.

Figure 3: The figure shows the effect of different duty cycles on junction temperature, where the LED turn-on time is 500μs.

Excessive heat has a negative impact on LED light output and lifetime. In the long run, heat will shorten the life of the LED. Thermal management is extremely important when using a UVCLED design because a larger portion of the energy driving the UVCLED is converted to heat than a longer wavelength LED. 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 selected PCB can also achieve better heat dissipation.

Figure 4: Comparing the thermal pad temperature of FR4 and Al PCB without heat sink (a); and the thermal pad temperature of AlPCB with and without heat sink (b)

FR4 is one of the most commonly used PCB materials due to its relatively low cost, but its thermal conductivity is low. For systems with high system thermal loads, metal core PCBs with higher thermal conductivity are a better choice. As the need for heat dissipation increases, designers often achieve better thermal management by increasing the PCB area and increasing the heat sink. If more heat is needed, designers can use more aggressive cooling techniques.

As UVC LED performance improves, designers are beginning to use their design flexibility in applications such as spectroscopic instruments and disinfection reactors. The choice of LEDs in these applications enables tighter, more efficient, and often more cost-effective designs. As UVC LED technology continues to evolve, smart designers will find more ways to take advantage of UVC LEDs to meet the challenges of these markets.

                                

Perimeter LED  Display

Outdoor Perimeter LED Display screens are basically perimeter advertising boards. They are outdoor LED displays that are used as ground level giant banner displays that are very wide in width and short in height. The perimeter LED screen boards are very commonly used for advertising and are effective in displaying continuous scrolling advertising messages on the LED displays across a sports field & at indoor sports arena. They are very quick and simple to install and they allow the module to adjust to different angles for better results on TV broadcasts. These displays are specifically used by the stadium authorities and sports clubs, sports marketing companies who can benefit from the returns they can pool in through revenue generated by advertisements during the matches. By using a super wide viewing angle, Outdoor perimeter LED display increases the amount of spectators, and also multiple advertisements can be showed at once. Also Silicon rubber mask on the LED cabinet and the top protective hat provide player & screen safety.

Priva led Perimeter LED displays can be developed in different sizes and are fitted with complete control system, power and data distribution, cables and most importantly our advertising management software. They are high refresh screens made up of completely weather-proof material suitable for outdoor applications. Our In-house team of engineers will provide you with technical support, assistance and maintenance.

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