Pratibha Sharma and Saya Han
An effort to phase out mercury-based lamps and deploy energy-efficient UV light sources is driving considerable growth in the UV LED market.1 UV LEDs are currently utilized in many single-chip or low-power applications such as point-of-use water treatment devices, sensors, and portable disinfection units. However, continued technological advancements have allowed for increased implementation in high-intensity and high-dosage applications. Improvements in UV LED efficiencies and lifetimes, particularly in the UVC range, are driving the way for the development of large systems.
The demand for such arrays arises from the need to deliver high optical power in compact, energy-efficient, application-specific systems. Unlike traditional UV lamps, which lack the design flexibility needed for system integration, high-density UV LED arrays offer superior irradiance per unit area, better spectral control, and precise positioning in a scalable format. These capabilities are essential for advanced applications including photolithography, UV curing, spectroscopy, and medical devices, where system performance, uniformity, and control are paramount. With the UV LED market anticipated to grow at a compound annual growth rate of 21.5% from 2023 to 2030,2 high-density UV LED arrays are increasingly replacing incumbent technologies to meet the needs of next-generation applications.
High-density UV LED arrays provide great flexibility to system designers in delivering concentrated light homogenously to target areas.3 While commonly available, surface-mount device products may be arranged in arrays to deliver the required flux; in many cases the LED density must be increased to achieve target irradiance levels. For these applications, chip-on-board (COB) designs are often utilized to reduce the spacing between each LED chip and increase the overall irradiance. High-density array development becomes a necessity for applications requiring multi-wavelength sources or for achieving varying beam profiles from a single source.
Several factors must be kept in mind when customizing and designing a high-density UV LED array. Some factors include:
1. Binning considerations: Binning constraints in high-density UV LED arrays arise from the need to maintain uniformity in optical power, wavelength, and forward voltage in closely packed arrays. Forward voltage differences can lead to uneven current distribution, accelerating degradation in certain LEDs. However, binning restrictions can require multiple production rounds due to the reduced yield of specified ranks. These factors necessitate careful trade-offs between binning precision, manufacturing efficiency, and array performance stability.
Voltage constraints: Voltage across LED arrays (connected across series or parallel connections) is typically limited to 60 VDC to avoid hazards. This implies that a large UV array may have to be fragmented into several arrays with its own independent circuits.
Current constraints: When connecting LEDs in parallel, the maximum current in a product datasheet should never be exceeded to ensure LED reliability and lifetimes. LEDs are current-driven devices and can be operated at constant current or using pulse-width-modulated techniques, the latter of which requires consideration of LED rise and fall times when selecting duty cycles/frequency.
2. Junction Temperature control: Junction temperature is a key factor in achieving target optical outputs4 not only at the beginning of operation but also over the target lifetimes (L70). Figure 1 shows the decrease in optical output with junction temperature at different driving currents for a 385-nm LED.
The effect of excessive heat may be more pronounced for high-density arrays if the thermal solution is not optimized accordingly. Thermistors may be mounted on the board to ensure that the temperature levels are always within range.
3. Optical Design: LEDs typically emit at an emission angle of 130 to 140 deg. Such angles may not be suitable to direct light to targeted areas efficiently. As a result, there is a need to utilize additional optics for many applications. There are several considerations when an optic is to be selected for the UV range:
Material transmittance: Standard lighting materials are unsuitable for UV LEDs, as common glass lacks UV transparency. Even UV-transparent materials can degrade over time. For UVC wavelengths, quartz or fused silica are preferred due to their high transmittance and durability.
LED Spacing: In high-density UV LED arrays, LED spacing is influenced by the size and mounting method of lenses or reflectors, which are typically attached using adhesives or mechanical fixtures. These components can limit how closely LEDs can be packed, reducing array density and potentially causing non-uniform irradiance distribution across the target area. Additionally, the reliability of adhesive bonds under UV exposure is critical, as degradation can affect optical alignment and long-term system stability.
Use of reflective materials: Depending on the wavelength of interest, reflective materials such as aluminum or PTFE may be utilized in the system (or in an optical component such as a reflector) to improve target irradiances.5
Design of optics: Optical components like aspheric, TIR, and Fresnel lenses are used to control beam angles and concentrate light, with options ranging from ~10 to 120 deg.
Custom-designed UV LED arrays may even employ a variety of optics within the same array to achieve greater control of the target irradiance and uniformity. In high-density, compact UV LED arrays, flat windows or lenses may be preferred over individual optics to maintain compactness, making precision manufacturing essential for consistent performance. Optical simulation allows for cost-effective optimization of such arrays and is a proven method for selecting optical components. Figure 2 includes an example optical simulation of an LED array with lensed 265-nm LEDs.
High-density LED arrays require carefully selected power supply units (PSUs) to ensure reliable operation, uniform output, and thermal stability. Mismatched PSUs can lead to non-homogenous irradiance distribution, overheating, or even system failure. Accurate matching of voltage and current of the PSU to the specific array configuration is essential, especially if LEDs of different electrical characteristics are placed on the same board. Multiple PSUs may be required if the size of the array is large.
In addition to the voltage and current values, PSU efficiency must also be looked at to reduce power loss and heat buildup, critical in dense layouts where thermal load is already high. Off-the-shelf PSUs typically have embedded overvoltage protection systems, but for sensitive systems, additional external snubber circuits may help suppress voltage transients and protect components. Commercial PSUs often support analog or resistive dimming (e.g., 0-10-V), as well as pulse-width modulation control. This can provide an added layer of granularity in intensity required for certain specific applications. The energy consumption may also be reduced by using a combination of duty cycles and frequencies, depending on the application. Furthermore, PSU certification (UL, CSA, etc.) may be essential for compliance with safety standards, especially in regulated industries like medical device manufacturing.
Thermal management plays a crucial role in lowering LED junction temperatures.6 High junction temperatures can reduce light output and shorten LED lifetimes. While off-the-shelf thermal solutions may still be suitable for high-density arrays, most custom arrays necessitate tailored thermal approaches to effectively dissipate heat. Minimizing the overall thermal resistance and enhancing heat extraction are the primary roles played by thermal management solutions applied at different stages in the system to dissipate maximum heat effectively.
In terms of packaging, a COB architecture inherently offers superior thermal performance for high-density arrays by eliminating individual LED packages and mounting bare dies directly onto a thermally conductive substrate. This direct interface significantly reduces thermal resistance and enables efficient heat extraction across the entire array. In high-density configurations, where thermal load is concentrated, a COB’s integrated thermal path is a key advantage ensuring better junction temperature control, higher drive current capacity, and longer operational lifetime. The addition of electrically isolated thermal pads in the LED package itself can further reduce the thermal resistance and create a direct path to dissipate heat effectively. Figure 3 includes examples of two high-density UV LED arrays.
Regarding substrates, for high-density LED arrays, metal-core PCBs offer enhanced thermal conductivity allowing to effectively dissipate concentrated heat generated by densely packed emitters. Incorporating thicker copper layers and optimized thermal vias further improves heat spreading and extraction from the active region, helping to maintain lower junction temperatures and ensuring consistent performance across the array.
High-density LED arrays generate significant thermal loads in compact footprints, requiring advanced cooling strategies beyond passive cooling. While heatsinks with thermal interface materials are sufficient for smaller arrays, high-density systems often rely on active cooling, such as fans or blowers, to maintain safe operating temperatures within smaller form factors. For even higher thermal demands, liquid cooling with pumped systems or cold plates provides a scalable and efficient solution. When implementing cold plate designs, careful consideration must be given to material choice, size, channel flow path, and the positioning of inlets and outlets, along with the appropriate chiller selection to ensure consistent thermal performance. Figure 4 lists various methods which can be used to extract heat from LED arrays at each stage in manufacturing.
Thermal simulations provide a budget-friendly, accurate, and time-saving method for developing optimal thermal management strategies.
High-density UV LED arrays are rapidly emerging as viable and often superior replacements for traditional UV lamps. By taking an integrated design approach and carefully balancing optical output, electrical drive conditions, and thermal management, engineers can unlock the full potential of UV LEDs in compact, efficient, and application-specific systems. Compared to legacy lamp technologies, these arrays offer improved energy efficiency, longer lifetimes, faster response times, and greater flexibility in wavelength and form factor. As the technology continues to mature, well-designed high-density UV LED systems are not just alternatives, they are the next standard in precision UV illumination across industrial, medical, and scientific domains.
the authors | Pratibha Sharma is the director of Applications Research and Development at Violumas/Cofan Thermal.
Saya Han is the director of Business Development at Violumas, Inc., specializing in managing projects for high-power, industrial UV applications.
1 Yoshihiko Muramoto, Masahiro Kimura, and Suguru Nouda, “Development and future of ultraviolet light-emitting diodes: UV-LED will replace the UV lamp,” Semiconductor Science and Technology, vol. 29, no. 8, June 2014.
2 Coherent Market Insights, “UV LED Market worth US$3,708.0 million by 2030, at a CAGR of 21.5%, says Coherent Market Insights,” Dec. 21, 2023.
3 Pratibha Sharma et al., “Design Considerations for a Surface Disinfection Device Using Ultraviolet-C Light-Emitting Diodes,” Journal of Research of NIST, Feb. 16, 2022.
4 Pablo Fredes et al., “Empirical and Theoretical study of the Thermal Performance of High Power UVC LEDs,” in Proceedings: Optica Advanced Photonics Congress 2022, Technical Digest Series, Optica Publishing Group, 2022.
5 Pawel de Sternberg Stojalowski and Jonathan Fairfoull, “Comparison of reflective properties of materials exposed to ultraviolet-C radiation,” Journal of Research of the National Institute of Standards and Technology, vol. 126, 2021.
6 Clemens JM Lasance and András Poppe, Thermal Management for LED Applications, Springer: New York, NY, 2014.