What is UV LED?
Understand the principle of UV LED
Development of UV LEDs
UV LED (Light Emitting Diode)
In 1993, Shuji Nakamura, working at Nichia Corporation in Japan, successfully developed blue LEDs based on wide-bandgap semiconductors gallium nitride (GaN) and indium gallium nitride (InGaN) doped with nitrogen.
These LEDs became widely used in the late 1990s.
In 2001, Kafmann et al. used UV LEDs to excite trichromatic phosphors to obtain white LEDs.
It was only in the past decade that UV LEDs with germicidal capability, particularly UVC LEDs, have been gradually developed and gained commercial value. Earlier UV LEDs still operated in the longer wavelength UVA range.
Classification and characteristics of UV LED
UV LEDs are classified according to wavelength into UVA LED, UVB LED, and UVC LED.
Common UVA LED wavelengths include 340nm/365nm/375nm/385nm/395nm/405nm.
For LEDs, the wavelength can be adjusted through epitaxial growth.
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UVB LED can provide wavelengths of 295nm/310nm/325nm.
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UVC LED has wavelengths of 265nm/275nm/280nm.
Here are some points of comparison between UV LED and UV mercury lamps:
Difference between UV LED vs UV mercury lamps
1. Wavelength selectivity
UV LED has a wide range of wavelength options due to its characteristics,
while UV mercury lamps commonly come in only two wavelengths, 254nm and 365nm.
2. Switching time
UV LED can turn on and off instantly, reducing power waste when not in use.
UV mercury lamps need to preheat before use.
3. Radiant heat
UV LED is a cold light source with low radiant heat, making it suitable for curing heat-sensitive materials.
UV mercury lamps emit radiant heat, which may heat up the materials being irradiated, making them unsuitable for curing heat-sensitive materials.
4. life-time
The service life of UV LED can reach 5,000-10,000 hours,
while UV mercury lamps have a shorter lifespan, typically 1,000-3,000 hours.
5. Size
UV LED is very small, making it suitable for use in many space-restricted environments, and can be assembled in various shapes to meet different applications.
UV mercury lamps are mostly in the form of tubes and have a larger size, making them less versatile in application.
6. Structural strength
UV LED is resistant to collision and falling,
while UV mercury lamps are made of quartz tubes and are easy to break.
7. Directionality
UV LED emits light in one direction and can change the angle through different optical lenses to concentrate most of the energy where needed.
UV mercury lamps emit light in 360 degrees, resulting in a lot of wasted energy.
8. Environmental friendliness
UV LED does not contain mercury, making it the preferred choice due to its environmental friendliness.
UV mercury lamps contain mercury and will gradually be phased out due to the Minamata Convention on Mercury.
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Definition and characteristics of high power UV LED
According to the general definition in the LED industry, an LED with an input power greater than 1 watt is considered a high-power LED.
For UVA LEDs, the voltage is typically between 3.5V-4V, so an input current of 350mA or higher can be considered a high-power UVA LED.
For UVB and UVC LEDs, the voltage falls between 5V-7V, and an input current of 150mA or higher can be considered a high-power UVB/UVC LED.
According to the general definition in the LED industry, an LED with an input power greater than 1 watt is considered a high-power LED. For UVA LEDs, the voltage is typically between 3.5V-4V, so an input current of 350mA or higher can be considered a high-power UVA LED. For UVB and UVC LEDs, the voltage falls between 5V-7V, and an input current of 150mA or higher can be considered a high-power UVB/UVC LED.
When using high-power UV LEDs, heat dissipation needs to be considered. Generally, at least a heatsink is required, and in some cases, forced air cooling (fans) or liquid cooling may be necessary. Without proper heat dissipation, the LED chip temperature may rise, resulting in a shortened lifespan or even failure.
The temperature limit for LEDs is generally Tj < 120 degrees, where Tj stands for junction temperature, referring to the temperature of the LED chip. However, in practical use, to ensure good reliability of UV LEDs, it is recommended to keep the temperature below 80 degrees. Therefore, a good heat dissipation design is crucial for high-power UV LEDs, and experienced professionals are needed to design it, or thermal simulation software can be used to predict chip temperature.
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