Light-Curing Technology Series — Light Source 1

A key component of photopolymerization technology is the light source. From the perspective of photoinitiators, the light sources required for photopolymerization can be categorized into… Ultraviolet (UV) light source and Visible light source 。

1. Visible light source

At present, its applications in photopolymerization technology are relatively limited; the most common use is as a photoinitiator in the dental restoration industry, where visible light poses comparatively less harm to humans, with camphorquinone (CQ)—which exhibits good biocompatibility—being the predominant component.

2. Ultraviolet (UV) light source

Ultraviolet (UV) light sources are the most widely used in photopolymerization technologies. At present, there are numerous ways to generate UV light, which can be categorized according to specific application requirements as follows: Medium-pressure mercury lamps, electrodeless lamps, metal-halide lamps, low-pressure mercury lamps, excimer lamps, lasers, and UV   LED light Wait.

3. Medium-pressure mercury lamp

Medium-pressure mercury lamps are currently the most common ultraviolet light sources, with applications primarily in coatings (for wood, plastics, metals, paper, etc.), inks (offset, screen, flexographic, and others), adhesives, and composite materials. These lamps typically have a service life of around 800 to 1,000 hours, are easy to disassemble, and have relatively low costs; however, they also suffer from drawbacks such as significant heat generation, ozone production, high energy consumption, and mercury contamination.

4. Electrodeless lamp

The most significant difference between an electrodeless lamp and a medium-pressure mercury lamp is the absence of electrodes. Their light‑emission mechanisms are identical: both rely on the release of ultraviolet radiation as mercury atoms transition from an excited state to the ground state. In a medium-pressure mercury lamp, this excitation is achieved via an electric arc, whereas in an electrodeless lamp, it is induced by microwave energy. Compared with medium-pressure mercury lamps, electrodeless lamps offer a longer service life and faster start-up times.

5. Metal halide lamp

Metal halide lamp A derivative of mercury lamps, these lamps incorporate trace amounts of metal halides into the discharge tube to modify the emission spectrum, selectively enhancing specific wavelengths—examples include common iron‑doped and gallium‑doped lamps. Metal‑halide lamps are particularly suited for applications requiring deep curing of coatings and other formulated products, such as white furniture finishes.

6. Low-pressure mercury lamp

Low-pressure mercury lamp The primary wavelengths are 185 nm and 254 nm, with 254 nm being the dominant one. A common application is disinfection; however, compared to medium-pressure mercury lamps, low-pressure mercury lamps have drawbacks such as lower power, shorter wavelengths, and poorer penetration. Precisely because low-pressure mercury lamps emit ultraviolet light at relatively short wavelengths, they are often used in photopolymerization technologies to achieve special effects, such as snowflake finishes and a soft, matte texture.

7. Excimer lamp

Excimer lamp Its operating principle involves exciting certain materials—such as xenon or krypton—to form excited dimers (excimers). As these excimers decay back to their ground state, they emit ultraviolet light at specific wavelengths. Xenon emits light at 172 nm, krypton chloride at 222 nm, and xenon chloride at 308 nm. Excimer lamps are also instant‑on, boast a long service life, and are commonly used in photopolymerization technologies to produce matte, skin‑friendly coatings.

8. Laser

Crystalline materials can tune light sources to specific wavelengths, and lasers generate light at particular wavelengths through nonlinear processes in these materials. Several types of lasers have already been employed in optical imaging and in the fabrication of microcircuits on silicon wafers. Currently, 355-nm lasers are widely used in industrial 3D printers.

9. UV   LED

As the most promising technology to replace the currently dominant mercury‑lamp light sources, it will be discussed in detail in the next related article.