Liquid vs. Fiber Optic Light Guides for UV Curing

A light guide for ultraviolet curing is a component of the curing system that helps direct and distribute UV light efficiently to a specific area for curing or hardening of materials. In UV curing, ultraviolet light is used to initiate photochemical reactions in inks, coatings, adhesives, or resins, causing them to solidify or cure quickly.

The light guide consists of materials designed to transmit UV light effectively. Its functions are to transmit light from the spot curing unit to the area to be cured, distribute the UV evenly across a surface, and target specific areas to be cured.

When comparing liquid light guides and fiber optic light guides for ultraviolet curing, the key differences lie in their construction, performance, and specific applications. Both are used to transmit and deliver UV light, but they operate in distinct ways and have unique advantages and limitations.

Construction Factors

Liquid Light Guides: These consist of a flexible tube or conduit filled with a special liquid that transmits UV light. The liquid inside is usually a type of optical fluid with a high refractive index to guide the light. LLGs are typically more flexible than fiber optic cables, allowing for easier manipulation and the ability to bend or route around obstacles.

Fiber Optic Light Guides: Fiber optic guides are made of bundles of thin, flexible glass or plastic fibers that transmit light through total internal reflection. Fiber optics can also be very flexible but tend to be more rigid compared to liquid light guides, depending on the specific construction. They are ideal for long-distance transmission or situations where more precise control over light delivery is necessary.

Transmission Efficiency

Liquid Light Guides: Liquid guides generally offer higher transmission efficiency for UV light compared to some fiber optic cables, especially in certain wavelengths. This is because liquids can have a lower loss rate of UV energy as compared to some materials used in fiber optics. There may still be some absorption in the liquid, but they tend to perform well for specific UV wavelengths, particularly when using high-refractive-index liquids designed for optical purposes.

Fiber Optic Light Guides: Fiber optic light guides can be very efficient at transmitting UV light, especially with high-quality fibers designed for ultraviolet transmission (for example, quartz fibers). The efficiency depends heavily on the type of fiber and the coating used. Depending on the material (plastic versus quartz), fiber optic light guides can suffer from higher transmission losses, especially with longer lengths or lower-quality fibers. However, when using high-grade quartz, they can be highly efficient.

UV Light Transmission

Liquid Light Guides: They typically work well with UV light across a wide spectrum, including the deep UV (200-300 nm) range, making them ideal for curing applications that require this specific range. Liquid guides may degrade over time due to UV exposure, so the liquid inside must be specially formulated to resist UV radiation and not degrade under prolonged use.

Fiber Optic Light Guides: Fiber optic guides are typically more suitable for a narrower range of UV light. UV transmission in optical fibers may be limited by the material of the fibers (plastic fibers might not transmit UV light as efficiently as quartz fibers). Fiber optic cables, especially those made from quartz, have better resistance to UV degradation than liquid guides. They are durable and capable of withstanding prolonged exposure to UV light without degradation.

Size and Shape

Liquid Light Guides: LLGs are often available in larger diameters and can be more flexible in terms of shape, making them better for larger-area curing or for areas with complex geometries. They can be customized for larger or more irregularly shaped curing zones, as the liquid inside can easily be distributed in various forms. For instance, the liquid light guides we offer range from 5mm in diameter to 8mm, and are up to 3 meters in length.

Fiber Optic Light Guides: Fiber optics can be produced in a range of diameters but are generally available in smaller sizes. They are ideal for delivering UV light to small or precisely defined areas. Fiber optics are often bundled into cables, so they can be manipulated to a certain extent but are less flexible in their ability to cover a large or highly irregular area compared to liquid light guides. For the ones we offer, the diameters are as small as 1.77mm, with a max length of only 1.5 meters.

Durability and Maintenance

Liquid Light Guides: Liquid light guides are more prone to wear and tear, especially if the liquid is exposed to prolonged UV radiation or high temperatures, which could cause it to degrade over time. These guides may require maintenance, such as refilling or replacing the liquid, which can be more involved than replacing a fiber optic cable.

Fiber Optic Light Guides: Fiber optic guides, especially those made from quartz, are highly durable and can withstand harsh environments, including exposure to UV light. They typically have a longer lifespan than liquid guides. Fiber optics generally require less maintenance compared to liquid guides. If a fiber optic cable gets damaged or broken, it can be replaced more easily than liquid light guides, which may require more intensive repairs.

Cost

Liquid Light Guides: Liquid guides are generally less expensive to manufacture than high-end fiber optic cables, especially when using flexible plastic tubing and less specialized liquids. They can be significantly less expensive than fiber optic cables.

Fiber Optic Light Guides: Fiber optic light guides, especially those made from high-grade quartz, tend to be more expensive, but they offer better long-term durability, efficiency, and resistance to UV degradation, which may justify the higher upfront cost. For some applications, the smaller size may be essential, making them the only option.

Bottom Line

In the most popular sizes for light guides, both liquid and fiber optic options are available. This means that, due to the much lower cost of LLGs, they are more commonly used and are often the default light guide that is offered with a spot curing system.

However, for special applications, fiber optic light guides come in smaller diameters that might be critical for curing of small areas, despite their noticeably higher cost. And their longer life may also justify the initial investment.

Light guides for ultraviolet curing are offered in a wide variety of sizes and lengths, and we did not even have time in this article to examine bifurcated, trifurcated, or quad guides, which also serve various important functions. Finally, there are even a small number of LED light guides now on the market, usually used in very specialized equipment.