Primelite Insights

What We Learned Along the Way

PrimeliteNewsInsightsMaking a Good Light Guide Choice

Making a Good Light Guide Choice

Our Light Engines are extremely potent UV-LED spot light sources, designed to provide the maximum output needed in high-power precision applications. For an efficient overall setup, additional optics or light guides used with our UV-LED light sources must meet our elevated standards. In internal tests and countless industrial applications, liquid LED Light Guides have proven to be a very reliable tool, far superior to fiber light guide alternatives.

While LED Light Guides have a numerical aperture of 0.6, the numerical aperture of fiber light guides ranges between 0.2 (standard) and 0.3 when optimized for divergent radiation. Furthermore, fiber light guides inherently have the drawback of voids between the fibers of a bundle. These dead areas cannot transmit light and make up for 30% of the light guide’s cross-section.

Compared to fiber light guide bundles, the larger aperture and a cross-section entirely functional to transmit light allow us to couple much more radiation from our LED modules into a LED Light Guide. The ability to couple more light into a light guide leads to two main advantages:

We get higher power throughput using LED Light Guides. Comparison tests between our Ø6.5 mm X 1,500 mm LED Light Guide and a Ø7.0 mm X 500 mm model (fused light entry) from a leading fiber light guide supplier have shown a 2.5 times higher output using LED Light Guides.
Due to efficient optical coupling, temperatures at the light entry are much lower. A 300-second exposure in the NUV spectral range at relatively low power settings (30%) on our Light Engine ALE/1 is enough to heat the fiber bundle’s light entry to 100°C (a rise of 70°C from the start). Our LED Light Guide stays relatively cool under these conditions, showing only a minor temperature increase. Lower temperatures of the LED Light Guide allow for long service life. Additionally, the transmission of a fiber light guide shifts by up to 5% whenever temperatures change at its entry window, which intolerably hurts the overall setup’s output stability.

Besides beneficial optical characteristics, LED Light Guides consist of a polymer tube with a liquid active core, providing better flexibility and robustness. Where fiber bundles fatigue if they are frequently bent and eventually break, our LED Light Guides are super resistant.

Conclusion

Primelite’s UV-LED light sources are designed to deliver 30 – 50 W of optical output. Using fiber light guides is no option, as no high aperture products are available. Furthermore, elevated temperatures at the light entry produce unacceptable transmission variations and cause damage to the light source in the long term. Therefore, we strongly advocate liquid LED Light Guides in combination with our equipment.