Optan TO-39 Ball Lens vs SMD packages: Which is right for my application?

In a spectroscopy sensor, one of the key elements in the optical design is the choice of the light source. Most organic and some inorganic compounds have their absorption peak in the UVC wavelengths. For spectroscopic measurement of these organic compounds or parameters of water or air quality, UVC LED light sources enable affordable, portable real-time measurements.

When it comes to Optan UVC LEDs, there are two options: TO-39 with ball lens, and surface mount LED (3535 package). A couple of key considerations will help decide which package is the right fit for your application.

Light Radiation Pattern

The TO-39 ball lens (BL) package has a built-in focus, with a nominal focal distance of 10 mm. For water quality and life science applications, where the path lengths are in the millimeter lengths, the ball lens package is an ideal plug and play option. For gas sensing applications, where the flow cells are much longer in the order of several centimeters, the SMD package offers customers the flexibility to design a focus capability to match the application. The other consideration would be the wider viewing angle of the SMD (130° vs 14° for the BL package).

Speed to Market vs Unit Cost

The TO-39’s built-in focus enables quicker prototyping and reduces time to market for the sensor manufacturer. The package however has a higher per unit cost compared to the SMD. In contrast, the SMD package requires an initial investment in developing the focus for the package. In addition to the lower per unit cost, the assembly costs will also be lower for the SMD package because standard PCB assembly techniques can be used in contrast to hand soldered TO-39 packages.

Drive Current

The SMD LEDs have a lower thermal resistance and hence, for the same current, experience a lower increase in the LED junction temperature. Note that LED junction temperature affects light output and lifetime. Some fluorescence applications require higher than normal light output and therefore, higher currents of operation. For these applications, the SMD could be a better fit than the TO-39 LEDs, due to the lesser increase in junction temperature.


If you have questions about Optan UVC LEDs, contact us today.

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