How to solve an LED potting problem in 24 hours

Electrolube’s Indian subsidiary recently solved an LED lighting unit potting problem, following consultations with the company’s UK-based technical division. The resin encapsulation was causing an unacceptable colour shift in the light from an LED strip luminaire, and the UK technical team had little more than 24 hours to come up with a solution.

It all started when Rockforest Technologies India was contracted to supply LED strip lighting units for luminaires destined for a shopping complex in Bangalore. The specification stipulated that Rockforest’s LED lighting strips should provide a ‘neutral white’ (4000K) colour and that the LEDs in the luminaires be potted in order to protect them from adverse environmental conditions.

Electrolube India conducted some initial trials, potting the strip luminaires to a specified depth of 5.5 mm using Electrolube’s UR5634 — a semirigid, optically clear polyurethane resin that is widely used for encapsulating LED lighting systems. With good protective and decorative properties, the UR5634 resin is also UV resistant, making it useful as an encapsulant for applications exposed to direct sunlight.

In this particular application, the resin caused a colour shift from the LED array from the specified 4000K (neutral white) to ‘cool white’ (6500K). Rockforest was under considerable pressure to solve this problem, as the 4000K colour was a non-negotiable specification; moreover, the customer requested that a new reference sample, which met the 4000K colour specification, be made available for retesting in just 24 hours.

Electrolube India General Manager Padmanabha Shaktivelu needed to act quickly to help Rockforest meet this tight deadline, so he approached Electrolube’s technical support team in the UK for advice. The UK team suggested two different approaches that Rockforest might consider in order to solve the problem.

The first of these was a recommendation that they use an LED that provided a colour temperature below the specified colour temperature — in this case, one operating in the 2500–3000K range. By potting these with the UR5634 resin to the specified 5.5 mm depth, it potentially could bring the light back to the desired colour. The second option was that Rockforest assesses the amount and type of resin they were using for this project to see if a thinner layer of resin over the top of the LED array would reduce the colour shift effect.

Shaktivelu persuaded Rockforest to switch to UR5635, Electrolube’s semirigid polyurethane resin, formulated with a hazy/cloudy appearance that is suitable for dispersing light. The diffused light produced by this resin meant that an additional diffuser medium was no longer necessary, allowing the customer to achieve the required aesthetic appearance and, through trials with various resin potting depths, the correct colour temperature. During these trials, the rapid gel time of UR5635 caused a complication, but Padmanabha solved this problem by suggesting a staged potting procedure.

“Time was not on our side when we made the discovery of the colour shift from these potted LED units,” said Bipin Rajgopal, Rockforest Technologies India’s managing director. “Our client needed a rapid solution, so we turned to Electrolube India, and Padmanabha Shaktivelu’s help was instrumental in achieving the tight turnaround demanded.

“The switch to UR5635 proving especially successful as it avoided the need for an additional diffuser medium, thereby saving costs for our client.”