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Let’s talk about optics: the secrets of LED Lighting

17 June 2024


Egoluce explains the importance of optical systems for LED lamps


Within professional lighting systems, there is frequent discussion surrounding the secondary optics applied to LED lights, used to focus and direct light by altering its photometric distribution. Inside an LED, illumination emanates from a diode enclosed within a casing known as primary optics. This casing influences the light form, but the resulting beam tends to be broad, diminishing in intensity as it extends from the origin, rendering it less suitable for some applications.

Additional optical components are incorporated alongside the primary optics to produce more scattered or concentrated light, depending on the desired design specifications. These are necessary elements to focus light rays and maintain beam intensity while improving light distribution. In addition to directing light, secondary optics offer creative ways to play with light beams, create different effects and develop the effectiveness of a lighting system in the environment. In most cases, it is possible to find a reference regarding the optics in the product data sheets, identified with a series of values indicating the degrees of the beam angle. Commercially available are LEDs with optics starting from a value lower than 10°, therefore very narrow, up to higher than 60°, e.g. very wide.


Types of secondary optics

Secondary optics can be divided mainly into two families:

Lenses: Lenses use principles of refraction and TIR – Total Internal Reflection. A notable advantage of employing a lens is the accuracy in regulating the direction of the emitted light beam. The photometric solid distribution and light output of the system vary depending on the materials and surface treatment of the lens.

Reflectors: Reflectors utilize the principle of reflection; however, with each reflection of the light beam on the reflector surface, there is a loss due to the absorption of some of the light by the material it reflects upon. The photometric distribution primarily depends on the geometry of the reflector, its surface treatment, and the physical properties of the material coated inside it. However, this type of optical system typically exhibits lower efficiency than a lens. Not all the light emitted by the LED  efficaciously reflects. That leads to uncontrolled results.

Hybrid Systems: There are also hybrid systems that use lenses and reflectors together and systems that use diaphragms affixed to the secondary optics, which can shape the light.


Materials of optics

The lens production uses thermoplastic materials, and the most prevalent options are PMMA (polymethyl methacrylate), which offers high malleability during processing, and PC/APEC (polycarbonate) known for its impact resistance, even if it is more prone to scratches, making it suitable for products requiring high-strength properties. Silicone: Resilient to high temperatures and less susceptible to yellowing over time. The production of reflectors for LED uses thermoplastic materials, specifically PC (Polycarbonate) and PCHT (Polycarbonate High Temperature). They need an additional processing step – metallization – that involves depositing a reflective layer onto the surface of the reflector material itself.


Lens or a reflector?

It is not easy to determine a priori which type of secondary optic is superior to others because the evaluation depends on the specific application, the light source used, and the design specifications. Lenses and reflectors are manufactured for high-power and mid-power LEDs, such as COB LEDs. Therefore, the selection of optics is influenced only partially by the LED type. Secondary optics with reflectors have lower luminous efficacy than those offered by a lens because – with each bounce of the beam of the reflector surface – the reflector will absorb some of the beams, and some beams will be controlled. At the same size as a lens, you can control almost the entire luminous flux. In general, systems equipped with optics with the lens are more accurate than analogues with reflectors, especially in the presence of photometric emissions with very narrow angles (narrow beam).

Optics play a crucial role in industries and sports where regulatory requirements demand uniform illuminance. Therefore, selecting the appropriate optic is essential to ensure compliance with these regulations.

When choosing an optic, it is essential to consider both the aesthetic and functional requirements of the lighting design, ensuring the correct selection of the opening angle and optic and preventing errors that could result in insufficient lighting.



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