Optical Systems for Led Lamps

 

Inside an LED, illumination emanates from a diode enclosed within a casing known as primary optics. This casing influences the light's 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 and create different effects, thus improving 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 less than 10°, therefore very narrow, up to one greater than 60°, therefore very wide.

 

IRIS

 

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 upon which it is reflected. 

 

IRIS

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 can be efficiently reflected, leading 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

Lense 

Lenses made from thermoplastic materials, with the most prevalent options being:

• PMMA (polymethyl methacrylate): This material offers high malleability during processing.
• PC/APEC (polycarbonate): Known for its impact resistance, although 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. 

Reflectors 

Reflectors for LEDs, also fabricated using thermoplastic materials, specifically:

• PC (Polycarbonate)
• PCHT (Polycarbonate High Temperature)

An additional processing step, known as metallization, is required. This step involves depositing a reflective layer onto the surface of the reflector material itself.

 

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Lens or a reflector?

It is hard 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, as well as COB LEDs. Therefore, the selection of optics is influenced only partially by the LED type. 

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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, thus some light beams will be controlled. 

For the same size with a lens, almost the entire luminous flux can be controlled, and therefore, in general, systems equipped with lens optics are more accurate than similar ones with a reflector, especially in the presence of photometric emissions at 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.