ROLE OF OPTICS IN LED LIGHTS

The optics in any LED lighting system is crucial elements of that system’s performance, as they alter the directionality and intensity of light from the LED source. Optics in LED lighting can include the spatial distribution of light from the diode itself, and the reflectors, lenses, and holders that cut off or limit output light with mechanical blocking devices. Facilities that install LED lighting systems will use different optics in LED lighting, for example, to control the beam angle of the output light, to create either crisp-edged or diffused light, or to concentrate light in certain areas while limiting it in others.

LEDs are directional lighting, illuminating only 180 degrees. This is attributed to the design of an LED, as you can see below, a light emitting diode consists of one or more die, mounted on a heat-conducting material, with the primary optic enclosing the die. Therefore, the maximum angle LEDs can emit is 180 degrees as the substrate is on the back side of the die. 

The primary optics of an LED is a little protective dome. And it’s usually over the diode. The optics serves to protect diode  and shape the output of the small diode. 

Along the center axis, the LED emits 100% of its relative luminous intensity and will lose intensity the farther away you move from the center. It is obvious when you are losing light output over the spectrum, that a secondary lens or optic is needed to intensify that light and use the brightness and efficiency of LEDs to their full capacity.The light from the LEDs primary optic is still too broad for most applications, lacking intensity over distance. This is why most LED fixtures use secondary optics.

To alter the beam of light coming from the LED source, lighting fixtures require at least some type of secondary optics. The secondary LED optics takes all the light within a given bulb or fixture, and magnifies the intensity towards the target, based on how the optics is designed. Secondary optics is not only made to collimate the light, but is sometimes also used to improve color uniformity and light distribution within the targeted area.

There are four types of secondary LED optics—lenses, reflectors, TIR (total internal reflector) optics and TRIMS. 

LENSES

Lenses come in different materials, like polymethyl methacrylate (PMMA), also known as acrylic, polycarbonate, silicone plastic, and polybutylene terephthalate (PBT). Most lenses use optical grade PMMA and achieve a lighting efficiency of 90%. Optical grade PMMA lens material is harder and more fragile compared to polycarbonate and allows for the use of high current and high-temperature conditions. Apart from PMMA, polycarbonate material also offers excellent optical characteristics.

Various properties of LED lenses enable the desired lighting effect and precise control over the beams of light. They come in various shapes and sizes—for example, round, square and hexagonal. The lens directs light from the centre of the source to the reflector

Aside from altering the angle of the light being emitted from the LED and therefore altering the beam angle, the lens is generally of two types:

Clear lens which creates a distinct spot light effect good for impact ‘accent’ lighting in fashion outlets, jewellers, etc., but can create glare so correct placement is important, generally only used in commercial applications. 

Opaque lens or Fresnel lens which acts as a diffuser to soften the light for general ‘ambient’ type lighting for residential and general commercial lighting applications where glare needs to be reduced.

The limitation of the opaque or Fresnel lens is that there is a reduction in lumens depending on the opacity and quality of the lens. The Fresnel lens can also have the effect of scattering the light such that narrower beam angles can seem slighting wider, for example a 45° LED light bulb with a Fresnel lens appears more similar to a 60° LED light bulb with normal opaque lens.

When lenses get exposed to heat and light, the materials used degrades over time. The lenses become yellow, leading to color shift, and due to this, the performance will vary between two luminaries.

REFLECTORS

LED reflectors are smooth, multifaceted inside, and come in different shapes. This enables them to create a range of lighting effects. They collect and disperse the light depending on their shape. Some reflectors contain a sub-lens, for additional control of the light. A typical reflector comprises a polycarbonate moulding with a metallised reflective coating. The metallised surfaces can achieve high reflectance, although a lens ensures superior beam control. In terms of cost and ease of manufacturing, reflectors are hard to beat but they offer less control than LED lenses.

The use of a reflector can also allow the elimination of the lens to reduce the losses. 

The downside to reflectors is that the vast majority of light rays coming from the central emitter pass through the LED light source without even hitting the reflector. This means that a good portion of the light will stray wide off the intended target, creating glare, and this is where TIR optics is required.

TOTALLY INTERNAL REFLECTOR (TIR)

Designed around the phenomenon where light travelling from one medium to another of lesser optical density hits the interface at an angle and reflects with 100% of the beam energy, TIR optics, or TIR lenses, consist of a refractive lens nestled inside a reflector and are typically cone-shaped with optical efficiencies as high as 92%. The lens directs light from the source’s centre to the reflector, which sends it out in a controlled beam. An additional surface over the assembly provides another opportunity to modify the light.

TIR optics is able to utilize the characteristics that are unique to LED.

Unlike incandescent, who radiate heat outward, LEDs send heat out their base, allowing TIR optics to fit tightly over the top. TIR optics has proved prevalent in the outdoor and heavy duty space, but hasn’t gained traction in forward projection applications. Optics has an amazing ability to extract and control all of the light produced by solid state lighting.

The fundamental working principle is same for both TIR lenses and reflectors, but the TIR lenses enjoy greater control over light. With reflectors, a large amount of light doesn’t touch the reflector, and this light can’t be controlled in any way. Reflectors can be easily implemented and cheaper to manufacture than TIR optics, but the reflectors’ efficiency is clearly lower, compared to TIR optics. A TIR lens manages both direct and reflected light, whereas a reflector manages reflected light but leaves the direct light unmanaged.

The TIR lens collimates the LED light into efficient, well-controlled light beams that maximize the usable lumens in the target area with an absence of discomfort glare or shadows. The result is a smooth, high quality beam of superior intensity and uniformity, suitable for downlighting and directional lighting applications. The narrow beam options are excellent for throw or distance lighting, adding punch to Stage and Entertainment applications.

LIGHTING TRIM

In recessed lighting fixture, the TRIM is the only component that we see with the naked eye. The rest of the recessed lighting fixture is concealed behind your ceiling.

Trim refers to the light exit assembly that provides optical regulation and aesthetical enhancement for a recessed downlight. The light exit assembly is designed to maximize delivered lumens, shape the radiation pattern of LEDs, conceal the LEDs from direct view, and seal the ceiling cut out for seamless architectural integration.

The trim rests inside of the housing and just out to form the outer ring, or moulding, of the lighting fixture. 

It covers the point where the ceiling joins the downlight to create a smooth and stylish transition between surface and light, being not only decorative but functional

Some types of trim include a fixture that can be adjusted to shine directly on different areas of a room. Others have a protective outer cover.

Recessed lighting trims serve three purposes:

• Ø  They conceal the recessed fixture behind them.
• Ø  They direct and shape the light downward.
• Ø  They provide a finished/decorative look.

Types of trims to use for various types of recessed lighting are as below:

Baffle trim:

Baffle trims are the most common type of trim available for recessed lighting. This is cone-shaped and made of metal.  This type of recessed light has grooves set into it, which are meant to block excess light.

This reduces glare and shadows, so we can choose this type for a pure and soft ambient light. It reduces eye strain, being pretty comfortable and healthy. Due to the soft, gentle light it produces, baffle trim is also popular in home office settings.

Black baffles can reduce the glare further.      

The fixtures are suitable for task illumination, facilitating reading or sewing, also for bedrooms, studies, nurseries. When you read or work on your PC, smooth, flicker-free illumination is healthy. It reduces fatigue and eye strain.

If the ceiling in your living room is low, it might be a suitable option too.

Reflector trim:

A reflector trim comes with smooth, polished-metal interior. They make it easy to direct the lamps’ full output to certain areas. These fixtures maximize brightness. So, they are used in places where extra amount of light is necessary. This is cone-shaped and made of metal. 

Reflector trims are used typically for commercial applications. Being essential in the premises with high ceilings, like warehouses or workshops, hotels and offices, they might be installed in various utility areas of your house, such as bathroom or kitchen.

If you install them in a small living room, you might feel uncomfortable.

Open Trim:

Open trim looks very similar to baffle trim. The main difference is that it doesn’t have a ribbed interior.

The lack of ridges means that open trim doesn’t prevent glare like baffle trim. The benefit to this type of trim is brighter lighting. Open trim tends to provide much brighter lighting, to a much larger area, than other types of trim.

Select a light color open trim (such as white) to further enhance the brightness.

Open trim lights are ideal for illuminating larger areas. 

Eyeball Trim

Eyeball trim utilizes the same exterior trim as baffle trim and open trim, but pairs it with an adjustable interior light fixture. Sometimes referred to as adjustable trim, eyeball trim allows you to adjust the interior light fixture to customize lighting in your living spaces.

By simply rotating the fixture, you can aim the light exactly where you want it to illuminate. Their range of motion is typically 30° tilt and 359° rotation.

This type of trim is perfect for accent lighting.

Wall Wash Trim

Wall wash trim is a combination of baffle trims and eyeball styles. Though it doesn’t utilize interior ridges, it does have the same exterior trim design as a baffle and open trim. Inside is an adjustable light fixture that’s similar to eyeball trim.

There is also a half shield that partially conceals the opening of the light. This shield helps to evenly focus the beam of light on particular features in your living spaces.

The shield appears like a “scoop” to direct the light to a specific spot. These types of trims are ideal for accent lighting and spotlighting artwork, architectural features, or pieces of furniture.

For example, wall wash trim is perfect when you want accent lighting to highlight a painting.

Gimbal Trim

Gimbal trim functions almost exactly the same as the eyeball trim type. However, the major difference between the two is that the gimbal trim remains mostly flush with the ceiling. As a result, when the fixture is pivoted, the housing will get in the way of some of the light.

They are designed to be pivoted to provide directional light. More specifically, gimbal trim recessed lights direct downlight exactly where it’s needed. This type of trim is ideal for sloped ceilings and for highlighting accent walls in a home.

Shower Trim

This type of trim utilizes a tempered glass fixture cover. Not only does the cover keep the light fixture safe, but it also keeps moisture out. Shower trim recessed lighting is ideal for either wet or damp conditions.

Shower trims are best for bathrooms or any other areas that experience levels of high humidity. 

Material :

You also have two main materials to choose from, each of which helps give a certain design aesthetic and comes with certain benefits.

Plastic: Plastic, usually of polycarbonate, is a very common lighting fixture material. A basic plastic can work well in casual spaces. However, there are ornamented plastic styles for more regal or upper-class looks. Dark-colored plastics give a modern and sleek look. Plastic is also a good way to keep the cost lower.

Metal: Metals can give an austere look that is great in modern or industrial spaces. Steel is a very common material to find for its durability, as is aluminum because of how lightweight it is.

Trim Colors

A trim’s color can have a big impact on its output of the light. Dark colored trims absorb light and can result in as much as a 44% loss in light output.

The term Photometric Efficiency is used to describe the loss/efficiency of a trim.