How do optics work with LEDs? Many think it is simply the plastic lens on the top of the bulb covering the diodes that disperses the light. However when you dig deeper into the components, there is more to it.
In taking a closer look at the LED diodes themselves, they have an outer casing. This is one part a protective measure but these also act as the primary optic. Even still, this primary optic is not focused enough and lacks strength over a distance. This is where the lenses, reflectors, and so on come into play as they take all the light within a given bulb or fixture and magnify the intensity based on how the optics are designed.
As LEDs were born, lenses and reflectors had to be entirely re-designed. They could not be re-used from previous light sources as LEDs emit light in a different manner. Older bulbs like incandescents have a 360° spread. The directional nature of LED results 180° illumination and with the substrate underneath the diode, it cannot be any wider than that.
Manufacturers continue to find new ways to manipulate LED optics to become smarter to suit more applications. Reflectors and TIR optics have become two of the most common ways. In terms of cost and ease of creating, reflectors are hard to beat. They come in varying sizes and how they collect and disperse the light will depend on their shape. With chip-on board LEDs, the light area is so large that a reflector is the only effective option. The downside to reflectors? The vast majority of light rays coming from the center emitter pass through the LED light source without even hitting the reflector. This means a good portion of the light will stray wide off it’s intended target and/or will create glare.
This is where Total Internal Reflection (TIR) Optics come in. Particularly with high lumen-density light sources, enveloping them with a TIR lens will ensure more control of where the light will be emitting. TIR lenses are mostly injection molded from polymers and utilize a refractive lens inside a reflector. They are far more efficient in controlling LED light spread. The lens directs light from the center of the source to the reflector, which then sends out a controlled beam in whichever direction is specified. On top of this, additional surface treatments (frosted, rippled, etc) can be applied to shape the light distribution.
TIR optics work fantastically with LEDs as these optics fit perfectly surrounding the top of the LED. This allows for total control direct from the light source. TIR optics initially were used primarily with outdoor applications but have made progress with indoor lighting. They are still best used with tight, narrow beams and don’t work quite as well when the goal is wide, diffused light.
As with any decision when it comes to lighting, make sure you take into account what purpose the light fixture is supposed to provide and then choose the optics that best suits your need.