LED Optics Explained
May 22 2019
When we think of an LED optic, we tend to think of a clear plastic lens that is placed on top of the LED itself to focus or spread the light. If this is your thought process, you’ve gone too far. Lets take a step back and look at the LED itself. See that small protective dome over the diode? That is actually called the primary optic which serves to protect and shape the output of the small diode. 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 (lenses, reflectors, TIR optics, etc.) to collect all that light and magnify its intensity towards the
Creating lenses and reflectors for leds (solid state lighting) is very different from just scaling untitled banners (1) they come down from other light sources. This seems like a reasonable way to create them, since leds have much smaller shape factors than other light sources, but they also differ in how they shine. As you can see from incandescent bulbs, they illuminate at 360 degrees, but leds are directional and only illuminate 180 degrees. This is due to the design of the LED, shown on the left, which consists of one or more chips mounted on a heat-conducting material and surrounded by the main optical element. Therefore, when the substrate is located on the back of the core, the maximum Angle LED can emit 180 degrees. LED failure
The main optical
The typical spatial distribution is what manufacturers use to describe the light coming from the main LED optical device. This basically means the shape or diffusion of light from the center of the diode. As we talked about earlier, the LED faces in one direction, so imagine a straight line going down from the center. The spatial distribution is measured in degrees of this central point.
Let's take the Cree xp-g2, which has a rating of 115 degrees, meaning the beam will extend 57.5 degrees on either side. Just because it is rated does not mean that you can get the entire lumen output of the LED across the entire spectrum. Like other light points, the light gets stronger as it gets closer to the center. Take a look at the "typical spatial distribution" chart of the xp-g2. Such a chart will appear on the emitter data table and can be found on all LED product pages on the website. Spatial distribution Cree xp-g2 LED
Along the central axis, the LED emits 100 percent relative luminous intensity, and the further away you are from the center, the less intense it will be. Assuming we are running 350mA Cool White Cree xp-g2, we know from the data sheet that under this drive current, the LED will emit 139 lumens at the central axis, namely the rated output. At 30 degrees from the center, the LED output drops to 125 lumens. Along the 40-degree distribution curve, the output is only 111 lumens. This continues to drop until 57.5 degrees and you only get about half the lumen output 70. Obviously, when you lose that much light output on the spectrum, you need an auxiliary lens or optical device to enhance the light and use LED brightness and efficiency to reach maximum capacity.
LED needs to be focused
High-power LED has been continuously improved and become an intelligent choice for various applications. As mentioned above, for many of these applications, such as interior point/bottom lighting, street lighting, building lighting and spotlight lighting, the transmitter and the main optical devices themselves do not provide sufficient strength to the target surface. We sneak into the transmitter output above, but another way to describe it is the distribution of the lambert light emitted by the transmitter. This basically means that the brightness of the observer is the same regardless of the position of the observer. If you've ever seen a naked emitter light up, you can see it immediately. Even if you are far away, you can still see the light source is very bright, it may even disturb your eyes.
Secondary optical devices are used to collimate the light into a controlled beam, bringing the full intensity to the area you need. Collimating rays travel in parallel, but due to diffraction and the limited physical size of the bare emitter, it is not possible to make the light completely parallel. It is important to note that the smaller the light source (emitter), the more efficient the process.
When describing how a second-order optical element or lens collimates a beam of light, we usually look at the viewing Angle or half-height full width (FWHM). FWHM is the angular width of the beam when the intensity at the edge is half that at the center of the beam. This is a useful way to classify optics, but it does not take into account the differences between certain optical platforms (diodes of different sizes). It's nice to know that optical devices with the same viewing Angle can vary greatly in beam strength and quality, depending on the optical design of the transmitter. On the optics page of our website, we tried to list all the different angles and FWHM of each LED we carried.
Secondary optical devices are not only used for collimating light, sometimes they are used to improve color uniformity and light distribution in the target region. Choosing the right optical element or lens depends on the application. Reflectors and TIR optical devices are used in many different applications and both have advantages and disadvantages.
Reflectors are easier to implement and cheaper to manufacture than TIR optics. The extent to which they collect and collimate light depends on their shape. Sometimes they also use different finishes to add texture or scatter light. In general, the physical size of the light source limits the optical selection. For on-board chip (COB) arrays or transmitters that emit such large areas, the only real solution is to surround them with reflectors.
Reflectors are used in most incandescent lamps, but there is a key drawback to using leds: most of the light from the center of the emitter comes out of the system without touching the reflector. This means that even with a narrow reflection system, a large proportion of the light will miss its target. This can result in loss of lumen output or unnecessary glare. Reflector light distribution
This is why it has become common, especially with improvements to high-lumen-density transmitters, which are encapsulated in TIR lenses to direct almost all the light towards the target.
A total internal reflection (TIR) optical device or lens is usually molded from a polymer and USES a refracting lens within the reflector. They are usually tapered and can be very efficient in reflecting and controlling LED light propagation. They usually work by allowing the lens to direct light from the center of how the TIR LED optical system works to the reflector, which then fires out in a collimated and controlled beam, narrow or wide, whatever you choose.
There is also an extra surface on the component that provides more opportunities to modify the lighting. These surface treatments (corrugation, sanding, polishing, etc.) diffuse light, widen the beam, or shape the distribution.
As a result, the optical -CARCLO- 10003-15_tvtir optical system is very suitable for LED in taking advantage of emitter characteristics. Other forms of light radiate heat outward, and leds emit heat from their bases, allowing these TIR optical devices to merge and completely enclose the top of the dome. This allows for more control as they are irradiated and controlled directly from the light source.
TIR optics is often used in outdoor lighting and has been greatly improved in indoor applications. They are ideal for narrow beam control, but are less effective in emphasizing diffuse and low glare.
The ratio of LED size to optical element size determines the beam Angle. If you want a narrow beam from your LED than this requires a smaller transmitter or larger optical device. Smaller emitters will limit output, while larger optics will really push the limits of injection molding. It is important to really understand what you are looking for (lightest, even expanded, etc.) and combine LED and optical components to meet your application requirements.
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Installing optical devices onto leds is actually quite simple, especially if you're familiar with LED power supplies. We provide a variety of TIR optical components from Carclo to work with our Cree and Luxeon LED products. In our optics section, simply select the LED you want to use and a list of optical components and optical element holders compatible with the product you want to use will appear.
The triple optical system works well with our LED stars because their legs fit directly into our star plate. Using a one-way TIR optical element, you will need a lens holder, which is a very important place for you to go to the optical page and see which stands are suitable for which LED. Untitled banner (2)
If you want to build your own lights, it's best to test a few different options to see which one provides the light you need. Stay tuned for our next area of LED optics, where we will test leds and optical devices together to understand the light they emit at different distances.
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