Optical Design & Engineering
Background: There are many different kinds of light sources that produce differing amounts and different colors of light. Originally, light at night was created with flame. When bulbs were invented by Edison, light came from a glowing filament, as is seen with the common incandescent bulb. Later on, other lights came to be powered by a glowing gas, as in a common fluorescent bulb. And the newest light sources like LEDs use electronics, rather than heat, to create light. But regardless of the type, all of these devices produce light. And the technology that bends, aims or spreads light is referred to as Optical Design and Engineering.
Continental’s Optical Engineers utilize an Optical Software program which first designs lens and reflector devices that collect the light rays emanating in several directions from an LED. The engineer further refines the lenses or reflectors to focus, concentrate or re-direct the rays. Optical Design permits the Engineer to determine where the light will go, and also where it will not go, keeping it from going in directions where it is not needed or wanted.
A good example taken from Continental’s 25 year Optical Design & Engineering Case Studies is a low beam headlight for an automobile, where light is needed on the driver’s side down on the road, so that he can see the road at night, but out of the eyes of the on-coming driver.
As mentioned above, the Continental Optical Design Engineer harnesses the light rays from an LED, and uses lenses or reflectors to change the path of the light in different ways, depending on the need or the specific lighting product. The Continental Optical Design Engineer can use a lens to focus the light in one location, as one commonly sees with a magnifying lens. The Optical Design Engineer could also create a concentrated beam of parallel rays with either a lens or specially designed reflector, as seen with a spotlight. Lastly, the Engineer could use different lenses and reflectors to spread the rays of light out evenly on a surface, as one sees in a movie theater with the projector.
LED Lens Options
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With an LED there are many different styles of lenses used by the Continental Optical Design Engineer. There are lenses that fit directly on top of the LED chip, and other lenses that can clip-on an inch or so away from the LED, to change the path of the “rays.” One commonly sees these on the red LED Center High Mounted Stop Lights (CHMSLs) on the rear of every automobile. One often sees an outer lens that provides optical treatment and serves as a cover to protect the LEDs from water, dust or the environment. All of these lenses are commonly seen on LED and non-LED automobile headlamps.
Stages of Optical Design Engineering
The Continental Optical Design Engineer is skilled at reducing costs by maximizing the light output of the light source such as Light Emitting Diodes (LEDs), thus reducing the number of LED’s required in the fixture. This saves cost and energy.
To develop an optical pattern, the Continental Optical Design Engineer must determine the answers for the following four questions:
- How much light is needed?
- What color of light is needed, which includes the different colors of "white" light?
- Where is this light needed, and where is it not needed?
- What are the energy, packaging and environmental restraints of the fixture?
The Optical Design Engineer then selects the correct type and number of LEDs that will meet the lighting requirements in #1 and #2 above. Advanced Optical Design software is utilized to create a computer simulation of the rays of light from the LEDs, then modify the light with lenses, reflectors, or both, to meet the needs in #3 above. A good example of a Continental Optical Design Engineer’s work can be seen to the right with an actual ray tracing design.
The Optical Design Engineer can also use advanced Optical Design Software to simulate the actual illumination of a lighting component's target area to see what the rays actually look like after passing through the lenses and reflectors in the design. These rays are also called “beams,” and the collective pattern they create on a target area is referred to as the beam pattern.
Beam patterns actually include the measurement of how bright the light output is from all of the rays in the full beam pattern. When components are sold, the manufacturer is required to have a beam pattern in the product literature, referred to as a photometry report. Photometry is from the words photo or light, and -metry which means “to measure.” So, a photometry report is a measurement of the light coming from a lighting component, as it hits its target such as a wall or the ground, as with a street light. Continental has a test lab that can validate the simulated beam pattern from a lighting product, and measure the light at different test points.
Photo-realistic Light Simulation
Much as Steven Spielberg used advanced animation software to create dinosaurs in the movie Jurassic Park, the Optical Design Engineer utilizes different advanced Photo-realistic Simulation software to create what appears to be an actual picture or color photograph of a lens, reflector or an entire lighting component. These are created from actual Computer-Aided-Design (CAD) data so that the end user can actually see an accurate picture of the finished lighting product before it is made. This allows designs to be reviewed and changed early in the process before molds and parts are made.
Buyer Beware: LED Lighting
Light output is measured in lumens. Most people are familiar with the light output of a traditional incandescent 100 watt light bulb, which is usually about 1700 lumens. Newer Compact Fluorescents can give the same amount of light at lower wattage and are usually sold based upon how they compare to an incandescent bulb. Lighting specs from architects or engineers will indicate the amount of light required for the fixture in lumens and will often include the photometry required by the fixture; that is how much light must fall where in the beam pattern.
As the LED market has grown quickly, many claims have been made on the lumen output and photometry of LED fixtures. While there are many reputable companies that meet or exceed their spec sheets, enough fly-by-night firms have flooded the market with false claims that customers are wary of LED products. To standardize these measurements and enhance consumer confidence, a new test procedure has been developed.
A New Test Procedure: LM-79-08
The lighting industry looks to the Illuminating Engineering Society of North America (IES) for lighting measurement test procedures. These test procedures are designated "LM" for lighting measurement, followed by an ordinal number, and the year of adoption or revision. They are developed by the IES Testing Procedures Committee, whose members include representatives of industry, research institutions and testing laboratories. The LM – 79 test is a test performed by an independent, certified lab that measures LED light fixtures to ensure they meet the product specifications claimed by the manufacturer.
Sponsored by the Department of Energy and similar to a nutrition label, the Lighting Facts Label provides a quick summary of product performance data. Including this label on a product is voluntary at this time, but many major manufacturers have joined in on this program. Expect to see this label popping up on light sources and fixtures in the future.