Photometric

Anyone who has been out at night in open country knows what dark really means. Stepping outside on a moonless night can be a jarring experience. Most of us have lived our lives bathed in outdoor light, whether from streetlights, vehicle headlights, flashlights, or even candles. Given enough time in the darkness, eyes adjust enough to make out forms, but not enough to see trip hazards or colors.

That’s an inconvenience for most. But for military members or first responders, the inability to see in the dark with better resolution can make the difference in a survival or rescue situation. The central components of a night vision imaging system (NVIS) are the night vision goggles (NVG) worn by operators in those conditions. NVGs electronically amplify the available visible and infrared light for the operator, allowing finer detail to be seen.

Night vision imaging system in the cockpit

For NVIS to be useful, the ambient light from instruments and other sources must not compete with the enhanced view seen by the operator. This is especially true for NVG-equipped aircraft pilots and vehicle drivers carrying out covert missions in total darkness. The environment of instrument displays and indicators need to be visible to dark-adjusted eyes without interfering with the NVG’s ability to amplify the outside environment.

Lighting Equipment Categories and Requirements

Several categories of lighting and marking equipment are listed in MIL-STD-3009, including backlit displays, instrument panels, buttons, switches, indicators, and area illumination. The basic requirement for NVIS Compatible lighting equipment is that it can be viewed comfortably by the naked eye and that it not interfere with the NVIS. NVGs are typically used to view the surrounding environment while operators look under NVG to view close-up instruments with dark-adjusted vision. However, exterior lighting used to mark aircraft, vehicles, roads, and runways can be designed using infrared sources to be invisible to the naked eye while appearing through NVGs. Depending on the application, lighting equipment falls into three main categories:

• “NVIS Compatible” lighting in an instrument panel, backlit display, or interior lighting needs to be visible by the naked eye while not being at a level or color that would interfere with the operation of the NVG.
• “NVIS Friendly” lighting can be viewed through the NVG without saturating the view or have blooming effects. This could apply to interior or exterior lighting systems.
• “Dual Mode” lighting can be selected to be visible to the naked eye or through NVGs only. This typically applies to exterior lighting equipment used to mark vehicles or locations, such as wingtip lights and runway edge lighting, so they can operate in total darkness without being detected.

NVIS Friendly or Dual Mode lighting viewed through NVIS

Colors

Colors of illuminated symbols and numbers displayed on instruments need to meet requirements for chromaticity, which is the quality of color. Four colors are defined and given specific chromaticity values in MIL-STD-3009 – NVIS Green A and B, NVIS Yellow, NVIS Red, and NVIS White. The reference points from the CIE 1976 color space reference standard are shown in the figure below.

NVIS lighting chromaticity limits from MIL-STD-3009

NVIS-compatible spectral response from MIL-STD-3009

Standardizing a set of compatible colors assures that light sources will be consistent and compatible with night-vision equipment in all applications. MIL-STD-3009 defines three classes of NVIS filters based on wavelength. The filter relative responses are shown as A, B, and C in the response curves in the figure above.

Spectral Radiance and NVIS Radiance

Spectral Radiance (mW/cm2) is the primary measurement used to determine NVIS compatibility. Because of the extremely low visible light and infrared limits, Elite’s Photometric Testing lab is equipped with a high precision spectroradiometer and dark room to ensure, repeatable accurate measurements. The raw spectral radiance values are then weighted and scaled based on the NVG filter response to calculate NVIS Radiance (NRa and NRb). The specifics for those limits and the measurement techniques are contained in MIL-STD-3009, MIL-L-85762A, and SAE ARP5825A.

Spectral radiance test setup, showing positions for reflected radiant intensity and direct radiance

Spectral radiance test setup in Elite’s photometry lab

Radiant Intensity (mW/sr) is spectral radiance measured from a Lambertian reflectance plaque, which provides a standard reference for determining the beam pattern of the light source. A goniometer (positioner) is used to rotate the light source to point varying angles at the reflectance plaque. The same weighting and scaling are applied to calculate NVIS Radiant Intensity (NRIa and NRIb) typically required for exterior, marking, and signal lighting equipment.

Tests are typically done with multiple samples measured at different levels and angles. Extremely low light sources take more time to measure and add to the overall time required for the test project.

NVIS Compatibility Testing at Elite

Elite is equipped to perform the full range of NVIS compatibility tests assuring compliance with MIL-STD-3009, MIL-L-85762A, and SAE ARP5825A. Contact the experts at Elite for information on NVIS requirements and how they apply to your product. Put Elite’s industry-recognized expertise to work for you.

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Elite is proud to announce that it has received ISO 17025 accreditation for Photometric Testing from the American Association for Laboratory Accreditation (A2LA, Certificate 1786.02). This is a major milestone for our photometric testing team since launching this new service in 2017. Combined with our existing scopes of accreditation for EMC/EMI Testing, Environmental Stress Testing, and Product Certification, this achievement demonstrates our commitment to delivering high-quality testing services for the lighting industry in one location. And our customers can be confident that our test results will be accepted around the world. Elite is also an approved laboratory for the DesignLights Consortium (DLC) qualification program, including IES LM-79 luminous flux and color measurements.

Our scope covers a wide range of test methods for automotive exterior, aerospace, and general lighting products – including FMVSS 108, SAE, FAA, ICAO, and IES specifications. Our laboratory is equipped with a 2-meter integrating sphere system and Type A goniophotometer for accurate measurements of luminous flux (lumens), luminous intensity (candela), flash energy, optical power, and color for lamps and luminaires up to 48” wide. Please visit our Quality Assurance page to download our full scope of accreditation.

In July 2018, we hosted our second Photometry Workshop covering test preparation for steady and flashing lights. It was a great opportunity to learn from our photometric test team and Bob Czajkowski, a lighting industry expert from Federal Signal and SAE Standards Committee chair, as well as gain hands-on experience in our photometry lab. We’re looking forward to planning our next workshop for 2019.

Contact us today to discuss the testing requirements for your lighting product and how we can help you succeed with accredited test results.

Third-party ISO 17025 accreditation with A2LA is an internationally-recognized quality assurance process that verifies the technical competence, facilities, management systems, and personnel qualifications of a testing laboratory. Since 1986, Elite has been continuously accredited and our scope has steadily expanded along with our facilities and testing services.

Labels:

• Elite Experts
• Quality Assurance
• Photometric Testing
• Lighting Industry
• Automotive Industry
• Aerospace Industry

In an effort to provide lighting manufacturers with a way to validate every aspect of their product in one location, we’re excited to announce the opening of our new photometric testing lab—a state-of-the-art addition that now complements our EMC and environmental testing services.

Since everyone loves a good time-lapse video, here’s one showcasing the construction of the new addition.

More Complex Lighting Systems Call for More Complex Testing
Due to the growing complexity of today’s lighting systems, producing accurate test results has become equally as complex. Lighting innovations have extended product life, reduced energy consumption, and enhanced illumination, an in turn has increased the scope of compliance testing that’s needed. For example, compliance with FCC emission limits, CE Mark Directives, and water/dust Ingress Production (IP) may all be necessary for lighting products produced today.

State-of-the-Art Photometric Testing Equipment
Our new photometry lab is equipped with state-of-the-art measurement equipment (more on that below) to help achieve compliance with these directives by ensuring precise, repeatable results for practically any application, including the automotive and aerospace industries.

This advanced equipment includes a Type A goniophotometer for automotive exterior lighting and other forms of directed light sources. The goniophotometer also simulates Type C for accurate LM-79 measurements. We’ve also equipped the lab with high-precision spectrometers with NIST-traceable calibration sources, as well as an integrated power supply and analyzer with software control. Every application is provided with custom mounting fixtures for those difficult-to-fasten products.

If you are in need of testing for your automotive, aerospace, airport, or even general lighting products, please contact us today.

Labels: Photometric Testing

One of the most exciting additions at Elite’s new North Annex is a completely new service – Photometric Testing. It is the perfect complement to our proven EMC and Environmental testing services that we currently perform on lighting products and we are committed to delivering it with the same scheduling flexibility and customer service that you expect from Elite.

Recent innovations such as LEDs and wireless connectivity for IoT (Internet of Things) applications have increased the electrical complexity of lighting products with digital controls, power electronics, and transmitters. While those innovations dramatically reduce energy consumption, extend product life, and enhance illumination, they also increase the scope of compliance testing beyond the photometric performance of the luminaire. Today’s lighting products may require compliance with FCC emission limits, various CE Mark Directives, and water/dust Ingress Protection (IP). Elite can help you navigate the maze of compliance requirements to qualify your products and get them to market faster.

Starting in June, Elite will serve the complete compliance testing needs of lighting product manufacturers – covering EMC/EMI, electrical, environmental, and photometric requirements – in one location. Our new Photometry Lab is designed for automotive and aerospace lighting applications with the flexibility to accommodate most types of consumer and industrial applications as well. It is equipped with a state-of-the-art Type A goniophotometer and a 2-meter integrating sphere with enough room for even the largest luminaires. For LED testing per IES LM-79, our Type A goniophotometer can accurately simulate Type C geometry.

Elite’s Photometry Lab will be open in June, so contact us today to find out how we can complete all of your lighting product compliance testings in one location. Stay tuned next month for more on the final preparations of our new North Annex and how it will improve our ability to serve our customers’ needs with more testing capabilities, greater capacity, and shorter lead times.

Labels:

• Elite Expands capabilities
• New Services
• Photometric Testing
• Lighting Industry