From The Editor | January 3, 2024

Optical Filter's Role In Identifying Distracted Drivers

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By John Oncea, Editor


From fluorescence microscopy to Raman spectroscopy to medical imaging, optical filters are used in a wide variety of applications. Let’s take a look at these devices and how they can help target distracted drivers.

Optical filters are devices used to selectively transmit, absorb, or reflect light based on its specific wavelength or range of wavelengths. These filters manipulate light by exploiting the interactions between electromagnetic waves and specific materials or structures and are critical for some of the most demanding applications in automation, energy, medical imaging, security, and multi-element optical systems.

Edmund Optics summarizes 10 of the most popular types of optical filters that are available today, starting with bandpass filters. These filters have an extremely narrow band (<2nm to 10nm) or broadband (50nm and 80nm) transmittance across the substrate. They are crucial in applications like signal isolation in telecommunications or selecting certain spectral bands in imaging. Other filters Edmund Optics touches on include:

  • Longpass and Shortpass Filters: Longpass filters transmit light with wavelengths longer than a specific cutoff wavelength, while shortpass filters transmit wavelengths shorter than a cutoff. Longpass filters include cold mirrors, colored glass filters, and Thermoset ADC (optical cast plastic) filters and shortpass filters include IR cutoff filters, hot mirrors, and heat-absorbing glass.
  • Notch Filters: They are designed to block a specific narrow band of wavelengths while allowing the rest to pass through. They're useful in eliminating specific interference or unwanted wavelengths.
  • Interference Filters: Constructed using multiple layers of thin films to create interference effects, these filters can have very sharp transitions between transmission and blocking regions. They are used for high-precision applications like spectrophotometry.
  • Absorptive Filters: These filters absorb specific wavelengths, thereby preventing them from passing through. They are commonly used in laser systems and optical attenuators.
  • Polarizing Filters: They allow the light of a particular polarization orientation to pass while blocking others. They're used in applications where controlling polarization is critical, such as in photography or LCD screens.

The choice of filter depends on the application’s requirements, including the desired spectral range, transmission characteristics, and environmental conditions. Advances in nanotechnology and materials science continue to drive the development of new filter technologies with improved performance, compact sizes, and wider operational ranges.

Identifying Distracted Drivers Down Under And Across The Pond

Queensland, the second-largest state in Australia by area and the third-largest by population, is the sun-loving, beach-going traveler’s paradise. It enjoys more winter sunshine and warmth than just about anywhere else in the country and is known for its beaches, rainforests, open plains, and highlands.

Queensland also has installed mobile phone and seatbelt cameras throughout the state, located in areas where the use of a mobile phone or not wearing a seatbelt were contributing factors to crashes, according to the Queensland government.

The cameras – either fixed cameras fitted to existing infrastructure and operating 24 hours, 7 days a week or portable cameras used at random locations for shorter periods – take multiple images of every vehicle passing the camera. This includes capturing the registration number plate as well as images of the front seats of the vehicle.

“The cameras use artificial intelligence (AI) software to filter images and detect possible mobile phone use by the driver, or failure to wear a seatbelt by the driver and front seat passenger,” the Queensland government writes. “If no offense is detected, AI automatically excludes the images from any further analysis and the images are deleted. If AI suspects an offense, the image is passed on to the Queensland Revenue Office. An authorized officer will review the image to determine if an offense has been committed.”

These cameras are also being trialed in Victoria, the Australian Capital Territory, and South Australia and are in use in New South Wales (NSW) thanks to Acusensus, a provider of enforcement technology, which delivers 40% of NSW mobile speed enforcement camera services, including the provision of 55 mobile speed camera vehicles.

Acusensus technology is omnipresent in Australia. The company deployed the world’s first seat-belt non-compliance and illegal phone use enforcement camera program in Queensland, as well as introduced a multi-functional enforcement tool to simultaneously enforce illegal mobile phone use, speeding, and unregistered vehicles in Tasmania and Western Australia.

Acusensus solutions aren’t only used in Australia. In the U.K., the Humberside region (covering Hull, the East Riding, North Lincolnshire, and North East Lincolnshire) and Devon & Cornwall have installed Acusensus’ Heads Up system to simultaneously capture prosecutable evidence of illegal mobile phone use, seatbelt non-compliance, and speeding.

In a five-day operation in March 2023 in Humberside, Heads Up captured 54 drivers using a mobile phone and 225 not wearing their seatbelt. A six-week operation in Devvon & Cornwall in the summer of 2023 detected 1,045 drivers using a mobile phone and 1,329 not wearing a seatbelt.

Adrian Leisk, head of road safety for Devon and Cornwall Police, said, “When we trialed this technology last year, we were disappointed by the number of drivers detected not wearing seatbelts,” according to Fleet News. “The early results from our latest deployment show that there is also a problem with mobile phone use behind the wheel, which is both dangerous and illegal. We are employing this new technology to send a clear message to anyone who continues to use their phone behind the wheel – you will get caught.”

What About The Reflectivity Of Windshields?

Previous attempts to detect mobile device usage by drivers have been hindered by the high reflectivity of windshields during daylight hours. This issue is further compounded when reflections from large clouds obscure the view inside the vehicle. In such cases, using infrared light sources is not a practical solution, as the amount of IR illumination required to penetrate natural daylight would be resource intensive.

The solution, according to Unite.AI, “is the very oldest trick in the book – a cheap, physical polarizing filter that could be attached to roadside surveillance cameras, calibrated one time, and thereafter enable a clear look into vehicle interiors.”

Citing research conducted by the School of Computing at Newcastle University, Unite.AI notes that these polarizing filters help to reduce glare and reflections from glass surfaces, making it easier to identify the emitted light from phone screens.

Some systems may utilize infrared filters to isolate and detect the specific wavelengths emitted by electronic screens, as phone screens emit infrared light when in use. Also, cameras equipped with specialized sensors sensitive to particular wavelengths emitted by phone screens can aid in detecting the presence of a phone in use.

The combination of these filters and sensors allows these roadside cameras to spot specific light emissions associated with active phone usage while filtering out unrelated ambient light sources. Advanced image processing techniques then analyze captured images or video footage to detect and identify instances of distracted driving due to phone use.