Introduction
In the world of optical product development, precision and innovation are key. Whether you’re designing automotive headlights, displays or any other optical system, understanding how the human eye perceives light and its dynamic nature is paramount. That’s where Ocean™ and its Human Vision module come in. In this blog post we will explore how this cutting-edge ray tracing software can revolutionise your R&D projects by simulating human vision in all its complexity.
General principles
Human vision is a remarkable sensory system. However, various factors can influence our perception of the world:
Figure 1 – Difference of color perception depending on photopic or scotopic vision.
Figure 2 – Contrast senstivity decrease with age, based on Owlsley,C.J., Sekuler,R. & Siemensne,D. Contrast sensitivity through adulthood. Vision Research 689-699 (1983)
Figure 3 – Depth of field vs pupil size
Figure 4: Night scene (mesopic) without glare (left) effect and with glare effect (right)
Figure 5 – Dark adaptation curve. Pirenne M. H., Dark Adaptation and Night Vision. Chapter 5. In: Davson, H. (ed), The Eye, vol 2. London, Academic Press, 1962
It is also important to remember that displays have a limited dynamic range, as the human eye has a wide dynamic range. This difference means that what we see on a screen may be slightly different from what we would see in real life scenarios.
To bridge this gap between simulation and reality, OceanTM introduces the Human Vision module. This module allows you to introduce several important aspects of human vision into your optical system simulations, providing insights that can greatly influence product development. Some of the elements listed above have already been covered in more detail in this blog post: Ocean™ Module : Human Vision.
Sensitivity Functions in Ocean
Vision sensitivity is the foundation of how we perceive the world, and understanding it is vital to the development of advanced optical products. In this section, we explore the nuances of vision sensitivity, specifically photopic, scotopic and mesopic vision, as well as the effects of age on visual perception. We’ll then show how OceanTM replicates these sensitivity functions to enhance optical simulations.
Photopic Vision – Day Vision
During the day, our vision is primarily based on the responses of the cones. There are three types of cones: S (short wavelength), M (medium wavelength) and L (long wavelength). This gives rise to colour vision, which is linked to colour spaces, in particular the CIE 1931 XYZ colour space.
Figure 6 - Photoreceptor cells of the human eye and retina.
Figure 7 - CIE 1931 Standard Colorimetric Observer functions used to map blackbody spectra to XYZ coordinates
Figure 8 - Eye sensibility depending on wavelength
In OceanTM, the simulation process involves translating spectral data into CIE XYZ values, which can then be mapped to RGB colours for visualisation. However, a gain factor is used to ensure accurate translation. This gain factor is calibrated to match the maximum response of a standard middle-aged observer, set at 683 lumens per watt.
Scotopic Vision – Night Vision
In low light conditions, our vision shifts to rely solely on rod cells. Unlike photopic vision, scotopic vision lacks colour perception. There is no equivalent to the CIE colour spaces for scotopic vision, and simulation involves integrating the received light over the scotopic luminosity function.
Within OceanTM, simulations involve the translation of spectral data into black and white images using the scotopic luminance function. As with photopic vision, a gain factor calibrated to the maximum response of a standard middle-aged observer is applied and set at 1700 lumens per watt.
These two images show the same scene in a photopic and scotopic environment:
Mesopic Vision – Twilight Vision
Mesopic vision occurs in the transition zone between day and night vision. It combines the responses of both cones and rods, resulting in a more muted form of colour vision. Mesopic vision does not have a standardised CIE colour space, as it depends on the global luminance of the scene, and there are no standardised human tests for mesopic vision.
Figure 9 - Dynamic range of the human visual system
OceanTM uses a method based on the paper : Color Appearance Model Applicable in Mesopic Vision – Satoshi Shioiri – Optical Review to simulate mesopic vision, taking into account a mixture of scotopic and mesopic values.
Figure 10 - Ocean's methods to to simulate mesopic vision
The three images below show the same scene in a photopic, mesopic and scotopic environment:
Day (light off)
Mesopic E = 10 lw (light on)
Night - Scotopic (light on)
The two images below show the same scene at night with mesopic and photopic vision:
Vision with Age:
In order to design products that appeal to a wide audience, it is important to understand how vision changes with age. Research based on this paper: Scotopic sensitivity during adulthood – Gregory R. Jackson, Cynthia Owsley (2000), has shown that sensitivity decreases with age, particularly in scotopic and photopic vision. To accommodate these age-related changes, OceanTM adjusts the gain factors used in simulations. This means that for older individuals, the simulation will take into account their reduced sensitivity.
Figure 11 - Scotopic and photopic sensitivity as a function of age.
The images below show how the perception of the same scene varies with age (Photopic vision):
The images below show how the perception of the same scene varies with age (Scotopic vision):
Vision with Time Adaptation
The human eye requires time to adapt to rapid changes in luminosity. There are two types of adaptation:
Light Adaptation: This occurs when transitioning from dark to light environments and involves a rapid adjustment of the eye’s detection threshold.
Dark Adaptation: Dark adaptation takes place when moving from bright to dark environments and is a much slower process.
Within the OceanTM simulation framework, these adaptations are simulated by modifying the gain factors in the luminosity functions (Photopic luminosity function for light adaptation, Scotopic luminosity function for dark adaptation). This ensures that your optical designs take into account the dynamic nature of human vision.
Figure 12 - Light adaptation. For a mid-age observer (20 yo), at a given time T, light and dark adaptation are simulated by reducing the gain factor of luminosity functions.
Figure 13 - Dark adaptation. For a mid-age observer (20 yo), at a given time T, light and dark adaptation are simulated by reducing the gain factor of luminosity functions.
Example of light adaptation for a 20-year-old individual:
After 1 second
After 1 minute
After 20 minutes
Example of dark adaptation for a 20-year-old individual (Mesopic):
After 1 second
After 1 minute
After 20 minutes
Example of dark adaptation for a 20 year old individual (Scotopic):
After 1 second
After 1 minute
After 20 minutes
Time Adaptation with Age
Age also influences the speed of light and dark adaptation. Research of G R Jackson 1 , C Owsley, G McGwin Jr., Aging and dark adaptation, suggests that older individuals require more time to return to their baseline sensitivity levels. OceanTM incorporates this data, adjusting the gain factor based on age and time to provide a more accurate representation of real-world visual experiences.
Light adaptation is also prolonged for older eyes, taking approximately three times longer than dark adaptation. To accommodate this, the gain factor of luminosity functions is adjusted by taking into account the increase in time due to aging.
Additionally, older individuals are more susceptible to glare when transitioning from dark to light conditions, a critical factor to consider in many product design scenarios.
Example of dark adaptation depending on age (Mesopic):
20 yers old - After 1 second
20 yers old - After 1 minute
20 yers old - After 20 minutes
50 yers old - After 1 second
50 yers old - After 1 minute
50 yers old - After 20 minutes
90 yers old -After 1 second
90 yers old - After 1 minute
90 yers old - After 20 minutes
Example of light adaptation depending on age (Photopic):
20 yers old -After 1 second
20 yers old - After 1 minute
20 yers old - After 20 minutes
50 yers old -After 1 second
50 yers old - After 1 minute
50 yers old - After 20 minutes
90 yers old -After 1 second
90 yers old - After 1 minute
90 yers old - After 20 minutes
Practicle applications for product design
Now, let’s explore how OceanTM, along with its Human Vision module, can revolutionize the way you approach optical product development:
Realistic Simulations: OceanTM empowers users to simulate optical systems by accounting for variations in human vision. By incorporating photopic, scotopic, and mesopic vision, you can ensure your products perform well in diverse lighting conditions. This means you can design products that work effectively in both bright daylight and low-light conditions, making them more versatile and user-friendly.
Age-Responsive Designs: With the ability to model age-related changes in vision, you can tailor your designs to suit a broader range of users. This can lead to more inclusive and user-friendly products that cater to individuals of all age groups.
Photopic expected result
Reality for a 20 year old individual
Reality for a 90 year old individual
Accurate Glare Analysis: OceanTM‘s Human Vision module allows you to analyze and mitigate glare effects caused by the cornea and pupil. This is crucial for designing automotive headlights, display screens, and other products where glare can be a concern. By reducing glare, you improve both the safety and user experience of your products.
Time-Adaptive Solutions: Simulating light and dark adaptation enables you to design products that are not only visually comfortable but also safe. This is particularly important for applications where rapid changes in lighting conditions occur, such as in automotive lighting systems.
Research and Development Efficiency: The ability to conduct these simulations within OceanTM can streamline your R&D processes. It allows you to test and optimize your optical designs in a virtual environment before physical prototypes are built. This not only saves time but also resources and reduces the likelihood of costly design errors.
User-Centric Design: OceanTM‘s Human Vision module provides invaluable insights into how your products will be perceived by different age groups. By considering the varying sensitivity and adaptation characteristics of different age groups, you can create designs that prioritize the end-user’s visual experience. This user-centric approach can set your products apart in a competitive market.
Conclusion
When it comes to optical product development, precision is non-negotiable. OceanTM, with its Human Vision module, allows R&D engineers to create optical systems that accurately replicate the complexities of human vision. By accounting for photopic, scotopic, and mesopic vision, age-related changes, and time adaptation, you can develop products that are not just innovative but also user-friendly, safe, and versatile. This technology not only streamlines your research and development process but also ensures that your products cater to a wide range of users. In a world where user experience and safety are paramount, OceanTM‘s Human Vision module is a game-changer for optical product development.
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