Entrusting laser risk management to PISÉO means choosing technical excellence, maximum safety for your products, and regulatory compliance.

Please do not hesitate to contact us with any questions you may have about the LASER safety of your devices.

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Use of materials in optical design

The optical design of high-performance systems requires perfect mastery of the optical properties of materials.
A large percentage of the engineering projects conducted by PISÉO involves optical design. Our experts design systems that meet our customers’ most demanding requirements, then model and evaluate their performance using optical simulation software that integrates the materials’ optical properties. The skills and resources they mobilize allow them to consider a variety of materials and quickly offer their clients appropriate choices for their optical systems.

For each project, we can offer you perfectly adapted materials for your optical systems, taking into account your technical needs, industrial constraints, and the regulatory requirements specific to your application.
Whether it is to develop precision optical systems, guarantee maximum luminous efficiency, or meet strict performance and safety standards, PISÉO is committed to providing you with tailor-made and optimal solutions.

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PISÉO stands out for its expertise in designing custom LED-based UV-C sources adapted to the specific needs of its customers in various application areas. This expertise has proven particularly valuable during the COVID-19 epidemic, which generated a significant increase in the need for disinfection solutions. At the same time, the performance of UV-C LEDs has improved considerably in recent years, as shown in our UVC LED report.

Mercury-based UV tubes, historically used for disinfection applications, will be gradually withdrawn from the market by 2027. This deadline encourages users to review their strategies and look for alternative solutions. LED-based UVC sources now offer a viable and more environmentally friendly alternative. However, in order to reap all the benefits, the transition to this new technology requires specific know-how, which PISÉO has developed over the years.

UVC LEDs

The design of an appropriate UVC LED source takes into account the optical, electrical, and dimensional characteristics of the components available on the market. As the COVID-19 epidemic has sparked a strong craze for disinfection devices, many manufacturers have developed a portfolio of more or less effective UVC LEDs. It is, therefore, essential to have a good knowledge of the broad range of these components in order to make informed choices. Performance tests in an optical laboratory, such as PISÉO’s, can be useful for discriminating between products and ensuring the correct characteristics.

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Design of UVC Sources

The specific application cases of UVC LED sources require a design approach that draws on a knowledge of physics, as well as biology and chemistry. For a disinfection source, for example, it is crucial to know the sensitivity of microorganisms to ultraviolet radiation in order to determine the dose and spectrum required to deactivate the DNA and RNA molecules of these microorganisms. This is the germicidal effect of the UVC source. Examples of doses for air disinfection are given in the International Commission on Illumination document CIE 155:2003.

Once the dose and spectrum have been determined, it is necessary to consider the environment in or on where the biological or chemical reaction will occur. Indeed, characteristics such as the geometry and materials of the exposed or fluidic surfaces must be considered during the design to guarantee the efficacy  and durability of the systems developed.

Finally, LED system design know-how is required to ensure product performance and reliability. Once the component has been chosen, the integration of UVC LEDs requires in-depth work to provide the right level of energy illumination and maintain it over time, thanks to a precise optical design, suitable electronics, and efficient thermal management. The latter aspect is particularly crucial given the heat dissipation requirements of UVC LED components.

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In conclusion, the transition to UV-C sources represents an opportunity to improve disinfection and environmental protection practices. Thanks to our expertise and commitment to innovation, PISÉO is positioned as a partner of choice for all companies wishing to adopt this cutting-edge technology. To learn more about our UVC source design services and discover how we can support you in your projects, do not hesitate to contact us.

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Thanks to the unique combination of its expertise and the resources of its testing laboratories, PISÉO has the capacity to carry out comparative studies of photonic products and components. These studies are carried out independently and impartially, based on accepted test protocols.

The benchmark analyses conducted by PISÉO apply to LED, LASER, photodiode, or imaging sensor components, as well as to all products that integrate them: lighting, cameras, screens, AR/VR headsets, and many others.

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What is Optical Engineering?

Optical engineering includes all stages of design, development, and industrialization of an optical function. It requires strong skills in optics, in-depth knowledge of photonic technologies (LED, LASER, imagers, detectors, materials, surface treatment), extensive industrial experience (manufacturing process, assembly), and cutting-edge design and optical characterization tools.

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What is stray light?

Stray light refers to unwanted and unintended light in an optical system.

These light rays are generally due to surface scattering of optical and mechanical components. Stray light can also come from internal reflection between components, unwanted surfaces, or surrounding light.

They can appear in different ways in an image:

• A veil (veiling glare) resulting from the diffusion of light on the edges of the lenses or their surface.

• A ghost image: a sharp image seen by the sensor due to internal reflection on the surface of the lenses.

• A halo (flare): a more diffuse image closer to the light source.

• A starburst effect: linked to the shape of the diaphragm of an imaging system that diffracts light. This can be desired in photography for an artistic effect.

How to reduce stray light?

To reduce stray light, it is essential to detect its presence and understand its causes.

Very often, the problem is first detected at the prototype stage and in tests carried out in the laboratory. 

Indeed, stray light phenomena are generally not considered when designing an optical imaging system by means of simulations  in sequential mode (using a Zemax, for example). Stray light issues require careful consideration of the energy aspect and non-sequential propagation. A tool like LightTools, mastered by PISÉO experts, is well suited for this.

To assess the risks of these phenomena during the design or in an existing system, we create complete models of the optical components and their environment (mechanical, light sources) in this tool, faithful to reality. These models also account for the optical properties of materials (refractive index of lenses) and surfaces (BSDF, surface deposits, roughness). We then use the model to perform simulations that highlight the effects of stray light and investigate their causes.

Once the causes are known, we can act on the system and propose improvements: geometry of optomechanical components, the addition of a baffle, anti-reflective coating, etc.

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Article written by Julie BONNETTO

Julie Bonnetto is a specialist in the design of industrial optical systems. She holds an Engineering degree in Optics, Photonics, and Industrial Vision, and a Research Master’s in photonic micro- and nano-structuring obtained at Telecom Saint-Etienne. Before joining PISÉO, she held engineering positions in the optical design and development of LED lighting systems at SIGNIFY (ex Philips Lighting), then LED indicators and lights operating in harsh environments at MAFELEC. His responsibilities within PISÉO include high-stakes optical design studies in fields as different as lighting, automotive, health, telecoms, luxury watchmaking, and biometrics.

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With their industrial experience, PISÉO’s experts accompany you throughout your projects, from idea to industrialization. Their services include optical engineering, design, characterization, system design, imaging analysis, optical calibration, and measurement, as well as prototype manufacturing and testing.

Thanks to their know-how, their technical means, and their industrial experience, PISÉO’s experts can meet the specific needs of each customer in terms of design and optical simulation.

What is optical design ?

Optical design is the process of designing and developing optical systems. In this process, an optical engineer considers many physical factors. These include spectral distribution of light, photometry, colorimetry, optical properties of materials, spectral response of illuminated bodies and geometry of components. An engineer also considers constraints and objectives related to the intended use.

Optical design is a multidisciplinary subject that requires a thorough knowledge of both mathematics and physics, as well as a great deal of experience. It also requires a good ability to understand the needs of the application for which the system is intended.

The design process begins with the determination of the optical performance to be achieved according to the intended use. These depend on the type of system considered and the applications, whether it is lighting, imaging, or display. Depending on the systems, we will therefore specify details including illumination, luminance, uniformity, contrast, color temperature, focal length, field of vision, spot dimension and spatial frequency.

Subsequently, the optical engineer will endeavor to imagine and evaluate optical systems to meet the objectives set. For this, they will perform sizing calculations, numerically model the solutions envisaged and simulate their performance using appropriate tools. This operation can be repeated as many times as necessary until they get an optical system capable of meeting the fixed performance requirements.

At the end of this work, they provide details of the various optical components created, integrating all the mechanical interfaces, taking into account the tolerances linked to manufacturing and assembly. Finally, the experts will prototype and test the system using appropriate optical measurement equipment.

Optical design comes into play in many industrial areas including lighting, automotive and transportation, defense, space, medical, manufacturing, photography, and more.

PISÉO’s definition of optical design

PISÉO understands optical design in a broad way. The optical system is considered as an assembly that integrates opto-mechanical and opto-electronic components, or even software. Indeed, only an overall system approach that considers all the parameters involved makes it possible to achieve an optimized design that will be able to meet the project objectives in all respects. In this way, our optical design work considers the application needs for ultraviolet (UV), visible (VIS) and infrared (IR) radiation. It considers the physical and economic characteristics of photonic components such as Light Emitting Diodes (LEDs), lasers, photodiodes, imaging sensors, materials for optics and surface treatments, as well as environmental and industrial constraints. In addition, we benefit from the close links with Yole Group analysts, who permanently watch photonic technologies, guaranteeing customers solutions at the cutting edge of progress.

Why entrust your optical design to PISÉO experts?

Coming from large groups and Small and Medium Enterprise (SME) leaders in their fields, PISÉO’s experts have extensive industrial experience in the design and manufacture of optical systems. With great rigor, they put their know-how at the service of our customers.

The numerous research and development projects carried out in all fields constantly develop our experts’ knowledge. They also rely on their cutting-edge technical resources including proprietary calculation and analysis tools, design, and simulation assistance software such as Zemax, LightTools and Rhino, and an accredited test laboratory. The latter allows them to precisely characterize the optical performance of the photonic components selected and of the systems designed by them from model to prototype to finished product.

PISÉO experts have a unique combination of know-how and technical means. They are thus able to support your company’s development by designing and industrializing, in a rapid and reliable manner, simple or complex optimized optical systems in response to all your needs.

After over 10 years in existence, PISÉO’s innovation platform has supported many customers globally in their industrial optical system projects. Examples include a high-power infrared illuminator for an industrial specialist in surveillance, endoscope imaging for a world leader in medical systems, redesign of a lens for a lighting SME and redesign of a light guide for an automotive player.

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Compliance with standards constitutes a solid basis for ensuring product compliance with the requirements of various international regulations and is an essential prerequisite for marketing products.

Designers, manufacturers, and marketers of products with high optical content can rely on PISÉO to guarantee the conformity of the devices they develop and market.

Like our many satisfied customers, you can trust the regulatory and normative analyses of PISÉO experts to ensure that your products comply with current international norms and standards.

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Their ability to emphasize lines and create signatures make them particularly attractive to designers and architects. Their low thickness and robustness allow them to be easily integrated into many systems.

In addition, their exceptional ability to guide light makes it possible to produce large luminous surfaces with excellent uniformity.

In these guides, LEDs are placed on the side and not under the surface to be illuminated. This arrangement makes it possible to reduce the number of LEDs while obtaining large, uniformly luminous surfaces in an extremely compact volume.

The reduction in the number of LEDs results in lower manufacturing costs for the manufacturer and a reduction in the system’s power consumption for the end customer. Indeed, to obtain a uniformity of 80% on the surface over such a small distance using LEDs placed under the surface, much more effort is needed than in the case of tangential lighting.

The low thickness of the guides (only a few millimeters) allows them to be easily integrated into many display and signage systems.

However, the design and production of light guides to achieve the desired luminance, uniformity, and illuminance require first-rate know-how and technical resources. Thanks to their vast industrial experience, their leading optical simulation tools, and their photometry laboratory, PISÉO experts can reliably and efficiently support you in developing all types of lighting systems based on light guides.

Luminance uniformity from the light guide

From a photometric point of view, these guides’ ability to conduct light makes it possible to obtain high luminances on large luminous surfaces. The luminance uniformity obtained is also excellent, with values above 80%.

However, the design of the optical systems is crucial and requires particular expertise to obtain such results at an acceptable cost.

Only a suitable combination of the correct LEDs, their operating points, materials, and surface treatments in a suitable architecture will make it possible to achieve the expected quality.

PISÉO has the skills and tools to reliably design, simulate, model, optimize, and characterize lighting systems using light guides, as well as any other system using photonic technologies.

For this, we rely on:

• the expertise of our engineers (Optics, Mechatronic Systems, Materials),

• our optical design and simulation tools, such as the ZEMAX Optic Studio and LightTools

• our proprietary algorithms

• our extensive materials database containing optical properties characterized in the laboratory

• our COFRAC-accredited characterization laboratory (scope available at www.cofrac.fr).

Our Westboro Photonics P1230U 12.3 MP video-luminancemetry  camera and its lenses allow us, for example, to carry out 2-dimensional luminance measurements quickly and precisely. The luminance level and uniformity of any luminous surface can be characterized.

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Light guide optical design and simulation

Light guides have several advantages: ease of integration, optimum performance with few LEDs leading to lower energy consumption than a multi-LED system, ease of production by machining or plastic injection, and aesthetic rendering, which are particularly appreciated by designers, manufacturers, and architects. However, a light guide obeys optical physical laws that must be respected to obtain all the advantages stated above.

The first step – coupling the source with the guide – is crucial to avoid losses between the LED and the first input face. The characteristics of the LED and its operating point must, therefore, be judiciously chosen to obtain the maximum emitted flux. The guiding of light in matter is made possible by the phenomenon of total internal reflection. Depending on the guide material and its immersive environment, a limiting angle defines whether the ray will be reflected or transmitted.

If this condition is not adhered to, then the light ray escapes. This happens when the curvature is too pronounced or where there are surface defects (roughness, bubbles, etc.).

Conversely, to obtain a uniform light rendering along a guide, a well-designed diffusing surface that disrupts the light guidance properties is required. This makes it possible to extract the light in a pre-planned manner and obtain a uniform light rendering along a guide.  For this purpose, we use the phenomenon of volume extraction (particles in the material) or surface extraction (surface texturing).

The choice of material is also critical. It must take into account the length of the guide, its geometry, and the mechanical constraints linked to the use of the product in which it is integrated (resistance to shocks, UV rays, etc.). Our extensive knowledge of the optical properties of materials, our independent database with relevant references, and our privileged relationships with many compounders  allow us to quickly choose the correct materials, taking into account several criteria such as uniformity, luminance, transmittance according to length, volume diffusion, etc.)

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Our optical design and simulation tools are able to integrate all the parameters mentioned above and thus accurately report the performance achievable by the optical solutions based on light guides developed by PISÉO engineers.

PISÉO experts have fully mastered these principles and are thus able to design the appropriate optical architectures and simulate their visual performance with their tools such as Lighttools or Zemax OpticStudio.

Color mix

HMIs that incorporate a light guide often require the ability to display different colors. In this case, their coupling with colored LEDs, discrete or “packaged” and controlled by appropriate electronics and algorithms, is an excellent way to create a multitude of colors for these devices. However, achieving consistent color results on visible surfaces remains a challenge. In reality, only a specifically designed and carefully studied optical architecture, allowing efficient coupling of LED luminous flux and impeccable color mixing, is capable of producing a superior quality result.

PISÉO’s optical engineers benefit from extensive experience in the design of light guides for color mixing. They know how to take into account the mechanical and aesthetic constraints of the products and the manufacturability of the components to best meet your objectives.

Light guide prototype

Thanks to their network of trusted partners, PISÉO engineers are able to produce prototypes of light guides to validate their design. Like all optical components, to be sufficiently representative, these prototypes must be made with great care. This is why PISÉO offers to manage the entire process.

The light guides are then integrated into a system, allowing the pairing of the light source(s), generally LEDs wired onto printed circuits. The functional assembly is tested in the PISÉO laboratory. Precise measurements of luminous flux, illuminance light distribution, luminance, and colorimetric parameters can thus be carried out to check the prototype’s performance.

If you wish to integrate lighting systems based on efficient and qualitative light guides into your products, be like our many satisfied customers, and do not hesitate to trust the optical engineers at PISÉO.

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Drawing on their skills and the technical means in their laboratory, PISÉO experts can identify the root causes of system failures and propose solutions to improve their reliability.

Electrical failure

An installer of lighting fixtures turned to PISEO because he was confronted with operating failures on ribbons integrating colored light-emitting diodes (LEDs).

The failure noted was that certain segments of these ribbons no longer showed any illumination. After several fruitless searches, our client turned to PISEO’s experts to understand the cause of the problem and to find a solution with the manufacturer of the lighting equipment.

Our experts carried out an analysis of the entire system including LEDs, printed circuits, power supplies, digital multiplex (DMX) control, mechanical construction and heat sink. We verified the operating points of the LED components, and their electrical and thermal measurements. PISEO carried out visual observations with an image magnification device. Our experts were thus able to demonstrate that the malfunction observed was due to the failure of certain LEDs, itself caused by an electrical overvoltage external to the system.

This analysis revealed the probable causes of the failure. At the end of this work, we submitted an independent expert report to the customer.

Failure due to poor design

A distributor of LED lamps and lighting asked us to appraise a lighting device in which a certain number of LEDs were no longer lighting up.

During their analysis, the PISEO experts found that the design of the product did not correspond to the state of the art and involved risks.

Indeed, they were able to observe that by heating, the expansion of the LED printed circuit boards (PCBs) caused mechanical stress. This led to buckling and detachment of the PCBs.

The measurements carried out by thermal camera showed in particular that the chains of LEDs present where the PCB was peeling off also presented abnormally high temperatures, thus leading to the failure of certain LEDs. In this case, the design of the product could be called into question because the solutions implemented by the manufacturer did not take into account the phenomena of expansion of the PCBs during the operation of the product.

Failure of photo-chemical origin

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A swimming pool lighting device manufacturer was confronted with a phenomenon of browning of the silicone coating the LEDs, which ensure the sealing of its products. After consulting the LED manufacturer, who was unable to provide an answer, the product manufacturer turned to PISEO to find the cause of the failure.

During their analysis and in particular the disassembly of several products, the PISEO experts found that the silicone was not always correctly cross-linked and hardened and that it included a seal containing sulphur. However, non-crosslinked silicone exposed to optical radiation and in the presence of sulphur loses its transparency and changes color after a certain time. Thanks to their expertise in materials, optics and design of optronic systems, PISEO’s experts succeeded in identifying the cause of the failure. Our customer was thus able to improve his product and obtain a very significant commercial success internationally.

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