Comparing the two standards and the protective effect mentioned therein of welding safety spectacles and infrared safety spectacles, it quickly becomes clear that IR spectacles are capable of absorbing five to ten times more radiation within the 700 to 2,700 nm spectrum than welding spectacles – while still allowing just as much visual radiation through. Our professional uvex IR-ex infrared safety spectacles therefore provide effective protection when working with both types of radiation, meet both standards (EN 169 and EN 171) and are way ahead of welding spectacles when it comes to the protection that they offer. And, because our IR-ex spectacles also provide protection from UV radiation up to 400 nanometres, the requirements of EN 170 for UV filters are also met. Our IR-ex tint therefore offers multiple types of protection for virtually all hazards posed by optical radiation. This multi-certification allows our infrared spectacles to be used for protection when welding and from solar radiation as well. Conversely, a pair of welding safety spectacles does not provide sufficient protection against infrared!

Protect your eyes and those of your employees when working with infrared radiation: rely on the durability, transparency and colour fidelity of uvex IR-ex safety spectacles! Use the temperature of the radiation source to determine the correct level of protection, and please do not hesitate to contact us if you have any questions. You can contact us by telephone (+49 (0)911 97 36 360), by email (serviceteam@uvex.de) or via our contact form.

Depending on its intensity, proximity and the duration of exposure, infrared radiation can be harmful to the eyes as well as to the skin. The eyes generally react much sooner and are much more sensitive than the skin to the effects of IR radiation, which can be harmful from a certain degree of intensity and exposure. The heat can in fact be beneficial to skin to a certain extent: infrared heat in the form of infrared lamps is used for medical purposes such as treating pain, circulation problems, stiff joints, inflammation etc. However, excessive heat can also cause heat cramps, heat exhaustion, heatstroke and burns.

If you operate in areas with particularly high levels of infrared radiation – right in front of the iron-melting furnace, for instance – heat protection clothing and special heat protection are indispensable.

The Abbe equation for resolution avoids the shortcomings of the Rayleigh criterion and Sparrow limit, but with a more indirect interpretation. The process of imaging a specimen in the microscope can be described by a convolution operation between the illumination and fluorescence emission (or transmitted light) point-spread functions. After being subjected to Fourier transformation (see Figure 3), objects observed in the microscope (whether they are periodic or not) can be uniquely described as a summation of numerous sinusoidal curves having different spatial frequencies. Note that the image of a specimen, present in all conjugate image planes, exists as the Fourier transform in the corresponding aperture planes where higher frequencies represent fine specimen detail and lower frequencies represent coarse details (Figure 3(a)). This point is illustrated with the waveform in objective rear aperture in Figure 3(b). The lower spatial frequencies reside near the center of the aperture, while the frequency progressively increases for regions approaching the edges of the aperture.

Infrared wavelength

The concept of convolution in real space can be readily simplified by examining the equivalent operation in Fourier space. In the latter, the transformed object can be multiplied with the Fourier transform of the point-spread function to yield the Fourier transform of an ideal image lacking noise. After Fourier transformation, the point-spread function describes how efficiently each spatial frequency of the specimen is transferred to the final image. Thus, the Fourier-transformed point-spread function is referred to as the optical transfer function (OTF; see Figure 3(b)). The OTF defines the extent to which spatial frequencies containing information about the specimen are lost, retained, attenuated, or phase-shifted during the imaging process. Spatial frequency information that is lost during imaging cannot be recovered, so one of the primary goals for all forms of microscopy is to acquire the highest frequency range as possible for the specimen. The value of the OTF at each spatial frequency (measured in oscillations per meter) is a useful indicator to describe the contrast that a particular sinusoidal object feature achieves in the final image.

You can find more information on our professional IR products in our online brochure for uvex IR-ex. We also have glare safety spectacles, welding safety spectacles and UV safety spectacles in our range. You can also use our handy tint app to help you to select the correct tint.

Infrared wavelength range in nm

As well as the acute risks posed by overheating, the chronic effects of infrared light on the eyes (damage to lenses and retina) are good reason to wear appropriate personal protective equipment when working with infrared radiation.

In addition to the diffraction phenomenon that occurs with divergent light waves in optical instruments, the process of interference describes the recombination and summation of two or more superimposed wavefronts. Interference of light is perhaps the most ubiquitous phenomenon in optical microscopy and plays a central role in all aspects of image formation. In fluorescence or laser scanning confocal microscopy, the role of the objective is to focus the excitation light onto a focal point in order to ensure constructive interference of the focused wavefront at the specimen plane. In terms of this requirement, constructive interference (discussed below) ensures that the electric field vector of wavefronts incident from all available objective aperture angles resides in the same phase and therefore produces the smallest possible excitation spot.

Although the Rayleigh criterion and similar measures are useful resolution gauges for observation of the specimen, there remain several shortcomings of such a definition for resolution. For example, in cases where the investigator is aware that two particles are merged to form a single point image, computer algorithms can be applied to discriminate between the particles to arbitrarily smaller distances. Determining the exact position of the two adjacent particles then becomes a question of experimental precision dictated by photon statistics rather than being described by the Rayleigh limit. Furthermore, resolution limits do not necessarily correspond to the level of detail that can be observed in images. While the Rayleigh limit is defined as the distance from the center of the first minimum of the point-spread function, this value can be rendered smaller by advanced optical systems or linear optics. Resolution criteria also do not rely on the fact that light is a diffracting wavefront that poses a finite limit to the level of detail that is actually contained within the waves.

Michael W. Davidson - National High Magnetic Field Laboratory, 1800 East Paul Dirac Dr., The Florida State University, Tallahassee, Florida, 32310.

Particular caution is advised in the event of infrared coming into excessively long direct contact with the eyes because its harmful effect on eye health varies depending on how deeply the IR radiation manages to penetrate the eye tissue:

Alternative text: We also have the precise spectacles tint for many other applications, offering you the best protection and comfort for your work. Find out more here: uvex lens tint (uvex-safety.com)

Infrared light

Our infrared safety spectacles feature our proven uvex supravision coating technology to pair top protection with a superbly clear view! Choose from the sporty uvex pheos cx2 and the uvex super f OTG as overspecs for prescription spectacle wearers. Experience the quality of our infrared spectacles for yourself and try out the colour recognition on our uvex IR-ex page!

First of all, welding spectacles and infrared safety spectacles are subject to two different safety standards: while welding spectacles are designed specifically for welding applications and the respective output from the welding machine in accordance with EN 169, infrared safety spectacles are designed in accordance with EN 171; this standard intends for the eye protection to be selected according to the average temperature of the radiating heat source.

Illustrated in Figure 1 is the effect of objective aperture angle on the size of a diffraction spot produced in a typical optical microscope. The point source and its conjugate (P) in the image plane where wavefronts converge and undergo constructive interference are illustrated for objectives having large (Figure 1(a)) and small (Figure 1(b)) numerical aperture. The point P1is moved laterally in the focal plane until destructive interference at a certain distance (dictated by the objective numerical aperture) defines the location of the first diffraction minimum and thus the radius of the diffraction spot. For the high resolution configuration in Figure 1(a), Points A and B in the wavefront produce a smaller spot size with 10 arbitrary units defining the imaged spot size. In contrast, for the lower resolution configuration presented in Figure 1(b), the reduced aperture angle increases the distance between A and B to 18 arbitrary units. In other words, light emitted by a fluorophore (the point source) is focused by the objective at the image plane where wavefronts traveling the same distance arrive at the image plane in phase and interfere constructively to produce a spot having high intensity. Destructive interference, leading to zero intensity, is generated by wavefronts that arrive one-half wavelength out of phase (see discussion above). Because the drop in intensity is gradual along the lateral axis of the spot, two point sources (or fluorescent molecules) closer together than the size of the spot will appear to be a single, larger spot and are unresolved.

A pair of uvex IR-ex spectacles can provide you with optimum protection against the effects of infrared in your workplace. To determine which spectacles have the correct level of protection, establish the average temperature of the source of radiation – i.e. the burning object (such radiation measurements are performed as part of the workplace risk assessment in larger companies). The table provided sets out the official levels of protection of the relevant EN 171 standard and the level of protection that uvex infrared spectacles offer:

Infrared waves

As described above, the intensity distribution of an Airy disk in three dimensions is referred to as a point-spread function and completely describes the diffraction pattern of a point source of light (such as a single fluorophore) in the lateral (x,y) and axial (z) dimensions as modified by a diffraction-limited optical microscope. The size of the point spread function is determined by the wavelength of imaging light and the characteristics of the objective (numerical aperture) and the refractive index of the imaging medium. Resolution, in a practical sense, is often defined as the smallest separation distance between two point-like objects in which they can still be distinguished as individual emitters (and not amalgamated into a single spot). As a result, most resolution criteria (for example, the Rayleigh criterion, Sparrow limit, or the full width at half maximum; FWHM) are directly related to the properties and geometry of the point-spread function.

Infrared dangers

Infrared is radiation with a wavelength between 780 nanometres and one millimetre on the electromagnetic spectrum. This IR radiation cannot be perceived by the naked eye, even if the heat emitted by the radiation can be felt. Particular caution is therefore required when dealing with extremely warm and prolonged radiation. Infrared light is divided into three types depending on the wavelength: IR-A, IR-B and IR-C. The longer the waves of the IR radiation, the less able they are to penetrate fabric or dermal layers. At 780 nm to 1,400 nm, the comparatively short-wave IR-A radiation is therefore the most harmful type in terms of human health (greatest degree of penetration). UV light is also invisible, but its wavelength spectrum is below 400 nm and it therefore has a shorter wavelength than radiation within the visible range of the spectrum.

Presented in Figure 2 is a graphical representation of the Rayleigh criterion for both the lateral and axial dimensions of two closely positioned point sources. In Figure 2(a), the intensity of the point sources is represented by solid blue and dashed yellow curves. The total intensity generated by the combined point sources is represented by a red curve that is displaced along the ordinate for clarity. In order to distinguish between these point sources, the distance between the peaks should be sufficient to produce an intensity minimum that ranges between 20 and 30 percent of the peak intensity (Figure 2(a)). The same criterion applies to the axial dimension (Figure 2(b)). Note that the resolution (indicated in Figures 2(a) and 2(b) along the abscissa) is significantly lower along the z axis.

Aside from the aforementioned situations in people’s personal lives, there are many industrial settings in which infrared radiation is used in a variety of ways. Typical examples include:

According to the Rayleigh criterion, two point sources observed in the microscope are regarded as being resolved when the principal diffraction maximum (the central spot of the Airy disk; see Figure 2) from one of the point sources overlaps with the first minimum (dark region surrounding the central spot) of the Airy disk from the other point source. If the distance between the two Airy disks or point-spread functions is greater than this value, the two point sources are considered to be resolved (and can readily be distinguished). Otherwise, the Airy disks merge together and are considered not to be resolved. Stated in other terms, the Rayleigh criterion is satisfied when the distance between the images of two closely spaced point sources is approximately equal to the width of the point-spread function. In contrast, the Sparrow resolution limit is defined as the distance between two point sources where the images no longer have a dip in brightness between the central peaks, but rather exhibit constant brightness across the region between the peaks. The Sparrow resolution limit is closer to the Abbe value and approximately two-thirds (Equation (4)) of the Rayleigh resolution limit.

All filters of the infrared safety spectacles and of other PPE in this range must meet the transmission requirements of EN 171 and are divided into defined levels of protection accordingly. Standard 166 for general personal eye protection stipulates further requirements for infrared safety spectacles. You can find illustrations and other explanations of these specifications and the applicable standards for safety spectacles on our website.

Infrared radiation, or thermal radiation, was discovered in the year 1800 by Friedrich Wilhelm (William) Herschel, musician and astronomer. Everyday sources of infrared radiation include:

Infrared examples

Even in cases where an optical microscope is equipped with the highest available quality of lens elements, is perfectly aligned, and has the highest numerical aperture, the resolution remains limited to approximately half the wavelength of light in the best case scenario. In practice, the resolution typically achieved in routine imaging often does not reach the physical limit imposed by diffraction. This is due to the fact that optical inhomogeneities in the specimen can distort the phase of the excitation beam, leading to a focal volume that is significantly larger than the diffraction-limited idea. Additionally, resolution can also be compromised by the use of incompatible immersion oil, coverslips having a thickness outside the optimum range, and improperly adjusted correction collars.

Our infrared light spectacles also meet the requirements of U.S. standard ANSI/ISEA Z87.1 and Japanese standard JIS T8141. This multi-certification allows our infrared spectacles to be used for protection when welding and from solar radiation as well. Conversely, a pair of welding safety spectacles does not provide sufficient protection against infrared!

The optical microscope has played a central role in helping to untangle the complex mysteries of biology ever since the seventeenth century when Dutch inventor Antoni van Leeuwenhoek and English scientist Robert Hooke first reported observations using single-lens and compound microscopes, respectively. Over the past three centuries, a vast number of technological developments and manufacturing breakthroughs have led to significantly advanced microscope designs featuring dramatically improved image quality with minimal aberration. However, despite the computer-aided optical design and automated grinding methodology utilized to fabricate modern lens components, glass-based microscopes are still hampered by an ultimate limit in optical resolution that is imposed by the diffraction of visible light wavefronts as they pass through the circular aperture at the rear focal plane of the objective. As a result, the highest achievable point-to-point resolution that can be obtained with an optical microscope is governed by a fundamental set of physical laws that cannot be easily overcome by rational alternations in objective lens or aperture design. These resolution limitations are often referred to as the diffraction barrier, which restricts the ability of optical instruments to distinguish between two objects separated by a lateral distance less than approximately half the wavelength of light used to image the specimen.

Infrared frequency

Whether you work right in front of a furnace in a foundry or a certain distance away, appropriate eye and face protection – plus where necessary the right heat protection clothing – are essential for you to be able to work safely.

Laser scanning confocal and multiphoton microscopy have been widely used to moderately enhance spatial resolution along both the lateral and axial axes, but the techniques remain limited in terms of achieving substantial improvement. The focused laser excitation coupled with pinhole-restricted detection in confocal microscopy can, in principle, improve the spatial resolution by a factor of 1.4, although this is only realized at a significant cost in signal-to-noise. Likewise, multiphoton fluorescence microscopy takes advantage of nonlinear absorption processes to reduce the effective size of the excitation point-spread function. Once again, however, the smaller and more refined point-spread function is counteracted by the necessity to use longer wavelength excitation light. As a result, rather than providing dramatic improvements to resolution, the primary advantage of confocal and multiphoton microscopy over traditional widefield techniques is the reduction of background signal originating from emission sources removed from the focal plane (out-of-focus light), which enables crisp optical sections to be obtained for three-dimensional volume-rendered imaging.

The resolution limits imposed by the physical laws that govern optical microscopy can be exceeded, however, by taking advantage of "loopholes" in the law that underscore the fact that the limitations are true only under certain assumptions. Techniques exploiting these "loopholes" have come to be known as super-resolution microscopies, with many major manufacturers now offering various types of super-resolution microscopes.

The process of diffraction involves the spreading of light waves when they interact with the intricate structures that compose a typical specimen. Due to the fact that most specimens observed in the microscope are composed of highly overlapping features that are best represented by multiple point sources of light, discussions of the microscope diffraction barrier center on describing the passage of wavefronts representing a single point source of light through the various optical elements and aperture diaphragms. As will be discussed below, the transmitted light or fluorescence emission wavefronts emanating from a point in the specimen plane of the microscope become diffracted at the edges of the objective aperture, effectively spreading the wavefronts to produce an image of the point source that is broadened into a diffraction pattern having a central disk of finite, but larger size than the original point. Therefore, due to diffraction of light, the image of a specimen never perfectly represents the real details present in the specimen because there is a lower limit below which the microscope optical system cannot resolve structural details.

Nikon offers a range of super-resolution systems for high-speed imaging applications and single-molecule level imaging needs.

where λ is the average wavelength of illumination in transmitted light or the excitation wavelength band in fluorescence. The objective numerical aperture (NA = n•sin(θ)) is defined by the refractive index of the imaging medium (n; usually air, water, glycerin, or oil) multiplied by the sine of the aperture angle (sin(θ)). As a result of this relationship, the size of the spot created by a point source decreases with decreasing wavelength and increasing numerical aperture, but always remains a disk of finite diameter. Thus, the image spot size produced by a 100x magnification objective having a numerical aperture of 0.90 in green light (550 nanometers) is approximately 300 nanometers, whereas the spot size produced by a 100x objective of numerical aperture 1.4 is approximately 200 nanometers. The diffraction-limited resolution theory was advanced by German physicist Ernst Abbe in 1873 (see Equation (1)) and later refined by Lord Rayleigh in 1896 (Equation (3)) to quantitate the measure of separation necessary between two Airy patterns in order to distinguish them as separate entities.

Infrared uses

According to Abbe's theory, images are composed from an array of diffraction-limited spots having varying intensity that overlap to produce the final result, as described above. Thus, the only mechanism for optimizing spatial resolution and image contrast is to minimize the size of the diffraction-limited spots by decreasing the imaging wavelength, increasing numerical aperture, or using an imaging medium having a larger refractive index. However, under ideal conditions with the most powerful objectives, lateral resolution is still limited to relatively modest levels approaching 200 to 250 nanometers (see Equation (1)) due to transmission characterics of glass at wavelengths beneath 400 nanometers and the physical constraints on numerical aperture. In contrast, the axial dimension of the Airy disk forms an elliptical pattern that often referred to as the point-spread function (PSF). The elongated geometry of the point-spread function along the optical axis arises from the nature of the non-symmetrical wavefront that emerges from the microscope objective. Axial resolution in optical microscopy is even worse than lateral resolution (as outlined in Equation (2)), on the order of 500 nanometers. When attempting to image highly convoluted features, such as cellular organelles, diffraction-limited resolution is manifested as poor axial sectioning capability and lowered contrast in the imaging plane. Furthermore, overall specimen contrast achieved in three-dimensional specimens is generally dominated by the relatively poor axial resolution that occurs due to out-of-focus light interference with the point-spread function.

In the infrared light risk assessment for your workplace (for eyes and skin), your distance from the source of radiation and the amount of time spent in front of the radiation source are also relevant in determining the strength of your IR radiation exposure.

Both interference and diffraction, which are actually manifestations of the same process, are responsible for creating a real image of the specimen at the intermediate image plane in a microscope. In brief, interference between two wavefronts occurs with addition to double the amplitude if the waves are perfectly in phase (constructive interference), but the waves cancel each other completely when out of phase by 180 degrees (termed destructiveinterference; however, most interference occurs somewhere in between). The photon energy inherent in a light wave is not itself doubled or annihilated when two waves interfere; rather this energy is channeled during diffraction and interference in directions that permit constructive interference. Therefore, interference and diffraction should be considered as phenomena involving the redistribution of light waves and photon energy.

A traditional widefield microscope generates an image of a point source by capturing the light in various locations in the objective and further processing the wavefronts as the pass through the optical train to finally interfere at the image plane. As a consequence of the reciprocity principle in optics, the Abbe limit in the lateral axis of the microscope corresponds to the maximum-to-maximum distance that can be obtained by interfering two waves at the most extreme angles captured by the objective. The Abbe resolution limit is attractive because it depends only on the maximal relative angle between different wavefronts leaving the specimen and captured by the objective. This limit therefore describes the smallest level of detail that can possibly be imaged, and that periodic structures have higher spatial frequency (shorter wavelengths) will not be transferred to the image.

One of the important points to remember about the optical microscope is that the detection optical transfer function has a characteristic frequency that serves as a resolution "cut-off" border (the Abbe limiting frequency; see Figure 3(b)). Frequencies higher than the limiting value are not present in the image recorded by the microscope. The peak-to-peak distance for the highest spatial frequency able to pass through the objective (the value d for the green waveform in Figure 3(a)) is therefore commonly referred to as the Abbe limit, which is more formally defined as the smallest periodicity in a structure that can be detected in the final image. Due to the fact that a point source emits or transmits a wide range of spatial frequencies, the Abbe limit must also be present in the point-spread function spanning three dimensions.

For workplaces where less-intense heat sources do not pose an immediate threat but lasting exposure to infrared poses a hazard, uvex has developed a special range of safety spectacles to provide protection from IR radiation: uvex IR-ex. Combining safety with a clear view, these safety spectacles have the following impressive properties:

A point object in a microscope, such as a fluorescent protein single molecule, generates an image at the intermediate plane that consists of a diffraction pattern created by the action of interference. When highly magnified, the diffraction pattern of the point object is observed to consist of a central spot (diffraction disk) surrounded by a series of diffraction rings (see Figure 1). In the nomenclature associated with diffraction theory, the bright central region is referred to as the zeroth-order diffraction spot while the rings are called the first, second, third, etc., order diffraction rings. When the microscope is properly focused, the intensity of light at the minima between the rings is zero. Combined, this point source diffraction pattern is referred to as an Airy disk (after Sir George B. Airy, a nineteenth century English astronomer). The size of the central spot in the Airy pattern is related to the wavelength of light and the aperture angle of the objective. For a microscope objective, the aperture angle is described by the numerical aperture (NA), which includes the term sin θ, the half angle over which the objective can gather light from the specimen. In terms of resolution, the radius of the diffraction Airy disk in the lateral (x,y) image plane is defined by the following formula:

In professional settings, employees working in glass production and the processing of metals or plastics are among those exposed to the potentially harmful effects of infrared radiation, which is invisible to the naked eye. This article will set out the dangers posed by infrared, list the areas in which IR radiation is found and provide clarification on effective measures to tackle the problem.

When it comes to the long-term dangers posed by infrared radiation, the key question is how to provide employees with effective, reliable protection to keep them healthy while they work.