Radio astronomers also use this convention in accordance with an International Astronomical Union (IAU) resolution made in 1973.[8]

I had this thread because I came across this article the other day and began thinking: https://ledlightinginfo.com/can-a-lux-meter-measure-led-light I guess I will just take a grain of salt when dealing with this in the future.

In a circularly polarized electromagnetic wave, the individual electric field vectors, as well as their combined vector, have a constant magnitude, and with changing phase angle. Given that this is a plane wave, each vector represents the magnitude and direction of the electric field for an entire plane that is perpendicular to the optical axis. Specifically, given that this is a circularly polarized plane wave, these vectors indicate that the electric field, from plane to plane, has a constant strength while its direction steadily rotates. Refer to these two images[dead link‍] in the plane wave article to better appreciate this dynamic. This light is considered to be right-hand, clockwise circularly polarized if viewed by the receiver. Since this is an electromagnetic wave, each electric field vector has a corresponding, but not illustrated, magnetic field vector that is at a right angle to the electric field vector and proportional in magnitude to it. As a result, the magnetic field vectors would trace out a second helix if displayed.

FM broadcast radio stations sometimes employ circular polarization to improve signal penetration into buildings and vehicles. It is one example of what the International Telecommunication Union refers to as "mixed polarization", i.e. radio emissions that include both horizontally- and vertically-polarized components.[14] In the United States, Federal Communications Commission regulations state that horizontal polarization is the standard for FM broadcasting, but that "circular or elliptical polarization may be employed if desired".[15]

Circular polarization occurs when the two orthogonal electric field component vectors are of equal magnitude and are out of phase by exactly 90°, or one-quarter wavelength.

The phenomenon of polarization arises as a consequence of the fact that light behaves as a two-dimensional transverse wave.

Note that this principle only holds strictly for light reflected at normal incidence. For instance, right circularly polarized light reflected from a dielectric surface at grazing incidence (an angle beyond the Brewster angle) will still emerge as right-handed, but elliptically polarized. Light reflected by a metal at non-normal incidence will generally have its ellipticity changed as well. Such situations may be solved by decomposing the incident circular (or other) polarization into components of linear polarization parallel and perpendicular to the plane of incidence, commonly denoted p and s respectively. The reflected components in the p and s linear polarizations are found by applying the Fresnel coefficients of reflection, which are generally different for those two linear polarizations. Only in the special case of normal incidence, where there is no distinction between p and s, are the Fresnel coefficients for the two components identical, leading to the above property.

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Note that the IEEE defines RHCP and LHCP the opposite as those used by physicists. The IEEE 1979 Antenna Standard will show RHCP on the South Pole of the Poincare Sphere. The IEEE defines RHCP using the right hand with thumb pointing in the direction of transmit, and the fingers showing the direction of rotation of the E field with time. The rationale for the opposite conventions used by Physicists and Engineers is that Astronomical Observations are always done with the incoming wave traveling toward the observer, where as for most engineers, they are assumed to be standing behind the transmitter watching the wave traveling away from them. This article is not using the IEEE 1979 Antenna Standard and is not using the +t convention typically used in IEEE work.

Just as in the other convention, right-handedness corresponds to a clockwise rotation, and left-handedness corresponds to an anti-clockwise rotation.

The bioluminescence of the larvae of fireflies is also circularly polarized, as reported in 1980 for the species Photuris lucicrescens and Photuris versicolor. For fireflies, it is more difficult to find a microscopic explanation for the polarization, because the left and right lanterns of the larvae were found to emit polarized light of opposite senses. The authors suggest that the light begins with a linear polarization due to inhomogeneities inside aligned photocytes, and it picks up circular polarization while passing through linearly birefringent tissue.[20]

As a specific example, refer to the circularly polarized wave in the first animation. Using this convention, that wave is defined as right-handed because when one points one's right thumb in the same direction of the wave's propagation, the fingers of that hand curl in the same direction of the field's temporal rotation. It is considered clockwise circularly polarized because, from the point of view of the source, looking in the same direction of the wave's propagation, the field rotates in the clockwise direction. The second animation is that of left-handed or anti-clockwise light, using this same convention.

The classical sinusoidal plane wave solution of the electromagnetic wave equation for the electric and magnetic fields is:

"To achieve circular polarization [in axial or end-fire mode] ... the circumference C of the helix must be ... with C/wavelength = 1 near optimum, and the spacing about S = wavelength/4," p.571;

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Circularly polarized light can be converted into linearly polarized light by passing it through a quarter-waveplate. Passing linearly polarized light through a quarter-waveplate with its axes at 45° to its polarization axis will convert it to circular polarization. In fact, this is the most common way of producing circular polarization in practice. Note that passing linearly polarized light through a quarter-waveplate at an angle other than 45° will generally produce elliptical polarization.

David thanks for your insight. Yeah I understand to decide the working stop, it would require a light meter. But I still want to know if I take a Incident reading under LED lights, is that reading still considered valid/trustworthy?

The handedness of polarized light is reversed reflected off a surface at normal incidence. Upon such reflection, the rotation of the plane of polarization of the reflected light is identical to that of the incident field. However, with propagation now in the opposite direction, the same rotation direction that would be described as "right-handed" for the incident beam, is "left-handed" for propagation in the reverse direction, and vice versa. Aside from the reversal of handedness, the ellipticity of polarization is also preserved (except in cases of reflection by a birefringent surface).

where θ l e f t {\displaystyle \theta _{\mathrm {left} }} corresponds to the quantum yield of left-handed circularly polarized light, and θ r i g h t {\displaystyle \theta _{\mathrm {right} }} to that of right-handed light. The maximum absolute value of gem, corresponding to purely left- or right-handed circular polarization, is therefore 2. Meanwhile, the smallest absolute value that gem can achieve, corresponding to linearly polarized or unpolarized light, is zero.

Using this convention, the electric field vector of a left-handed circularly polarized wave is as follows: ( E x , E y , E z ) ∝ ( cos ⁡ 2 π λ ( c t − z ) , − sin ⁡ 2 π λ ( c t − z ) , 0 ) . {\displaystyle \left(E_{x},\,E_{y},\,E_{z}\right)\propto \left(\cos {\frac {2\pi }{\lambda }}\left(ct-z\right),\,-\sin {\frac {2\pi }{\lambda }}\left(ct-z\right),\,0\right).}

When using this convention, in contrast to the other convention, the defined handedness of the wave matches the handedness of the screw type nature of the field in space. Specifically, if one freezes a right-handed wave in time, when one curls the fingers of one's right hand around the helix, the thumb will point in the direction of progression for the helix, given the sense of rotation. Note that, in the context of the nature of all screws and helices, it does not matter in which direction you point your thumb when determining its handedness.

A number of different types of antenna elements can be used to produce circularly polarized (or nearly so) radiation; following Balanis,[16] one can use dipole elements:

The nature of circular polarization and its relationship to other polarizations is often understood by thinking of the electric field as being divided into two components that are perpendicular to each other. The vertical component and its corresponding plane are illustrated in blue, while the horizontal component and its corresponding plane are illustrated in green. Notice that the rightward (relative to the direction of travel) horizontal component leads the vertical component by one quarter of a wavelength, a 90° phase difference. It is this quadrature phase relationship that creates the helix and causes the points of maximum magnitude of the vertical component to correspond with the points of zero magnitude of the horizontal component, and vice versa. The result of this alignment are select vectors, corresponding to the helix, which exactly match the maxima of the vertical and horizontal components.

where the plus sign indicates left circular polarization, and the minus sign indicates right circular polarization. In the case of circular polarization, the electric field vector of constant magnitude rotates in the x-y plane.

As stated earlier, there is significant confusion with regards to these two conventions. As a general rule, the engineering, quantum physics, and radio astronomy communities use the first convention, in which the wave is observed from the point of view of the source.[5][7][8] In many physics textbooks dealing with optics, the second convention is used, in which the light is observed from the point of view of the receiver.[7][9]

In general, this phenomenon will be exhibited in absorption bands of any optically active molecule. As a consequence, circular dichroism is exhibited by most biological molecules, because of the dextrorotary (e.g., some sugars) and levorotary (e.g., some amino acids) molecules they contain. Noteworthy as well is that a secondary structure will also impart a distinct CD to its respective molecules. Therefore, the alpha helix, beta sheet and random coil regions of proteins and the double helix of nucleic acids have CD spectral signatures representative of their structures.

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To appreciate how this quadrature phase shift corresponds to an electric field that rotates while maintaining a constant magnitude, imagine a dot traveling clockwise in a circle. Consider how the vertical and horizontal displacements of the dot, relative to the center of the circle, vary sinusoidally in time and are out of phase by one quarter of a cycle. The displacements are said to be out of phase by one quarter of a cycle because the horizontal maximum displacement (toward the left) is reached one quarter of a cycle before the vertical maximum displacement is reached. Now referring again to the illustration, imagine the center of the circle just described, traveling along the axis from the front to the back. The circling dot will trace out a helix with the displacement toward our viewing left, leading the vertical displacement. Just as the horizontal and vertical displacements of the rotating dot are out of phase by one quarter of a cycle in time, the magnitude of the horizontal and vertical components of the electric field are out of phase by one quarter of a wavelength.

Circular dichroism (CD) is the differential absorption of left- and right-handed circularly polarized light. Circular dichroism is the basis of a form of spectroscopy that can be used to determine the optical isomerism and secondary structure of molecules.

Funnily enough I was just thinking of getting a better meter. I only have an old Sekonic L-398A, and much as it's a classic design, the direct approach of simply connecting a solar panel to a moving-coil voltmeter doesn't work at the sort of low light levels typical of current practice. The aim would be to improve consistency, given I'm more often working on a tiny crew without a dedicated DIT.

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All LEDs are emitting visible wavelengths. And the lightmeters are reading visible wavelengths, too. Hence, I don’t see any problems. (The lightmeters also don’t become inaccurate when you put colored gels in front of your halogen lamps - unless you are using orthochromatic films, infrared films/cameras or sensors that don’t react to certain colors.)

The next pair of illustrations is that of left-handed, counterclockwise circularly polarized light when viewed by the receiver. Because it is left-handed, the rightward (relative to the direction of travel) horizontal component is now lagging the vertical component by one quarter of a wavelength, rather than leading it.

I forgot to mention, what I meant was when these DPs/Gaffers tried to set up a scene or when they do pre-light or just in general maintain lighting consistence from shot to shot, not while shooting, which I believe they can sort of 'eyeball' the exposure. Any thoughts?

In electrodynamics, the strength and direction of an electric field is defined by its electric field vector. In the case of a circularly polarized wave, the tip of the electric field vector, at a given point in space, relates to the phase of the light as it travels through time and space. At any instant of time, the electric field vector of the wave indicates a point on a helix oriented along the direction of propagation. A circularly polarized wave can rotate in one of two possible senses: right-handed circular polarization (RHCP) in which the electric field vector rotates in a right-hand sense with respect to the direction of propagation, and left-handed circular polarization (LHCP) in which the vector rotates in a left-hand sense.

is the angular frequency of the wave; Q = [ x ^ , y ^ ] {\displaystyle \mathbf {Q} =\left[{\hat {\mathbf {x} }},{\hat {\mathbf {y} }}\right]} is an orthogonal 2 × 2 {\displaystyle 2\times 2} matrix whose columns span the transverse x-y plane; and c {\displaystyle c} is the speed of light.

This convention is in conformity with the Institute of Electrical and Electronics Engineers (IEEE) standard and, as a result, it is generally used in the engineering community.[4][5][6]

Water-air interfaces provide another source of circular polarization. Sunlight that gets scattered back up towards the surface is linearly polarized. If this light is then totally internally reflected back down, its vertical component undergoes a phase shift. To an underwater observer looking up, the faint light outside Snell's window therefore is (partially) circularly polarized.[22]

I usually have the DIT grab frames of the master and I then compare my coverage to see if the look has drifted in terms of balance, color, etc. But when lighting the coverage, I usually start by having the lens set to the same f-stop as the master and often I'm not changing the background lights, just the foreground.

"... two crossed dipoles provide the two orthogonal field components.... If the two dipoles are identical, the field intensity of each along zenith ... would be of the same intensity. Also, if the two dipoles were fed with a 90° degree time-phase difference (phase quadrature), the polarization along zenith would be circular.... One way to obtain the 90° time-phase difference between the two orthogonal field components, radiated respectively by the two dipoles, is by feeding one of the two dipoles with a transmission line which is 1/4 wavelength longer or shorter than that of the other," p.80;

Circularly polarized luminescence (CPL) can occur when either a luminophore or an ensemble of luminophores is chiral. The extent to which emissions are polarized is quantified in the same way it is for circular dichroism, in terms of the dissymmetry factor, also sometimes referred to as the anisotropy factor. This value is given by:

Funnily enough I was just thinking of getting a better meter. I only have an old Sekonic L-398A, and much as it's a classic design, the direct approach of simply connecting a solar panel to a moving-coil voltmeter doesn't work at the sort of low light levels typical of current practice. The aim would be to improve consistency, given I'm more often working on a tiny crew without a dedicated DIT.

Also, under the right conditions, even non-chiral molecules will exhibit magnetic circular dichroism — that is, circular dichroism induced by a magnetic field.

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If α y {\displaystyle \alpha _{y}} is rotated by π / 2 {\displaystyle \pi /2} radians with respect to α x {\displaystyle \alpha _{x}} and the x amplitude equals the y amplitude, the wave is circularly polarized. The Jones vector is:

In the quantum mechanical view, light is composed of photons. Polarization is a manifestation of the spin angular momentum of light. More specifically, in quantum mechanics, the direction of spin of a photon is tied to the handedness of the circularly polarized light, and the spin of a beam of photons is similar to the spin of a beam of particles, such as electrons.[17]

Be advised though they will be about 1/10th of a stop off as I believe Sekonic is set to 12% grey (or the Minolta maybe?) Though that's a trivial discrepancy.

Circular polarization may be referred to as right-handed or left-handed, and clockwise or anti-clockwise, depending on the direction in which the electric field vector rotates. Unfortunately, two opposing historical conventions exist.

I hardly use a meter but it's not because I don't think it would be inaccurate under LED lighting, maybe it would under a very narrow wavelength of saturated color. But even if it were inaccurate under that condition, it might be consistently inaccurate, enough to help with matching levels shot to shot.

When determining if the wave is clockwise or anti-clockwise circularly polarized, one again takes the point of view of the receiver and, while looking toward the source, against the direction of propagation, one observes the direction of the field's temporal rotation.

Many optics textbooks use this second convention.[9][10] It is also used by SPIE[11] as well as the International Union of Pure and Applied Chemistry (IUPAC).[12]

Circular polarization is often encountered in the field of optics and, in this section, the electromagnetic wave will be simply referred to as light.

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"... circular and elliptical polarizations can be obtained using various feed arrangements or slight modifications made to the elements.... Circular polarization can be obtained if two orthogonal modes are excited with a 90° time-phase difference between them. This can be accomplished by adjusting the physical dimensions of the patch.... For a square patch element, the easiest way to excite ideally circular polarization is to feed the element at two adjacent edges.... The quadrature phase difference is obtained by feeding the element with a 90° power divider," p.859.

Only a few mechanisms in nature are known to systematically produce circularly polarized light. In 1911, Albert Abraham Michelson discovered that light reflected from the golden scarab beetle Chrysina resplendens is preferentially left-polarized. Since then, circular polarization has been measured in several other scarab beetles such as Chrysina gloriosa,[18] as well as some crustaceans such as the mantis shrimp. In these cases, the underlying mechanism is the molecular-level helicity of the chitinous cuticle.[19]

But for pre-lighting a set before the camera would be there, you would work with a light meter or your gaffer might, at least to get to the base f-stop you hope to use. It's less critical today since digital cameras have a range of ISO settings they can work in.

All I can say is what I've seen from experience, and that experience tells me the light meter I use is always right with LEDs. I haven't run tests but my footage and my false color in editing says it's all good.

However, due to the spike in the blue wavelengths in many products, LEDs might have an impact on the color temperatures. But you would have to check this with a color meter.

My question is as the title suggests, in this era where LED dominates so many lighting scenarios, even those really high-end Hollywood productions, do these light meter, say a Sekonic 858, no long works with these LED lights? I can't imagine Hollywood DPs throw away their light meters and light only with in-camera or monitors' WFM/False color/Zebra etc.

Consider un-polarized light, which consists of electromagnetic waves with an electric field vector, that oscillates in every transverse direction.

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Quantum physicists also use this convention of handedness because it is consistent with their convention of handedness for a particle's spin.[7]

To convert circularly polarized light to the other handedness, one can use a half-waveplate. A half-waveplate shifts a given linear component of light one half of a wavelength relative to its orthogonal linear component.

In this alternative convention, polarization is defined from the point of view of the receiver. Using this convention, left- or right-handedness is determined by pointing one's left or right thumb toward the source, against the direction of propagation, and then matching the curling of one's fingers to the temporal rotation of the field.

Using this convention, polarization is defined from the point of view of the source. When using this convention, left- or right-handedness is determined by pointing one's left or right thumb away from the source, in the same direction that the wave is propagating, and matching the curling of one's fingers to the direction of the temporal rotation of the field at a given point in space. When determining if the wave is clockwise or anti-clockwise circularly polarized, one again takes the point of view of the source, and while looking away from the source and in the same direction of the wave's propagation, one observes the direction of the field's temporal rotation.

In electrodynamics, circular polarization of an electromagnetic wave is a polarization state in which, at each point, the electromagnetic field of the wave has a constant magnitude and is rotating at a constant rate in a plane perpendicular to the direction of the wave.

As for LED lights; I have no qualms about getting light quantity on any format from any light with a meter. However, if I was shooting film with cheaper LEDs I would really want to use a high end color meter as in that particular case (where you can't easily see a final image) the discontinuous spectrum of some LED lights might be problematic if you're going for a neutral color look. If you're going for something "ugly" or "urban" or "rough" then this is much less of a concern (akin to the old days of pure sodium vapor lighting at night)

Yes it works the same, light is light - I have been using my sekonic l398 with my aputure 200d light and it’s just as accurate as when I use it outdoors or really in any other lighting conditions.

Circular polarization is a limiting case of elliptical polarization. The other special case is the easier-to-understand linear polarization. All three terms were coined by Augustin-Jean Fresnel, in a memoir read to the French Academy of Sciences on 9 December 1822.[1][2] Fresnel had first described the case of circular polarization, without yet naming it, in 1821.[3]

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To avoid confusion, it is good practice to specify "as defined from the point of view of the source" or "as defined from the point of view of the receiver" when discussing polarization matters.

Weaker sources of circular polarization in nature include multiple scattering by linear polarizers[dubious – discuss], as in the circular polarization of starlight, and selective absorption by circularly dichroic media.

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