JP3174145B2 - Lighting equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lighting device having a dimming function for dimming irradiation light from a light source with a liquid crystal element whose transmittance changes according to an applied voltage.

[0002]

2. Description of the Related Art A so-called twisted nematic (T)
Since the N) type liquid crystal element requires a polarizer, it is difficult to increase the luminance. In addition, when the TN type liquid crystal element is used as a dimming element of a lighting device using a large amount of light source. However, there is a problem that heat generation due to the absorption of the polarizer is inevitable.

On the other hand, a structure in which a liquid crystal material is filled in continuous pores of a carrier film made of a transparent matrix such as a polymer having a sponge-like porous structure, or a carrier film made of a transparent matrix is used. The above problem can be solved because a liquid crystal element in which a composite film in which a liquid crystal material is dispersed in a granular manner is sandwiched between a pair of transparent electrodes does not require a polarizer.

In the above liquid crystal element, when no voltage is applied,
Since the liquid crystal molecules are in a random state due to the shape regulation (interface action) of the interface between the liquid crystal molecule and the transparent matrix, the incident light is scattered and the composite film is in an opaque state. . When a voltage is applied between a pair of transparent electrodes sandwiching the composite film, liquid crystal molecules having a positive dielectric anisotropy (Δε) are oriented in an electric field direction according to the magnitude of the applied voltage. Then, the disorder of the arrangement is gradually eliminated, the light transmittance increases, and finally the transparent state is reached.

A liquid crystal material having a nematic phase is usually used for the liquid crystal device having the above-described structure. Further, the spectrum of the transmitted light of the liquid crystal element in the opaque state where no voltage is applied can be controlled by the size and distribution of the holes filled with liquid crystal molecules, the optical properties of each material, and the like.

[0006]

However, the liquid crystal device using the nematic liquid crystal cannot control the spectrum of the transmitted light when a voltage is applied.
In particular, there is a problem that the spectrum of the transmitted light greatly fluctuates in the voltage range until the entire visible light reaches the saturated transmittance.

That is, in the above liquid crystal element, the relationship between the transmittance of light of each wavelength and the applied voltage is not constant in the voltage range until the entire visible light region reaches the saturation transmittance, and the transmittance at the same voltage is equal to the wavelength. In particular, the transmittance of light on the long wavelength side becomes larger than the transmittance of light on the short wavelength side, and the spectrum of the transmitted light greatly shifts to the long wavelength side. Further, since the ratio of the transmittance of each wavelength changes according to the applied voltage, the color tone of the transmitted light changes with the change of the transmittance.

[0008] When the above-mentioned causes were examined, the following became clear. That is, when a voltage is applied to a liquid crystal element using a liquid crystal material exhibiting a nematic phase, the liquid crystal molecules are oriented in the direction of the electric field as described above, but the electric field strength is maintained in the voltage range until the entire visible light region reaches the saturation transmittance. Is not sufficient, the alignment of the liquid crystal molecules is maintained in the vicinity of the interface between the liquid crystal molecules and the transparent matrix due to the interfacial action. For this reason, in the region near this interface, short-wavelength light is mainly scattered, and its transmittance becomes lower than the transmittance of long-wavelength light, and the transmitted light shows a spectrum in which the long-wavelength side is dominant. .

The wavelength of light and the extent to which the light is scattered are determined by the degree of discontinuity of the orientation of the liquid crystal molecules (the size of the region in which the orientation of the liquid crystal molecules is disturbed, the degree of disturbance of the liquid crystal molecules in the above-mentioned region). Etc.), and the degree of the discontinuity of the orientation corresponds to the force relationship between the applied voltage and the interfacial effect.
The ratio of the transmittance of each wavelength changes according to the applied voltage, and the color tone of the transmitted light changes.

For this reason, when a conventional liquid crystal element using a normal liquid crystal material exhibiting a nematic phase is used for OA equipment, AV equipment, etc., there is a problem that the color tone of the display changes unnaturally. When used as a dimming element of a lighting device, it is not possible to obtain dimming light in which the short wavelength side is dominant, dimming light having no wavelength dependence (that is, white), and to keep the color tone of the dimming light constant. There is a problem that can not be.

Therefore, the above-mentioned liquid crystal element has already been used for display or the like by switching between an opaque state and a transparent state in two stages. However, a display element utilizing an intermediate transmission state, a light transmittance, etc. Currently, it is not yet practically used, although it is expected that the dimming element and the like which can adjust the light intensity in multiple steps can be used. The present invention has been made in view of the above circumstances, and it is possible to freely set a spectral distribution of transmitted light when no voltage is applied and in a voltage range until the entire visible light reaches a saturated transmittance. It is an object of the present invention to provide a lighting device that is capable of not changing the color tone of transmitted light unnaturally in accordance with an applied voltage and changing the color tone depending on the degree of dimming, that is, having high color rendering properties.

[0012]

In order to solve the above problems, the present inventors have conducted various studies on liquid crystal materials used for a composite film, and as a result, if a liquid crystal material exhibiting a cholesteric phase is used. It has been found that the influence of the interfacial action can be reduced. That is, in the cholesteric phase, the scattering state at the time of no voltage is caused not only by the above-mentioned interfacial effect but also by the selective scattering and selective reflection effect depending on the chiral pitch, and the occurrence of a defective site due to the irregular arrangement of the liquid crystal molecules. It is considered that the generated scattering wavelength ranges are different based on the respective phenomena, and the electric field values for eliminating the scattering state due to the respective phenomena are different.

For this reason, by controlling factors other than the interfacial effect such as the selective scattering effect so as to cancel out the fluctuation of the transmittance due to the interfacial effect, the spectral distribution of the transmitted light can be freely set, and An illumination device with high color rendering properties in which the color tone of the transmitted light does not change according to the applied voltage can be obtained. Therefore, in the lighting device of the present invention, a light source and a liquid crystal material exhibiting a cholesteric phase having a selective scattering effect of twisted orientation are held in a carrier film made of a transparent matrix, which is arranged on an optical path of light projected from the light source. Comprising a liquid crystal element sandwiching the composite film between a pair of transparent electrodes, in an applied voltage range until the entire visible light region reaches a saturated transmittance, and in an opaque scattering state when no voltage is applied,
In a lighting device in which the transmittance of light in the short wavelength region of the liquid crystal element is equal to or greater than the transmittance of light in the long wavelength region, the liquid crystal material showing the cholesteric phase may be a chiral liquid crystal material that is a nematic phase. While using chiral nematic liquid crystal to which the component was added,
It is characterized in that the dependency of the spectrum of light passing through the composite film on the applied voltage is controlled by adjusting the concentration of the chiral component in the liquid crystal material.

In order to control the distribution of the spectrum of light transmitted through the composite film, the physical properties of the liquid crystal material such as the elastic modulus, average refractive index, and refractive index anisotropy are adjusted, or the physical properties of the carrier film and the fine It is conceivable to adjust the size, shape, film thickness, etc. of the pores.In particular, as a liquid crystal material showing a cholesteric phase, a chiral nematic liquid crystal obtained by adding a chiral component to a liquid crystal material showing a nematic phase is used. It is preferable to adjust the concentration of the chiral component in the material to change the helical arrangement of the liquid crystal molecules. According to the above method, it is possible to set the spectral distribution of the transmitted light by controlling the dependence of the spectrum of the light transmitted through the composite membrane on the applied voltage by simply adjusting the amount of the chiral component added. It becomes possible.

[0015]

[0016]

[0017]

As shown in FIG. 1, a liquid crystal element L constituting a lighting device of the present invention comprises a composite film 1 comprising a pair of transparent electrodes 2 and
It is constituted by pinching with 2. As the transparent electrodes 2 and 2, a transparent support such as glass or a plastic filter (eg, polyethylene terephthalate (PET), polyethersulfone (PES)) or the like is provided on the surface of a transparent support such as ITO (indium tin oxide) or SnO ₂ . In addition to a conductive film formed by a vapor deposition method, a sputtering method, a coating method, or the like, a transparent conductive glass or a filter used for a normal liquid crystal panel can also be used.

As the composite film 1, as shown in FIG. 2, a structure in which a liquid crystal material 12 is filled in continuous holes of a carrier film 11 made of a transparent matrix having a sponge-like structure is preferably employed. Alternatively, a structure in which a liquid crystal material is dispersed in a carrier film formed of a transparent matrix may be employed. In the composite film having the former structure, when the transparent matrix is composed of a polymer, a coating solution in which the polymer and a liquid crystal material are dissolved or dispersed in an appropriate solvent is applied to one transparent electrode 2.
The liquid crystal material is formed by applying a liquid to the surface of the liquid crystal and evaporating the solvent to cause phase separation between the polymer and the liquid crystal material. Thereafter, the other transparent electrode 2 is overlaid on the surface of the formed composite film 1, whereby the liquid crystal element shown in FIG. 1 is completed.

The composite film having the latter structure is formed by a suspension method or a polymerization phase separation method. In the suspension method, the composite film is formed by applying a milky solution obtained by mixing a hydrophilic polymer such as polyvinyl alcohol and a liquid crystal material onto the surface of one of the transparent electrodes 2 and evaporating water in the solution to form a high-concentration solution. It is formed by dispersing a liquid crystal material into molecules in a molecule. Thereafter, the other transparent electrode 2 is overlaid on the surface of the formed composite film 1, whereby the liquid crystal element shown in FIG. 1 is completed.

In the polymerization phase separation method, the liquid crystal element shown in FIG. 1 is prepared by mixing a solution in which a polymer or a polymer precursor (prepolymer), a liquid crystal material and a polymerization initiator are mixed with each other.
The liquid crystal material is injected between the transparent electrodes 2 and 2 and polymerized and cross-linked by ultraviolet light or heat to form a liquid crystal material dispersed in a polymer. The thickness of the composite film must be equal to or longer than the wavelength of visible light in order to form a light-scattering liquid crystal element. However, when the thickness is too large, there is a problem that the driving voltage of the element becomes too high. Therefore, in practice, about 10 to 30 μm is appropriate.

The composite film may contain various known dichroic dyes in order to make the liquid crystal element a color display type. As the liquid crystal material that composes the composite film,
Itself shows a cholesteric phase, a cholesterol compound represented by the following general formula (1), a cholestanol compound represented by the following general formula (2), a β-sitosterol compound represented by the following general formula (3), etc. A conventionally known cholesteric liquid crystal material [“Liquid Crystal Material” published by Kodansha, edited by Shigekazu Sobayashi (1
992) p. 76] can be used, but as described above, a conventionally known liquid crystal material exhibiting a nematic phase (“Liquid Crystal Device Handbook”, published by Nikkan Kogyo Shimbun (1)
989) p. 116-] to which a chiral component is added is suitably used.

[0023]

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(RO- in the above general formulas (1) to (3) represents any of the following formulas R1 to R4)

[0025]

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As the liquid crystal material exhibiting a nematic phase, azomethyl compounds represented by the following general formulas (4) to (6), ester compounds represented by the following general formulas (7) to (10), 11)-biphenyl compounds represented by (13), terphenyl compounds, stilbene compounds represented by the following general formula (14), azoxy compounds represented by the following general formulas (15) and (16), the following general formula ( And azo compounds represented by 17). In addition, pyrimidine compounds such as the following general formulas (18) and (19),
A dioxane compound represented by the general formula (20), a tolan compound represented by the general formula (21), a pyridine compound represented by the general formula (22), and the like can also be used.

[0027]

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[0028]

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[0029]

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[0030]

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[0031]

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[0032]

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(R, R ', R _{1 to} R ₆ ,
X, Y _{are, -C n H 2n + 1,} -OC n H 2n +1, halogen atom, -CN, -OCF _3, represents a substituent of -CF ₃ and the like. The chiral components added to the liquid crystal material include the following formulas (23) to (27):

[0034]

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(In each of the above formulas,

[0036]

[Outside 1]

Represents an asymmetric carbon atom. In addition to the conventionally known chiral molecules such as the compounds represented by the formula (1), various cholesteric liquid crystal materials exemplified above can also be used. The concentration of the chiral component in the liquid crystal material is not particularly limited in the present invention, and may vary depending on conditions such as the type of the chiral component, the type of the liquid crystal material exhibiting a nematic phase, the structure of the composite film, and the operating environment of the liquid crystal element. In such a range that the dependence of the spectrum of light transmitted through the composite film on the applied voltage can be controlled so that the transmittance of light in the wavelength region is equal to or greater than the transmittance of light in the long wavelength region, The concentration is determined.

Although the liquid crystal material is not particularly limited,
It is preferable to use one having a large refractive index anisotropy Δη and a large dielectric anisotropy Δε in order to obtain good characteristics. As the matrix polymer constituting the carrier film together with the liquid crystal material, those having high transparency to visible light are preferable,
For example, a (meth) acrylic polymer represented by PMMA, an epoxy resin, a urethane resin, or the like is suitably used.

The transparent matrix is not limited to a polymer, but may be made of a transparent inorganic material such as glass.
In the driving method of the present invention for driving the liquid crystal element, the effective voltage value is maintained at a value lower than the threshold voltage value for a predetermined period, and the voltage waveform including a component for eliminating the history dependence of the liquid crystal molecules is included. Is applied between the transparent electrodes of the liquid crystal element. More specifically, for example, as shown in FIG. 3 (a), in the voltage waveform (rectangular wave in the figure), or include components only time the voltage 0 t _1, or, shown in FIG. (B) as such, the only time t _1, the applied voltage including a low waveform components effective voltage value than the threshold voltage value is being applied between the transparent electrodes of the liquid crystal element.

The threshold voltage value is a voltage at which the transmittance of the composite film rapidly changes when the voltage applied between the transparent electrodes of the liquid crystal element is gradually increased from 0V.
However, even when the applied voltage is lower than the threshold voltage value, the transmittance of the composite film slightly changes. For example, when the applied voltage is gradually decreased from a sufficiently high voltage, the transmittance of the composite film is reduced. An effective voltage value that becomes 10% may be defined as a threshold voltage value.

If the time t _{1 in} FIGS. 3A and 3B is too long, the decrease in the transmittance of the composite film may be perceived as flickering. Since the hysteresis characteristics may not be sufficiently eliminated and the hysteresis characteristics may remain, it is preferable to set an appropriate value in consideration of the element configuration and the like. Range of the time t ₁ is not particularly limited in the present invention is preferably about 0.5 to 50 milliseconds.

The duration of the time t ₁ may be inserted repeatedly at regular time intervals during the voltage waveform, also when changing the control voltage, even if the circuit adapted to be inserted automatically Good. Next, FIG. 4 shows an example of a lighting device according to the present invention using the above-described liquid crystal element. The illustrated lighting device includes a light source lamp P and a projection optical system S for projecting light from the light source lamp P, and the liquid crystal element L is arranged between the light source lamp P and the projection optical system S. It is composed of Further, a power supply device D for driving is connected to the liquid crystal element L.

The projection optical system S removes components scattered by liquid crystal molecules from the light transmitted through the liquid crystal element L, extracts only the components that have passed straight through the liquid crystal element L, and projects the extracted components on an object to be irradiated. Lens S1, aperture S
2 and the concave lens S3 are arranged on the optical path of the projection light from the light source lamp P with their optical axes aligned.

In the above configuration, since the liquid crystal element L is disposed immediately before the light source lamp P, it is expected that the temperature of the liquid crystal element L will rise due to heat from the light source lamp P when the apparatus is used. You. Therefore, when the liquid crystal element L is used in the illumination device having the configuration shown in the drawing, it is desirable to adjust the characteristics of the element so that the liquid crystal element L operates normally in a heated state. Further, it is possible to protect the liquid crystal element by providing a dielectric multilayer film that reflects ultraviolet light, infrared light, or both on the front surface of the liquid crystal element.

To increase the contrast, the liquid crystal element L
May be laminated and used.

[0046]

The present invention will be described below based on examples and comparative examples. Examples 1 to 3 Nematic liquid crystal material (product number E6 manufactured by Merck Japan Ltd.)
3) and a chiral component (Part No. CB15 manufactured by BDH) were mixed at the compounding ratio shown in Table 1 below to prepare a chiral nematic liquid crystal material, and 75 parts by weight of the chiral nematic liquid crystal material and an acrylic polymer (Made by Teikoku Chemical Co., Ltd.)
25 parts by weight were dissolved in dichloromethane as a solvent so that the solute concentration became 20% to prepare a coating solution.

Next, this coating solution is applied on a glass substrate on which a transparent conductive film is formed by a bar coating method.
The solvent was evaporated in air at atmospheric pressure to form a 18 μm thick composite film. Then, a glass substrate on which the same transparent conductive film as described above is formed is superimposed on the composite film, and about 1 kgf /
A liquid crystal element was manufactured by pressing with a pressure of cm ² and closely contacting each other.

Comparative Example 1 A liquid crystal element was manufactured in the same manner as in Examples 1 to 3 except that the chiral component was not blended.

[0049]

[Table 1]

The following tests were performed on the liquid crystal elements of the above Examples and Comparative Examples to evaluate the performance. Transmittance Characteristic Test I With the liquid crystal devices of the examples and comparative examples set on a spectrophotometer (model number UV-160 manufactured by Shimadzu Corporation), a rectangular wave voltage of 200 Hz was applied between both transparent electrodes, and 400 n
The relationship between the transmittance of light of each wavelength of m, 500 nm, 600 nm and 700 nm and the applied voltage was measured. The applied voltage was increased stepwise from 0 V in steps of 2 V.

FIG. 5 shows the result of Example 1, FIG. 6 shows the result of Example 2, FIG. 7 shows the result of Example 3, and FIG.
8 are shown in FIG. Note that the vertical axis in each of the above figures shows a value obtained by correcting the transmittance of the glass substrate to 100%, and the voltage value on the horizontal axis shows the voltage peak value of the rectangular wave voltage. From the results of these figures, it can be seen that as the concentration of the chiral component in the liquid crystal material increases, the transmittance of light on the short wavelength side increases, and the applied voltage-transmittance characteristic curve of light of each wavelength approaches, and the applied voltage increases. It was found that the color tone did not change according to the color.

From the result of the above measurement, it was found that the wavelength was 400 nm.
Transmittance t ₆₀₀ of the transmittance t ₄₀₀ and the wavelength 600nm light light
And the ratio t ₄₀₀ / t ₆₀₀ was determined, and the relationship with the transmittance of light having a wavelength of 500 nm was plotted. FIG. 9 shows the results. In the figure, the number on the vertical axis is t ₄₀₀ / t ₆₀₀ =
1, and as greater than t ₄₀₀ / t ₆₀₀ is 1 (i.e. large light transmittance at a wavelength of 400 nm), the transmitted light is blue is strong, t ₄₀₀ / t _{60 0} is smaller than 1 (i.e. wavelength 6
The greater the transmittance of light of 00 nm), the stronger the red color.

From the results shown in the figure, it was found that Comparative Example 1 containing no chiral component always had red transmitted light, and Example 1 containing a small amount of chiral component showed similar results. On the other hand, it was found that in Example 2, the transmitted light always showed white, and in Example 3, it became blue. Transmittance Characteristics Test II With the liquid crystal element of Example 2 set on a spectrophotometer (model number UV-160, manufactured by Shimadzu Corporation), the voltage applied between the transparent electrodes was changed stepwise from 0 V to 2 V. 500 when the voltage is increased and when the voltage is decreased in steps of 2V
The change in the transmittance of light having a wavelength of nm was measured. Figure 10 (a), the square wave (frequency 200Hz including middle t _a (= 20 ms) of time corresponding component of the voltage 0, t _b = 8
FIG. 12 shows the result when a voltage of 0 ms was applied.
FIG. 11 shows the results when a simple rectangular wave (frequency 200 Hz) voltage shown in FIG. In addition,
The vertical axis of FIG. 11 shows a value obtained by correcting the transmittance of the glass substrate to 100%, the vertical axis of FIG. 12 shows a value including the transmittance of the glass substrate, and the voltage value of the horizontal axis represents the rectangular wave voltage. The voltage peak value α is shown.

From the results shown in the figure, when a simple rectangular wave was applied, a hysteresis characteristic appeared in the applied voltage-transmittance characteristic at the time of step-up and step-down. However, FIG. When a voltage with the waveform shown in (b) is applied,
The applied voltage and the transmittance could be made to correspond one-to-one during the step-up and the step-down.

[0055]

As described above, the lighting device of the present invention can freely set the spectral distribution of transmitted light when no voltage is applied and in the voltage range until the entire visible light reaches the saturated transmittance. Besides, it is possible to provide an illumination device in which the color tone of the transmitted light does not unnaturally change according to the applied voltage, and the color tone does not change depending on the degree of dimming, that is, high color rendering properties. Therefore, it is possible to obtain dimming light in which the short wavelength side is dominant or dimming light having no wavelength dependency (that is, white), and since the color tone does not change depending on the degree of dimming, various types of illumination and indoor lighting can be obtained. ,
It has a high possibility of being used as a lighting device with a dimming function in a projection television receiver, a projector, a slide projector and the like.

[0056]

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating an example of a layer configuration of a liquid crystal element included in a lighting device of the present invention.

FIG. 2 is an enlarged sectional view of a composite film portion of the liquid crystal element.

FIG. 3A is a waveform chart showing an example of a waveform of an applied voltage in a method of driving a liquid crystal element, and FIG. 3B is a waveform chart showing another example.

FIG. 4 is a conceptual diagram showing an example of the lighting device of the present invention.

FIG. 5 is a graph showing the relationship between the applied voltage and the transmittance of light of each wavelength in the liquid crystal element of Example 1.

FIG. 6 is a graph showing the relationship between the applied voltage and the transmittance of light of each wavelength in the liquid crystal element of Example 2.

FIG. 7 is a graph showing the relationship between the applied voltage and the transmittance of light of each wavelength in the liquid crystal element of Example 3.

FIG. 8 is a graph showing the relationship between the applied voltage and the transmittance of light of each wavelength in the liquid crystal element of Comparative Example 1.

FIG. 9 is a graph showing the relationship between the transmittance and the color tone of the transmitted light in the liquid crystal elements of the above Examples and Comparative Examples.

10A is a waveform diagram showing a waveform of an applied voltage according to a method of driving a liquid crystal element, and FIG. 10B is a waveform diagram showing a normal rectangular wave.

FIG. 11 is a graph showing a relationship between an applied voltage and transmittance when the rectangular wave of FIG. 10B is applied to the liquid crystal element of Example 2.

FIG. 12 shows the applied voltage having the waveform shown in FIG.
7 is a graph showing a relationship between an applied voltage and transmittance when applied to the liquid crystal element of FIG.

[Explanation of symbols]

 L Liquid crystal element 1 Composite film 11 Carrier film 12 Liquid crystal material 2 Transparent electrode P Light source lamp

Continued on the front page (72) Inventor Morihiko Katsuta 1-3-1 Shimaya, Konohana-ku, Osaka City Sumitomo Electric Industries, Ltd. Osaka Works (72) Inventor Toru Kashiwagi 1-3-1 Shimaya, Konohana-ku, Osaka Sumitomo Electric (56) References JP-A-4-119320 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02F 1/1334 G02F 1/137

Claims (1)

(57) [Claims] 1. A composite film comprising a light source and a liquid crystal material having a cholesteric phase having a selective scattering effect of torsional orientation in a carrier film composed of a transparent matrix and arranged on an optical path of light projected from the light source. A liquid crystal element sandwiched between a pair of transparent electrodes, wherein the liquid crystal element is short-circuited in an applied voltage range until the entire visible light reaches a saturated transmittance, and in an opaque scattering state when no voltage is applied. In a lighting device having a transmittance of light in a wavelength region equal to or greater than a transmittance of light in a long wavelength region, the liquid crystal material having a cholesteric phase is a chiral liquid crystal material having a nematic phase and a chiral component added thereto. Using a nematic liquid crystal and adjusting the concentration of the chiral component in the liquid crystal material, the applied voltage of the spectrum of light transmitted through the composite film Lighting apparatus being characterized in that to control the dependence of.