TW201331509A - Use of a light-diffusing polycarbonate sheet as a light cover - Google Patents

Abstract

The present invention therefore provides for the use of a light-diffusing polycarbonate sheet based on a composition comprising (A) 99.9 to 80% by weight of polycarbonate and (B) 0.1 to 20% by weight of diffusing pigment selected from at least one from the group of the silicone resins and the acrylate resins as a light cover, preferably in LED light applications.

Description

Light diffusion polycarbonate sheet for use as a photomask

The present invention relates to the use of a light diffusing polycarbonate sheet as a lampshade, preferably in an LED lighting application, such as an LED lamp or an LED lamp panel, and with respect to a lighting unit comprising the light diffusing polycarbonate panel, preferably It is an LED lighting application (lighting unit with LED as the light source).

The prior art has disclosed light diffusing products composed of transparent polymers having various light diffusing additives and molded articles produced therefrom.

WO 2007/039130 and WO 2007/039131 describe PC compositions having a technical polymer (Techpolymer) as a diffusion pigment.

JP 05257002 describes a light diffusing PC board having a diffusion pigment composed of cerium oxide.

JP 10046022 describes a PC board having a diffusion pigment composed of polyorganodecane.

JP 08220311 describes a two-layer sheet having a diffusing agent coextruded layer of 5 to 25 μm, which comprises an acrylic diffusion pigment, and the diffusion pigment used therefor has a size of 0.1 to 20 μm.

JP 10046018 claims a polycarbonate containing 0.01 to 1% crosslinked polyacrylate spheres.

JP 2004/029091 describes a PC diffuser comprising 0.3 to 20% of a diffusing pigment and 0.0005 to 0.1% of an optical brightener.

US 2004/0066645 A1 request (in general terms) includes A light diffusing material of 0.2 to 5% of light diffusing particles having a light transmittance of more than 70% and a haze of at least 10%, the diffusion additive having an average particle diameter of 3 to 10 μm.

JP 07-090167 claims a light-diffusing polymer composed of 1 to 10% of particles having a refractive index of less than 1.5 and a particle diameter of 1 to 50 μm; and 90 to 99% of an aromatic polycarbonate, Where the particles are substantially insoluble in the aromatic polycarbonate. The diffusion additives used are acrylate, polystyrene, glass, titanium dioxide or calcium carbonate particles.

EP 0 269 324 B1 describes diffusion-additive compositions and light-diffusing thermoplastic polymer compositions comprising from 0.1 to 10% of diffusion additives.

In EP 0 634 445 B1, Paraloid EXL 5137 as a diffusion additive is combined with inorganic particles in polycarbonate (among other materials), and 0.001 to 0.3% of these particles, such as titanium dioxide, have an anti-aging property. Those who contribute and therefore have color stability.

JP 2004-053998 describes a light diffusing polycarbonate film having a thickness of 30 to 200 μm, which is composed of more than 90% of polycarbonate, having a light transmittance of more than 90%, at least one of the surface of the film The side has a textured structure and has a haze of at least 50% and a retardation of less than 30 nm. One use for requesting these optical films is as a diffusion film in a backlight unit. This application describes and requests diffusion films with low birefringence (phase difference <30 nm, better even <20 nm) because they achieve higher brightness in the BLU. The diffusion additives used are from 1 to 10% of inorganic particles, such as cerium oxide, carbonic acid Calcium or talc, or organic particles, such as acrylate or polystyrene having an average diameter of from 1 to 25 μm (preferably from 2 to 20 μm).

JP 08-146207 describes an optical diffusion film in which the surface has been rendered by at least one side by shaping, and additionally requires a film in which only a transparent diffusion additive has been used and which is unevenly distributed The thickness of the film. If two or more diffusion additives are used, they are evenly distributed over the thickness of the film. In the case of uneven distribution of the diffusion additive, thickening occurs at the surface of the film. The diffusion additives used may be acrylate, polyethylene, polypropylene, polystyrene, glass, aluminum or cerium oxide particles having an average particle diameter of 1 to 25 μm. The film may have a thickness of 100 to 500 μm.

JP 2004-272189 describes an optical diffuser having a thickness of 0.3 to 3 mm, and using a diffusion additive having a particle diameter of 1 to 50 μm, which additionally requires a luminance difference of 5,000 to 6000 Cd/m ² to be less than 3%. .

WO 2004/090587 describes a diffusion film for LCDs having a thickness of 20 to 200 μm, which comprises 0.2 to 10% of a diffusion additive, and which has an intensity of 20 to 70% on at least one side. The diffusion additive having a particle size of 5 to 30 μm and crosslinked by a composite bond is polyfluorene oxide, acrylic acid or talc.

DE 10 2009 025 123 describes a radiation emitting device having an organic radiation emitting functional layer and a radiation output layer.

WO 2006/127367 describes a backlit display device in which a diffusion film has polycarbonate and a diffusion pigment which are pressed.

US 2010/328925 A1 describes a particular illumination device.

US 2007/0060704 discloses the use of a polycarbonate composition comprising a diffusion pigment in a diffuser panel.

JP 06-123802 describes a diffusion film having a thickness of 100 to 500 μm for an LCD having a refractive index difference of at least 0.05 on a transparent substrate and transparent light-diffusing particles. One side of the film is smooth, and the diffusion additive protrudes from the surface of the other side to form a structured surface. The diffusion additive has a particle size of 10 to 120 μm.

Despite the use of a cool white LED lamp, one of the objects of the present invention is to provide LED light, comfortable "warm" light perception, and/or, in the case of RGB (red/green/blue) LED use, the most likely Color authenticity or light blue, "fresh" visual impression, whether or not the LED is on or off. The PC board used for this purpose, also known as a diffuser sheet or a diffusing sheet, should have the greatest light transmittance and the best possible light diffusibility at the same time. This polycarbonate diffuser additionally has better flame retardancy and impact resistance than acrylic sheets. Furthermore, the polycarbonate diffusing sheet can be thermoformed (including sharp edges) without completely losing its ability to diffuse.

The light diffusing polycarbonate sheet specified below has been found to meet these requirements.

The above cited documents do not describe the use of the light diffusing PC board described below as a lampshade, more particularly a distance of 15 mm from the light source, preferably 20 mm, especially 30 mm to 100 mm, preferably 80 Mm, preferably for LED applications. These spots are generally visible at a distance of less than 30 mm. If this effect is desired, the corresponding distance of the light diffusing plate from the light source should be maintained. A further better distance is 50 mm to 80 mm. These documents do not disclose that the use of the PC board is described as achieving the above requirements.

The invention therefore provides for the use of a light diffusing polycarbonate sheet comprising a composition comprising (A) 99.9 to 80% by weight of polycarbonate; and (B) 0.1 to 20% by weight of a diffusion pigment It is selected from at least one of the group consisting of a polyoxyxene resin and an acrylic resin; as a lampshade, preferably in the application of an LED lamp.

Component A)

Suitable polycarbonates A) are all known polycarbonates, as described in WO 2007/039130 and WO 2007/039131. These are homopolycarbonates, copolycarbonates and thermoplastic polyester carbonates. Preferably, the polycarbonates are prepared by interfacially from a dihydroxyaryl compound (also referred to herein as a diphenol) and phosgene, or from a melt transesterification of a diphenol and a diaryl carbonate derivative. .

Preferred diphenols are selected from the group consisting of resorcinol, 4,4'-dihydroxydiphenol, bis(4-hydroxyphenyl)diphenylmethane, 1,1-bis(4-hydroxyphenyl)-1. -ethylbenzene, bis(4-hydroxyphenyl)-1-(1-naphthyl)ethane, bis(4-hydroxyphenyl)-1-(2-naphthyl)ethane, 2,2-double (4-hydroxyphenyl)propane, 2,2-bis(3,5-dimethyl-4-hydroxyphenyl)propane, 1,1-bis(4-hydroxyphenyl)cyclohexane, 1,1 - bis(3,5-dimethyl-4-hydroxyphenyl)cyclohexane, 1,1-bis(4- Hydroxyphenyl)-3,3,5-trimethylcyclohexane, 1,1'-bis(4-hydroxyphenyl)-3-diisopropylbenzene, and 1,1'-bis(4-hydroxyl) Phenyl)-4-diisopropylbenzene. Mixtures of such diphenols can also be used in the same manner.

Particularly preferred is 4,4'-dihydroxydiphenyl, 2,2-bis(4-hydroxyphenyl)propane or bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane. Or a mixture thereof.

For the preparation of copolycarbonates, it is also possible to use from 1 to 25% by weight, preferably from 2.5 to 25% by weight (based on the total amount of diphenols used for this purpose) of polydiorganofluorenes having hydroxyaryloxy end groups alkyl.

Also suitable are polyestercarbonates and block copolyestercarbonates, as described in particular in WO 2000/26275. The aromatic dihalide halide used to prepare the aromatic polyester carbonate is preferably isophthalic acid, terephthalic acid, diphenyl ether 4,4'-dicarboxylic acid, and naphthalene-2,6-dicarboxylic acid. Dichlorobenzene.

The polydiorganotoxime-polycarbonate block copolymers are characterized in that they contain a first aromatic carbonate structural unit (1) and a second polyoxynoprene having an aryloxy end group in the polymer chain. Alkane (2) (for example US-A 3 189 662, US-A 3 821 325 and US-A 3 832 419).

Suitable polycarbonates preferably have an average molecular weight 18,000 to 40,000, preferably 20,000 to 36,000, especially 23,000 to 33,000. The weight average molecular weight Mw is determined by colloidal permeation chromatography and calibration with polycarbonate standards.

These polycarbonates generally have an MFR (solution flow rate) value of from 2 to 60 g/10 min, preferably from 2 to 40 g/10 min, more preferably from 3 to 18 g/10 min, especially 5 to 13 g/10 min, based on ISO 1133 is measured at a temperature of 300 ° C and a load of 1.2 kg.

Component B)

The diffusion pigment used can be any acrylate resin having a thermal stability sufficiently high up to 300 ° C so that it does not decompose at the processing temperature of the polycarbonate. Again, the pigment must not have any functionality that would result in degradation of the polymer chain of the polycarbonate. A preferred acrylate resin is a polyalkyl acrylate having preferably from 2 to 8 carbon atoms in the alkyl group and having an average particle diameter (number average) of from 0.5 μm to 80 μm, preferably from 2 μm to 40 μm, especially 3 μm to 15 μm, especially 3 μm to 9 μm. Mixtures of alkyl acrylates can likewise be used (homopolymer or copolymer). The acrylate resins are preferably crosslinkers, and suitable crosslinkers are crosslinkers known for use in acrylates. Preferred crosslinking agents are ethylene glycol based crosslinking agents such as, more particularly, ethylene glycol dimethacrylate.

Particularly preferred is crosslinked polymethyl methacrylate, especially crosslinked with ethylene glycol dimethacrylate.

Commercially suitable polyalkyl acrylates are, for example, products from the Techpolymer® product line of Sekisui, Japan, Techpolymer® MBX-5 or MBX-8.

The polyoxygenated resins preferably have an average particle diameter (number average) of from 0.5 μm to 100 μm, preferably from 0.5 μm to 20 μm, particularly from 1 μm to 6 μm.

In a preferred embodiment, the polyoxyxylene resin is a silsesquioxane, preferably derived from an alkyl semioxane. The group is preferably a C1 to C4-alkyl hemidecane, more preferably a methyl sulfoxane.

Commercially suitable semi-oxanes are, for example, products of the Tospearl® product line from Momentive, USA, Tospearl® TSR9000 or 120S.

The masterbatch typically comprises from 75 to 99.9% by weight, preferably from 82 to 99% by weight, more preferably from 87 to 98% by weight of polycarbonate, and from 25 to 0.1% by weight, preferably from 18 to 1 by weight. More preferably, 10 to 2% by weight of the diffusion pigment B-1), in each case based on the masterbatch composition.

These diffusion pigments are typically used in the masterbatch form, preferably in polycarbonate. Polycarbonates suitable for use in the manufacture of masterbatch are the above-mentioned polycarbonates.

Component B-1-acrylate

The masterbatch typically comprises from 60 to 99.9% by weight, preferably from 70 to 99% by weight, more preferably from 77 to 98% by weight of polycarbonate, and from 40 to 0.1% by weight, preferably from 30 to 1 by weight. More preferably, 20 to 2% by weight of the diffusion pigment B-1), in each case based on the masterbatch composition.

Component B-2-polyoxyl resin

The masterbatch typically comprises from 75 to 99.9% by weight, preferably from 82 to 99% by weight, more preferably from 87 to 98% by weight of polycarbonate, and from 25 to 0.1% by weight, preferably from 18 to 1 by weight. %, more preferably 10 to 2% by weight of the diffusion pigment B-2), in each case based on the mother Material composition.

The master batches are produced by a generally known method, for example, by mixing the components, and then compounding on a kneading extruder (single-screw or twin-screw extruder) or a general extruder.

The thickness of the PC board for LED lamp applications is typically from 0.5 mm to 10 mm, preferably from 0.8 mm to 8 mm, more preferably from 1 mm to 5 mm, and especially from 1 mm to 3.5 mm.

When blue light and thus cold light perception are preferred, a masterbatch based on polyoxyxylene resin is used, and is preferably used with an optical brightener. The preferred amount of polyoxyxene resin for this use form is preferably from 0.1 to 1% by weight, based on components A) and B).

Thus, the PC sheets may additionally comprise from 0.001 to 2% by weight, more preferably from 0.003 to 0.8% by weight, still more preferably from 0.004 to 0.2% by weight, from 0.005 to 0.015% by weight, more preferably in further embodiments. 0.005 to 0.01% by weight (based on the overall composition) of an optical brightener, suitable optical brighteners are derived from bisbenzo A structural type of azole, phenylcoumarin or bisstyrylbiphenyl.

A preferred optical brightener is 2,5-thiophenediyl bis (5-tert-butyl-1,3-benzo) Oxazole), available under the trade name Uvitex OB from BASF SE, Ludwigshafen or Eastobrite OB under the trade name Eastman Chemical Comp.

Further, the composition of the PC board may contain 0.01 to 10% by weight of a UV absorber, and a suitable UV absorber such as a benzotriazole derivative, a dimeric benzotriazole derivative, or the like Derivative, dimerization Derivatives and diaryl cyanoacrylates. They are preferably used in an amount of from 0.01 to 1% by weight based on the total composition.

The benzotriazole-based UV absorber is, for example, and preferably 2-(3',5'-bis(1,1-dimethylphenyl)-2'-hydroxyphenyl)benzotriazole (Tinuvin) ® 234, BASF SE, Ludwigshafen), 2-(2'-hydroxy-5'-(t-octyl)phenyl)benzotriazole (Tinuvin® 329, BASF SE, Ludwigshafen), 2-(2'- Hydroxy-3'-(2-butyl)-5'-(t-butyl)phenyl)benzotriazole (Tinuvin® 350, BASF SE, Ludwigshafen) and bis(3-(2H-benzotriazole) Base)-2-hydroxy-5-t-octyl)methane (Tinuvin® 360, BASF SE, Ludwigshafen).

three A UV absorber of the type is, for example, and preferably 2-(4,6-diphenyl-1,3,5-three 2-yl)-5-(hexyloxy)phenol (Tinuvin® 1577, BASF SE, Ludwigshafen) and 2-[2-hydroxy-4-(2-ethylhexyl)oxy]phenyl-4,6 - bis(4-phenyl)phenyl-1,3,5-three (CGX UVA 006, BASF SE, Ludwigshafen).

Diphenyl ketone UV absorbers such as, and preferably 2,4-dihydroxydiphenyl ketone (Chimasorb® 22, BASF SE, Ludwigshafen) and 2-hydroxy-4-(octyloxy)diphenyl Ketone (Chimasorb® 81, BASF SE, Ludwigshafen).

Further, UV absorbers derived from cyanoacrylates and malonic esters can be used, for example and preferably 1,3-bis[(2'-cyano-3',3'-diphenylpropene fluorene) Alkyloxy]-2,2-bis{[(2'-cyano-3',3'-diphenylpropenyl)oxy]methyl}propane (Uvinul® 3030, BASF SE Ludwigshafen) or 2,2'-(1,4-phenylene dimethylene)dimalonic acid Ethyl ester (Hostavin® B-Cap, Clariant AG).

As additional additives and processing aids, stabilizers, release aids and/or antistatic agents may be added. Suitable stabilizers are, for example, phosphines, phosphites or hydrazine-containing stabilizers and the additional compounds described in EP-A 0 500 496. Examples include triphenyl phosphite, diphenylalkyl phosphite, phenyl dialkyl phosphite, tris(phenyl) phosphite, bismuth (2,4-di-t-butylphenyl) 4,4'-linked diphenyl bisphosphite, bis(2,4-dicumylphenyl)neopentyl diol diphosphite and triaryl phosphite. It is particularly preferred to provide triphenylphosphine and phosphite (2,4-di-t-butylphenyl) ester.

Suitable release agents are, for example, esters or partial esters of mono- to hexahydric alcohols, in particular glycerol, neopentylol or Guerbet alcohol.

The unit alcohols are, for example, stearyl alcohol, cetyl alcohol and Guerbet alcohol; glycols such as ethylene glycol, trihydric alcohols such as glycerol, tetrahydric alcohols such as pentaerythritol and medium erythritol The pentahydric alcohols are, for example, arabitol, ribitol, and xylitol, and the hexahydric alcohols are, for example, mannitol, sorbitol (glucitol), and galactitol.

The esters are preferably monoesters, diesters, triesters, tetraesters, pentaesters and hexaesters or mixtures thereof, in particular saturated aliphatic _C10 to _C36 -monocarboxylic acids and optionally hydroxyl groups. Any mixture of carboxylic acids is preferably a saturated aliphatic _C14 to _C32 -monocarboxylic acid and optionally a hydroxy monocarboxylic acid.

Commercially available fatty acid esters, particularly fatty acid esters of pentaerythritol and glycerol, may contain <60% of different partial esters as a result of the preparation.

A saturated aliphatic monocarboxylic acid having 10 to 36 carbon atoms such as citric acid, lauric acid, myristic acid, palmitic acid, stearic acid, hydroxystearic acid, arachic acid, rosin, twenty-four Acid, wax acid and octadecanoic acid.

Suitable antistatic agents are cationically active compounds, such as quaternary ammonium, phosphonium or phosphonium salts; anionic active compounds such as alkylsulfonates, alkyl sulfates, alkyl phosphates, in the form of alkali metal or alkaline earth metal salts, Carboxylates; nonionic compounds such as polyethylene glycol esters, polyethylene glycol ethers, fatty acid esters, ethoxylated aliphatic amines. Preferred antistatic agents are nonionic compounds.

The composition still contains a pigment such as a yellow pigment or titanium dioxide. In this way, the hue can be deeper.

A UV protective layer such as a PC plate containing a UV absorber or a coating layer containing a UV absorber may be provided on one side or both sides of the PC board. Suitable UV absorbers are those mentioned above.

The components A and B and further optional additives are mixed and compounded in a conventional manner and processed into granules. A known extrusion process produces a PC board from pellets.

With regard to extrusion, polycarbonate pellets are supplied to the extruder and melted into the plasticizing system of the extruder. The polymer melt is forced through the groove film and molded, and is transformed into a desired final shape in the nip of the smooth calender, and the shape is fixed by reciprocating cooling on the chill roll under ambient air. . The polycarbonate having high melt viscosity for extrusion is usually processed at a melting temperature of 260 to 320 ° C, preferably 270 to 300 ° C, and the cylinder temperature of the plasticizing cylinder and the mold temperature are set as such.

The polycarbonate melt of the various compositions can be superposed by the use of a co-extruder. By means of a co-extruder, for example, a UV protective layer can be provided.

These PC diffusers are used as cover panels or shades for so-called lighting units. Preferred lighting units use LEDs as the light source.

The invention therefore also provides a lighting unit, preferably an LED lighting unit, comprising the PC board described above. Preferably, the diffuser plate has a self-light source, preferably from the LED, at a distance of 50 to 80 mm. At this distance, optimum diffusion and thus excellent light perception are achieved.

By using a polycarbonate sheet as the lampshade, the illumination temperature is reduced by at least 150 to a maximum of 500 K, preferably 200 to 400 K, in the case of warm white light compared to the illumination temperature of the LED. In the case of cool white/blue light, the reduction is at least 80 K and the maximum is 150 K. The difference in illumination temperature, ie the reduction, is measured here on a polycarbonate plate having a thickness of 3 mm. The illumination temperature is determined by the method of a spectrometer (DIN 5033). Lights or lighting units comprising these diffusing panels, in particular LED lights or LED lighting units, for example as office lighting, street lighting, floor lighting, etc., in advertising panels or as advertising panels, may also be suitable for decorative purposes, and As front lighting as well as in the refrigerator.

The following examples are intended to illustrate, but not limit, the invention.

A1) Makrolon® 2600 from Bayer Material Science AG, based on a polycarbonate having a bisphenol A (measured according to DIN EN ISO 1133, measured at 1.2 kg and 300 ° C) with an MVR measurement of 11.5 g/10 min.

A2) Makrolon® 2805MAS152 is from Bayer Material Science AG based on a polycarbonate having a bisphenol A (measured according to DIN EN ISO 1133, measured at 1.2 kg and 300 ° C) with a MVR measurement of 10 g/10 min.

Component B)

B1)Techpolymer MBX-5 from Sekisui, Japan, an acrylate resin (methyl methacrylate/ethylene glycol dimethacrylate copolymer) having a particle size of 2 to 15 μm and an average particle diameter of 5 μm. .

B2) Tospearl TRS9000 from Momentive Performance Materials, Germany, has a polyoxyxylene resin having an average particle size of 2 μm.

Masterbatch (MB) 1 is obtained from:

̇77.9 wt% Makrolon® 2600

̇ 20% by weight according to B1) of Techpolymer according to B1)

̇ 0.10% by weight of triphenylphosphine and 2% of phosphate as a further heat stabilizer.

Masterbatch (MB) 2 is obtained from:

̇88.35 wt% Makrolon® 2805MAS152

̇10% by weight according to B2) Tospearl 9000 and

̇1.10% by weight of Eastobrite OB

̇0.55 wt% antioxidant

Example 1:

A compound having the following composition is obtained from:

̇93.5 wt% polycarbonate A1)

̇6.5 wt% of masterbatch B1) (corresponding to 1.3 wt% in the composition according to B1's Techpolymer)

Example 2:

A compound having the following composition is obtained from:

̇97% by weight of polycarbonate A2

̇3% by weight of the masterbatch B2 (corresponding to 0.3% by weight of the composition according to B2's Tospearl)

The compositions according to Examples 1 and 2 were used to make panels by mixing the components and extruding them into sheets.

The panel 1 made from the composition according to Example 1 had a thickness of 3 mm.

The light transmittance τ _(A) or τ _(D65) is measured by the CIE standard illuminators A and D65 and the light diffusion factor σ.

The light transmittance was measured by a CIE 130-1998 in a visible light wavelength range with a spherical photometer having a diameter of 1.5 m.

The light transmittance τ _(A) of the board 1 was 0.72; the comparison value τ _(D65) was 0.72.

The light diffusing factor was measured by DIN 5036 as a pivot arm device using an L-grade photometer (obtained from LMT) and a Class A photometer (obtained from Czibula & Grundmann GmbH).

The light diffusion factor σ is 0.65 for the plate 1 at a half value angle γ60°.

In addition, the illumination temperature was measured (by means of a spectrometer), the illumination temperature of the LED was 5940 K, and the illumination temperature of the LED masked by the panel 1 (thickness 3 mm) was 5718 K with a difference of 222 K.

Thus the LED masked by the panel 1 has a more comfortable light illumination than the LED.

Claims (14)

A use of a light diffusing polycarbonate sheet comprising a composition comprising: A) from 99.9 to 80% by weight of polycarbonate; and B) from 0.1 to 20% by weight of a diffusion pigment selected from the group consisting of enamel resins and At least one of the group consisting of acrylic resins; used as a lampshade. The use of the light-diffusing polycarbonate sheet of claim 1 is for use as a lampshade in LED lighting applications. The use of the light-diffusing polycarbonate sheet of claim 1 wherein the polycarbonate sheet is at a distance of from 15 mm to 80 mm from the light source. The use of the light-diffusing polycarbonate sheet of claim 1, wherein the composition comprises 0.1 to 20% by weight of a polyoxynoxy resin and 0.005 to 0.01% of an optical brightener, and the balance to 100% by weight Polycarbonate. The use according to claims 1 and 4, wherein the polyoxyxylene resin is based on an amount of from 0.1 to 1% by weight of the component A) and the component B). The use according to item 4 of the claim, wherein the polyoxyxylene resin is based on the components A) and B) and the optical brightener in an amount of from 0.1 to 1% by weight. According to the use of item 3 of the claim, wherein the plate is at a distance of 30 mm to 80 mm. According to the use of item 5 of the claim, wherein the optical brightener is It is now an amount of 0.005 to 0.015 wt%. The use according to Item 1 of the claim, wherein the polycarbonate sheet has a thickness of from 0.5 mm to 12 mm. The use according to Item 1 of the claim, wherein the polycarbonate sheet has a thickness of from 1 mm to 6 mm. The use according to Item 1 of the claim, wherein the polycarbonate sheet has a thickness of from 1 mm to 3.5 mm. A lighting unit comprising a polycarbonate sheet according to item 1 of the claim. A lighting unit according to item 10 of the claim, which comprises a polycarbonate plate and LEDs. According to the use of item 1 of the request, it is used for the manufacture of warm white or cool white-blue lamps, which are fixed at a distance of 50 mm to 80 mm from the light source.