US2599739A - Cathode-ray tube - Google Patents

Description

June 10, 1952 R." B. BARNES 2,599,739

CATHODE-RAY TUBE Filed April 12, 1950 2 SHEETS-Sl-IEET 1 INVENTOR ROBERT Bowuue BARNES AT'I'O NEY K W a? 4 E \A //////=a v June 10, 1952 B. BARNES 2,599,739

CATHODE-RAY TUBE Filed April 12, 1950 2 SHEETS-SHEET 2 INVENTOK ROBERT BOWUNG BARNES ATTOKN Y Patented June 10, 1952 CATHODE-RAY TUBE Robert Bowling Barnes, Stamford, Conn., assig-nor to American Optical Company, Southbridge, Mass., a voluntary association of Massachusetts Application April 12, 1950, Serial No. 155,514

13 Claims. 1

This invention relates to cathode ray tubes and has particular reference to novel means of improving the definition and contrast of images produced on the screens of such tubes.

In conventional types of cathode ray tubes such as used in television receiving apparatus or similardevices images are produced on a fluorescent screen when the particles forming said screen are bombarded by an electron beam and are caused to fluoresce in proportion to the intensity of the electrons of said beams. In such a device when a fluorescentparticle has been made tofluoresce by the electrons, some of the light emitted from said particle isreflected back onto the screen from the surfaces of the tube face. This will cause illumination of other particles of the screen by the light so reflected and produce undesirable halations. Such halations tend to reduce contrast and definition of the image formed on the screen.

Therefore, it is a principal object of this invention to provide a cathode ray tube with means for reducing halation by eliminating to a substantial degree the amount of light reflected from the surfaces of the tube face onto the fluorescent screen.

Another object is. to provide means for reducing halati'on in a cathode ray tube by providing the outer surface of the tube face with a reflection reduction coating for substantially decreasing the amount of light which may be reflected onto'the fluorescent screen from said outer surface and to simultaneously reduce reflections fromv said surface caused by light rays from sources outside the tube.

Another object is to provide the inner surface of the tube face with a reflection reduction coating between the material of the tube face and the fluorescent screen, which coating, due to its natural characteristics, will considerably reduce the amount of reflected light reaching the fluorescent screen.

Another object is to provide a cathode ray tube with means on the periphery of the face portion thereof -for preventing light rays striking said periphery from being reflected back toward the fluorescent screen, said means being in the form of 'a highly polished surface for permitting said light rays to escape, or a light absorbing coating on said periphery for absorbing the light ra s.

Zinother object is to provide a cathode ray tube with means whereby fluorescent material on the tube face outside of the desired image area will be prevented from fluorescing and causing possible additional halation within the image area.

Other objects and advantages of the invention will become apparent from the following description taken in connection with the accompanying drawings in which:

Fig. 1 is a side elevational view partly in sectionof a cathode ray tube embodying the inven 7 tion;

Fig. 2 is an enlarged fragmentary sectional view of a portion of the tube face taken on line 22 ofFig.1;

Fig. 3 is a fragmentary side elevational view of the forward end portion of a cathode ray tube; v Fig. 4 is a diagrammatic illustration of light rays emitted by a fluorescent particle in accordance with conventional prior art devices of this nature; Fig. 5 is a diagrammatic illustration of effect of the present invention upon the light rays emitted by a fluorescent particle;

Fig. 6 is a fragmentary sectional view of a conventional tube face adjacent the periphery there: I

of; and

Fig. 7 is a fragmentary sectional view similar to Fig. 6 illustrating a further feature of the invention.

Referring to the drawings wherein like characters of reference designate like parts throughout the several views, Fig. 1 illustrates a cathode ray' tube embodying a neck portion [0, substantially I conical sides I I, and a face portion [2 all of which may be formed integrally of a suitable glass. However, the sides II and neck Ill may be formed of metal and the face portion I! alone formed of glass, if desired, whereupon the glass must be The inner surface suitably sealed to the metal. of the tube face portion I2 is provided with a fluorescent screen I3 composed of a myriad of I fluorescent screen, designated by numeral I 4 in Fig. 4, is caused to fluoresce, thelight emitted thereby will pass into and through the glass of the face portion l2 substantially as illustrateddiagrammatically in Fig. 4. Light rays I5 passing through the glass along paths normal to the surfaces of the glass will emerge from the outer surface l6 thereof with no deviations. However,

light rays l1 directed through the glass at an angle less than the minimum angle of total re-- partially reflected, as illustrated at 2| emanating from the fluorescent particle M and directed toward the outer surface l6. of the glass at an angle greater than the critical angle will be totally reflected by the outersu-r'faceilfi and will pass rearwardly through the glas's" asindicated by numeral 22 to 'therear surface 2i! where they will cause illumination of still other particles Mb of the fluorescentscreen whieh a rein optical contact with said glass. Such light rays which strike the front surface It of the glass at angles greater than the critical angle will be refl' ed; back and" forth from the respective of any suitable type which is adapted to reduce 1,

the "am u t org-nightreflected from the surface. S'uch acoating rnay'be any one 'ofthe many well-known types such asisproduced by evaporaf" tion ofj'calciuni orother fluorides)- on a glass surface,- br rbrmea by wetting theg'la'ss with 'silicicacidandtreating with hydrochloric acid copra cipitatefthe silicon dioxide, another-type is made as a film of b'arium Stearate "which is produced by dipping the glass in Water containing barium d ving a layer of 'stearic acid; on 1 top; at of magnesium I fluoridegcalcium ee so ium ffiu'orid or? 'sodiurn aluminum still others are chemical decomposi- 1t a The preferred;- reflection reduction; coating,

hqweyer; is forifnedj of a composition consisting ollbidal'- 'su'spensioncontaining: fromgatout 0. to G-IO per centby weight of sub' microscopic'; micfofgranular; discrete particles 3 of solid anhydifoustransparent material such as magnesium fiucridel- 'lithium fluoride, strontium fluoride, calciumfluoride, barium fluoride or cr'yolitesubstairtially uniformly dispersed injafvolltile liduid mes o thef particles, with the-particles being approximately spherical in shape and l'ess- 'than 625 angstroms in diameter. A-glass surface can 4 the concentration of the particles in the irregularities decreasing from the surface of the tube face outward, and the material of the particles being such that the effective index of refraction of the coatings varies from substantially unity at the layer-air interface to an indexyaluei which progressively-increases as it approaches the material of the tube face portion l2 until it substantially approximates the index of refraction of the. glass of the tube face portion. Such a coating will increase the transmission of light rays-J26 fromthesurface [6 with a consequent 'de creasein the" reflected light rays 24 (Fig. ascompare'd with; the normal reflection 19 (Fig. 4). By comparing-Figs. 4 and 5, it will be understood that by providing the surface 16 with the coating ze a negligible amount of light will be reflected toward the fluorescent screen 13 from light rays striking the surface H5 at angles less than; the: critical angle; Gonsequentlyrparticles Met will manly-slightly if at-all illuminated b suchlreflections.

In addition, it is. pointedv out; hereihahthe coating 25 will also preventreflection ntc an observerfs; eyesof light. rays; strikinel the: tube: face. portion from sources outsidethe tube; This; feature is: particularly desirable r since; it conside erably improves; the. visibility of: the; image 7 To further eliminate, halationsthe innerrsuri faceizo-ofi thetube; face portion Ilmay bBJDZ'Qz: vided with a similanreflection reductiomcoatine; 21;. the-l coating 25.5 being; disposed: between. the; surface: 20 and; they fluorescent screens. 13;

Fi'g. '2:.is a. greatly; enlarged fragmentary; diesgrammatical sectional ;view; througlila: portionzof" thetube. face [2: and. diagrammatically shows a the coatings 21; arid52-5 provided-on the innertan'd outer-surfaces 2'0 and I6 respectively.

surfaces of the tube face. as-a plurality; ofminute irregularities 28 each of which is. formed; of: a

plurality of minute particlesxi The fluorescent:

zinc silicate, zinc b'erylliumlsili-cate, zinc cadmium sulphide; zinc beryllium tzir'conium silicateg zincborate, I cadmium v tungstate'; and-:1 etherv knownr.

materials of mixtures thereof; v

'Itwillbe noted that the particles: M' comprisingthe fluorescent screen are substantially '7 largezithanftl ie' particles 29 "of the reflection 'reduction coatings, 'be-ing-from 1 to6' microns in diameter if applied by spraying. Howevemaa largenpanticles} froni 10 to 3Q microns in diameter are 1 13} deposited on; the screen by dustingor: settl ng through air. Thus, when a fluorescentcoatlng I 3f is applied over the inner reflection reduction" coating 2-1; the particles 14 will; due to be "prpvided with the oeatingby awningw me:-

surface at n layer ofthe abev'e composition 'and subj ectin'g 1 to heatto evaporate the liquid'and mate survcoating of the particles on-'the=surface, 'it beingdesirabletocontrol the 'amount'ofthe -composition-- applied and the concentration offthe' 'particlesin the suspension so as to produce a ceaunghavmg aresultantthickness of 'approximately one quarter wave-length of light;

The forming 1 of i such a coating on I the glass surface will 'omprise{sub-microscopic, discrete;

micro 'g'ranula'r transparent solid particles which ar' 'dposited onthe'gla'sssurface so as reformminute -projecting irregularities on said surfac;'

their 1 large size, engage the irregularities 28: in. such fashion that a plurality of vacant spa'cesi 30 'Wi11'Ibe provided between :the' coating-'21 and screen-l3.

Upon- .again on paringFigs- 44:andfiy-liswillfbeis seen thatl halation i'sr'ediiced byapplyifigithereek nection reduction coating 27' "to the' -inner-surface 2 0 pf thetube 'fa'ce portion I 2 3 as described si'n'cesthe light rays 21 whichstrike-thesurface-l 6;at

angles greater than the critical angleand are totally reflected back through the glass to the: surface Z Othereof willbe' prevented bythe-reflection reduction coating 21 from directly-strik ingf and consequently illuminating particles; I 417 of"theifinorescent s-creeni Itl will beunderstood that if the particles ta-are marred ngagemem i 11; will: be noted that the coatings are disposed 0111131516.;

with the surface 20, as in the conventional cathode ray tube, they would be illuminated by the light rays 22, but by spacing the particles from the surface 20, the reflected light rays will be prevented from directly illuminating the particles. The inner reflection reduction coating 21 also greatly minimizes reflection back into the fluorescent material of light from the inner surface of the glass i2.

Another cause of halation, particularly in the edge areas of the image, is shown in Fig. 6, Wherein the fluorescent screen I3 is disposed directly upon the inner surface 20 of the tube face [2 by conventional methods which causes a supply of the fluorescent material (3 to be deposited on the inner surface of the side walls ll of the tube adjacent their junction with the face portion i2. l'hus, when fluorescent particles in this area are made to fluoresce when bombarded by an electron beam 32, light rays therefrom will pass in all directions and will, as indicated by lines 3|, illuminate other portions of the fluorescent screen 13, subsequently causing a reduction in contrast discrimination in the image. To overcome this, several methods maybe used. For example the fluorescent material in this marginal area may be removed or covered with a coating of material which would prevent the particles so covered from being effected by the electron beam, or means may be provided internally of the tube for limiting the image area by preventing the electron stream 32 from striking the fluorescent material in these areas. Therefore, means such as a ring-like member 33 may be inserted in the tube during the fabrication thereof with the size of the central opening of said member 33 being controlled so that the electron beam 32 will be prevented from striking the fluorescent screen 13 in the marginal areas thereof and thus will limit the size of the desired effective image area. Fig. '7 illustrates this feature and shows the electron beam 32 striking the fluorescent screen l3 at the margin of the desired image area, with the ring-like member 33 functioning as a baffle or stop for preventing the electron stream 32 from striking the fluorescent material in the marginal area 34 of the screen i3, and thus preventing undesirable halations from this source.

To reduce further the amount of undesirable light within the material of the tube face portion i2 which may be reflected upon the fluorescent screen l3 .and cause undesirable halations, some of the light rays within the glass, particularly in the marginal areas of the face portion 12, can be'made to emerge from the glass by providing the outer edge of the face portion l2 with a highly'polished peripheral surface 23 (Fig. 3). This will permit without diffusion the escape of stray light rays which strike this surface at'angles less than the critical angle as shown by dotted lines 22a in Fig. 5. It should be understood that this portion may be coated on either or both surfaces with reflection reduction coatings to reduce reflection below the critical angle.

If desired, the peripheral surface 23 may be coated with a light-absorbing material such as a suspension of graphite particles in oil or cement such as Canada balsam, or black lacqueiywhich coating should possess an index of refraction equal to or higher than the index of refraction of the tube face portion I2 for maximum eiflciency.

Thus, light rays 22 (Fig. 5) striking the various surfaces at angles less than the critical angle may be either'permitted to escape through the highly polishedsuri'ace 23 as shown by dotted lines 22a, or may beabsorbed by the absorbent coating 35.

From the foregoing, it will be seen that means and methods of a novel nature have been employed for accomplishing all of the objects and advantages of the invention.

While the novel features of the invention have been shown and described and are pointed out in the annexed claims, it will be understood that many changes may bemade in the details shown and described without departing from the spirit of the invention. I, therefore, do notwish to be limited to the exact details shown and described as the preferred only are set forth by way of illustration.

I claim:

l. A cathode ray tube embodying a transparen face portion having a coating of transparent material on the rear surface thereof with a coating of fluorescent material on said transparent material having its effective portion confined to substantially the area desired of the resultant image and spaced from the inner surface of said transparent face portion by said transparent material, said face portion having a transparent light transmission increasing reflection reduction coating on the front surface thereof and having light controlling means surrounding the periphery thereof, said tube having means for producreflection reduction coating on the outer surface of the transparent face portion having an optical thickness and effective index of refraction such that it, While functioning to reduce reflection of the fluorescent material by light rays at angles greater than the critical angle reflected from the inner side of the front surface of the face portion and said light rays at angles greater than the critical angle when at the periphery of the face portion being effectively obviated by said periph eral light controlling means.

2. A cathode ray tube embodying a transparent 3 face portion having a fluorescent screen'adjacent its inner surface, means for producing a the critical angle, and means forreducing undesirable illumination of said fluorescent screen comprising a reflection reduction coating dis posed upon the outer surface of said transparentface portion for reducing reflection of light'from sources outside the tube, said reflection reduction coating being formed of transparent material having an optical thickness and an effective index of refraction as to simultaneously increase transmission of light rays from said luminous spot by reducing reflections of said light rays emitted by said luminous spot and striking said outer guyase at angles: lss thani the criticalanei i transparent coatmgionzthednnera surface of saidtransparent face portion for supporting: said fluorescent screen in spaced; relation. with said transparent face portion and reducingmefiections of: lightrays. emitted by 'saidi'luminous spot-amt striking said outer surfaceatiang-Ies greaten than theicriticat angle; and meansi'om the peripheral edge of:saidtransparenttftmcaportion for reducew inge. reflection of light rays: emitted by? said. luminous; spotiand' striking-1 said; peripheraledge;

A'cathoderay 'tube embodyingwtranspa-rent" face portion. havingea: fluorescent: screen? adja-.. cent:itszinnerisurfacezcomposedeof aiplurality' -of contiguously related-particles-of fiuorescent ma terial, means for producing a beam of electrons and directing it upon said particles: off: the fluorescent screen: to: produce a luminous spot thereon;- said l'uminousspot emitting" light: rays. StflkiDgE-i the: surfaces OfSQfldif. transparent face, pcntionalt angles both less than and greater than the critical; angle, andmea-ns rfor'reducingi v desirable; illumination: of; said fluorescent screen;

comprising. alreflection; reduction coating dis-a p sed. mean heoout rs rface-of saidra spare t ace; uer ionfor reduc nar flection of; li ht from; our es; u s d h -tube; n fo reducin re flections of light-rays; en i-tted -bysaid luminous spot. and t k ia sa o te ;v su ce; at n les -t an he ri i e r n lez air nsparentcoa r: 1112:4011 theinner surfaceof -said transparent facepqr z nr r ducin v-r flee on l t. aysmitte v oyaidiumin u p t n v tr li i J aid ute ii aqeat n les; re er han; h ri ca e aidt nspar nt c a in omp sin a. layer; of subemigroscopic, discrete, micro-granu- 1; l-irans en 1101 ar i e a; i e en i e -r b r ma enmm he flmr s nt. par ic esem t saidicoating} and: approacnes tlfeeindexior'refrac tien ofithe material of said face-portion, a seeomr reflection reduction coatingon the-innen surfacel: of- 'said transparent face portion; said seconct re fiection reduction" coating being- -si milar to saifl first reflection-'-reductioncoating with the;irregu laritiesthereof causing; said fluorescentsereeni to be retained in spaced relation witl i satransparent face portion to reduce tneilIHminaJ- tim of the fluorescent. screen by the-light rays emittedx by said-luminous spot 'anet-refiected,15y said' outersurface; and 'means orrthe-periplieraF edge of said transparent feca -portion for 'r'educ ing; reflections of light rays" emitted by== said lumimq l g' ndi striking said peripheraledge-w 5;.- A'- cath'cde ray tube'embodying a transparent face portion havinga fluorescent screen adjace its inner-surfaceaymeansfor producingv atbeam electrons and directing it upon saidTflilorescen screen to produce a; luminous spotthereong. sai

1uminous-- spot-- emitting. lig ht' rays striking the? surfaces of said transparent face portionat; angl'esbotliless than-and greater thanftheecritical" angle, means for rediniing undesirable illumination iofsaidfluorescent screen comprise-- ing; a reflection reduction coating disposed upon the; outer surface of ;sa id transparent face-par tion'f'or reducing reflectionoflightr' f rom sources outside thetube and for increasing-transmission of light rays emitted Icy-said"luminousspot and j striking said outer-surface at, angles-lessthanthew criticalangle; a; transparent coating on theinnen surface; of; said transparent faoerportiqn for re taining saidjfiuorescent screen-*iirspacedrelation witli saidtransparent face ortion and; reducing;-

theillurnination of the fluorescent 'screen bglig ht rays emitted by -said lurr'iinousgsp otand reflected r mi ute- -rreaular t eaonaiclinner S lf w wh ch; cau aid part les-of; efluore cent' is 7 screen, to be retained inspacedrelation with said .nar nt ace er -i ns nd'mean i; n he; pen b81 11; d e oi said-transparen a e por on: for; udnareflmfiond e r y mitte hr luminousi petiaedk sin net. said periph r l 4% e hrxlflw ay: u e.- emhodit nee; t a p nt acezpo t on,.h yine.z efiuq escen an ad a en a nne ur wame ns iq tnred eab m ect qnsaand d req ingszt upon; said. reen 1 0919 14655 uminous p e o r e v. l minous; notxemit insrsliaht a s 1strik ne;;the; surfaces f; aid; tran par nt fac rmttinn-v at. analeszboth e srthanuandlereatertha he r ccal angle, and means-for;reduclnggundesiranleumination, of said; uore eentwspr en; mmpr se inaaaflrst light trans siominqreasinsz fle t en reduction-coating; Off transparent;- matcrial dis posed: upon-:the quten surf a'ce'of said-transparent face portion-"forreducing reflection, of: lightfrom; sourceszontside thatubeiandiforzincreasing trans:- m-issiom of: light: raysicemittedz; by. 7 said; luminous:v V spotzandt. striking saidi outer; -surface; at; anglesi lessithanalth'e:crlticailrranglessaid diglit transmi sionainereasingreffection reductionacoatingi comeprisingtgazthm layer- 0f:subemicroscopia; discrete;

fluoresce t;

microf-granulantransparentisolid:particlesqforma l inga minute irregularities on said-i outer surface,

the concentration of ithe said particles: in: the irregularities decreasing from said outer surf ac'eoutwardlyand the material of saidqparticleszbeinga such-that the efiecti-i e-"inden Of refractiOn' ofsaid coating varies--'-from-'sub stantiall unity at the layer-air: interface to -index'-=value which progressively increases in a di-iection inwardly or 75 by .said' outer surface, and means" for=eliminating; some of; the light rays' normally, trapped within.

the material of; said face portion to, prevent re-; fiection thereof ontosaid fluorescent-screen com-- rising a highly; polished; outer-surface formed? on .tne peripner *1; :edg of" said, fa'ce portion; forf. permitting; liglot; rays,- striking; said surface: to' erge-1 7 6f; A catiiodegray tube embodylngja' transparent; face portionhaving; a fluoresoentscreen adjacent?- its inuer ur ace; means q ip ll neia"beainr of electri nsaml dire tinaiit u on: said; fluorescent. reen; o. PJZOQLIQ J 9; vlumin nsisp t there nt fiat dzi miIJQ SL PQt' emittin light rays striking thei ur aces. f; aid transnarent: face; portion at;

n le 'b tliilessg thana rdi reater than ithercriu t means; for d cingirundsirabif. i uminat on; of! said; fluorescent; scr en: comprise ing atransparent coating disposedjupon theouter; surface of 'saidtrarisparent facanorfion anilineing; an optical thickne sv andeanl eff ctive. index. ofretractiontsuchasjo reducerefiection, offliglitj; from sources outside the. tube; andlincreasingthel. transmission of; light 7, rays. emitted. by, said;

minous; spot:andstriking saide outeri surface at;

angles less than the criticaLangle aitransparent;

- t g onsthermnervsnrfaceeofisaifiitran a t' fag-e P- e-- unaqrtina-a aid fluorescent. screen: in spac d re ation-ewitnssaide transparent face n rti niand r ducin thetillumination tuna fluorescentescreen by; ligl t iraysfiemit ed'rb i saidfl umina isn tand'refl ctedibx saidiooutensurfaeetj nd meansrf reeliminating some ofzthalightnrays normally trapped within the material of saidsfa'eee por n: to prer ntrirefiedfiion:thereof: onto; said. i

v 'ZQ igDt L absorbingzs: maftmaizz disposed; onrthesneriplieran 1.:

fluorescermsereen." omprisin ecoatinea edge of said face portion for absorption of light rays striking said surface from within.

7. A cathode ray tube embodying a transparent face portion having a fluorescent screen disposed adjacent the inner side thereof, means for directing electrons -upon said fluorescent screen for producing a luminous spot thereon and a trans-' face portion having a fluorescent screen disposed adjacent the inner side thereof, means for directing electrons upon said fluorescent screen for producing a luminous spot thereon, and a light transmission increasing reflection reduction coating on the outer surface of said face portion which has an optical thickness and effective index of refraction such as to reduce reflections of light from sources outside the tube and to simul taneously increase transmission of light rays emitted by said luminous spot and striking the outer surface of said transparent face portion at angles less than the critical angle, said light transmission increasing reflection reduction coating comprising a thin layer of sub-microscopic, discrete, micro-granular, transparent, solid particles forming minute irregularities on said outer surface, the concentration of the said particles in the irregularities decreasing from said outer surface outwardly and the material of said particles being such that the effective index of refraction of said coating varies from substantially unity at the layer-air interface to an index value which progressively increases in a direction inwardly of said coating and approaches the index of refraction of the material of said face portion.

9. In a cathode ray tube embodying a transparent face portion having a fluorescent screen disposed adjacent the inner side thereof and means for directing electrons upon said fluorescent screen for producing a luminous spot thereon, means for reducing halation produced by light rays emitted by said luminous spot and striking the outer surface of said transparent face portion at angles greater than the critical angle and which are reflected back upon said fluorescent screen comprising a transparent surface reflection reducing coating disposed on said inner surface of the transparent face portion between said inner surface and the fluorescent screen, said reflection reduction coating comprising a thin layer of sub-microscopic, discrete, micro-granular, transparent solid particles piled in theform of minute irregularities on said outer surface, the concentration of the said particles in the irregularities decreasing from said inner surface in a direction toward the fluorescent screen and the material of said particles being such that the effective index of refraction of said coating varies from substantially unity adjacent the fluorescent screen to an index value which progressively increases in a direction inwardly of said coating and approaches the index of refraction of the material of said face portion, the high points of said irregularities. engaging said fluorescent screen and maintaining it in spaced relation with said inner surface to reduce illu- 7 i0 mination of the screen by said reflected light rays.

10. In a cathode ray tube embodying a transparent face portion having a fluorescent screen disposed adjacent the inner side thereofand means for directing electrons upon said fluorescent screen for producing a luminous spot thereon, said luminous spot having'light rays emanating therefrom at angles both less than and greater than thecritical angle, and means for eliminating the major portion of said light rays which are at angles greater than the critical angle comprising a highly polished surface on the peripheral edge of said transparent face'portion for permitting said light rays striking said highly polished surface to pass therethrough.

11. A cathode ray tube embodying a transparent face portion having a fluorescent screenadjacent its inner surface, means for producing a beam of electrons and directing it upon said "fluorescent screen to produce a luminous spot thereon, said luminous spot emitting light rays striking the surfaces of said transparent face portion at angles both less than and greater than 1 the critical angle, and means for reducing'undesirable illumination of said fluorescent screen comprising a reflection reduction coating disposed upon the outer surface of said transparent face portion, said coating being formed of a transparent medium having an effective optical thickness and index of refraction such as to reduce reflection of light from sources outside the tube and to reduce reflections of light rays emitted by said luminous spot and striking said outer surface at angles less than the critical angle while simultaneously increasing the transmission of light rays from said luminous spot through said outer surface, and a transparent coating on the inner surface of said transparent face portion for maintaining said fluorescent screen in spaced relation with said transparent face portion for reducing the illumination of said fluorescent screen by reflections of light rays emitted by said luminous spot.

12. A cathode ray tube embodying a transparent face portion having a fluorescent screen adjacent its inner surface composed of contiguously related particles of fluorescent material, means for producing a beam of electrons and directing it upon said particles of the fluorescent screen to produce a luminous spot thereon, said luminous spot emitting light rays striking the surfaces of said transparent face portion at angles both less than and greater than the critical angle, and means for reducing undesirable illumination of said fluorescent screen comprising a reflection reduction coating of transparent material disposed upon the outer surface of said transparent face portion and having an effective optical thickness and index of refraction such as to reduce reflection of light from sources outside the tube and to increase transmission of light rays emitted by said luminous spot and strikin said outer surface at angles less than the critical angle, and a transparent coating on the inner surface of said transparent face portion for reducing the illumination of said fluorescent screen by reflections of light rays emitted by said luminous spot, said transparent coating comprising arlayer of sub-microscopic, discrete, microgranular, transparent solid particles of a size substantially smaller than said fluorescent particles and formin minute irregularities on said inner surface which cause said fluorescent screen

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