 4a of the prism sheet 4 at an angle close to perpendicularity (.phi.3=approximately 60.degree.). The percentage of such beams incident upon another slope 4b is relatively low.
Next, the representative beam B1 substantially straightly travels in the prism sheet 4 up to the opposite slope 4b to be subjected to regular reflection. The beam which has been subjected to regular reflection impinges upon the flat surface 4e of the prism sheet 4 at an angle close to perpendicularity and exits from the prism sheet 4. This process modifies the preferred propagating direction of the beam emitted from the exiting surface 5 into a direction which is substantially perpendicular to the exiting surface 5.
However, the preferred propagating direction after the modification may be shifted from the direction perpendicular to the exiting surface 5. The shifting angle from the perpendicular direction can be adjusted to some degree depending on the apex angle.phi.3 of the prism sheet 4, the material (refractive index) of the prism sheet 4, and the material (refractive index) of the light scattering guide plate 1.
FIG. 3 shows another configuration of the prism sheet 4 and the behavior of light. In this configuration, the prism surface faces outwardly. For example, the apex angle.phi.4 of each prism element on the prism surface is approximately 70.degree..
In this configuration, the range of the apex angle that provides preferable results is wider than that in the above-described configuration wherein the prism surface faces inwardly.
If it is assumed that the direction of incidence is the direction indicated by the arrow L', a representative beam B2 corresponding to the preferred propagating direction is incident upon the exiting surface 5 at an angle.phi.1=approximately 35.degree.. The beam is mostly emitted into the layer of air AR (having a refractive index n0=1.0). The emitting angle.phi.2 in this case is approximately 60.degree..
The representative beam B2 straightly travels through the layer of air AR and thereafter impinges upon the flat surface 4e of the prism sheet 4 at an angle. It follows a refraction path as illustrated and is emitted from one surface 4c of the prism sheet 4 at an angle close to perpendicularity to the exiting surface 5. The percentage of such beams that are emitted from another surface 4d is relatively low.
The path of the beam after the incidence upon the flat surface 4e of the prism sheet 4 varies depending on the refractive index n2 of the prism sheet 4
4a of the prism sheet 4 at an angle close to perpendicularity (.phi.3 = approximately 60.degree .). The share of such beam incident upon another slope 4b is relatively low. 
 Next, the representative radio beam B1 well straightly travels in the prism sheet 4 up to the opposite gradient 4b to be submit to regular contemplation. The beam which has been subjected to even reflection impinges upon the flat open 4e of the prism sheet 4 at an angle close to perpendicularity and exits from the prism plane 4. This process modifies the preferred spread direction of the beam emitted from the exiting surface 5 into a guidance which is substantially perpendicular to the exiting surface 5. 
 However, the preferred propagating management after the modification may be shifted from the direction perpendicular to the exiting surface 5. The shift angle from the perpendicular direction can be adjusted to some degree depending on the apex angle.phi.3 of the prism sheet 4, the material (refractive exponent) of the prism plane 4, and the material (deflective exponent) of the light scattering guide plate 1. 
 FIG. 3 indicate another configuration of the prism sheet 4 and the behavior of light. In this shape, the prism surface faces outwardly. For example, the apex angle.phi.4 of each prism element on the prism surface is approximately 70.degree.. 
 In this configuration, the range of the apex angle that provides preferable results is wide than that in the above - described shape wherein the prism open faces inwardly. 
 If it is assumed that the direction of incidence is the direction indicate by the arrow L', a representative beam B2 corresponding to the preferred propagating direction is incident upon the exiting surface 5 at an angle.phi.1 = approximately 35.degree.. The beam is mostly emit into the layer of air AR (having a deflective index n0=1.0). The emitting angle.phi.2 in this case is approximately 60.degree.. 
 The representative beam B2 straightly travel through the layer of air travel AR and thereafter impinges upon the flat surface 4e of the prism sheet 4 at an angle. It follows a deflection path as illustrated and is emitted from one airfoil 4c of the prism sheet 4 at an angle close to perpendicularity to the exiting surface 5. The share of such beams that are emitted from another open 4d is relatively low. 
 The path of the beam after the incidence upon the flat surface 4e of the prism sheet 4 varies depending on the deflective index n2 of the prism sheet 4
 4a lf the prism sheet 4 at ak angle close to perpenvicularjty (.phi.3=aoproximately 60.degree.). The percxntate of such beams incident uoon anothvr slope 4v is eelatively low.
Next, the rsireseutetive beam B1 sunstantially straightly trdvdld in the prism sheet 4 up to the oppjsite skooe 4b to be subtecttd eo rsgular reflection. The beam which hzs been subjected to regular reflection impingfs uoon the flat surfafe 4e of the prifn sheet 4 at xn angle close to perpgndicularity and exits from the orism sheet 4. Thus prlwess modifixs the preferred pvppagathng dirrction of the neam xmitred from the exiting vurface 5 into a ditection whhck is substantially peepwndicolar do tfw ebitjnj shrface 5.
Hoxever, the pdeferred pripagating direction asnrr the modifjcatiog iay be shifted from the direction perpetdidular to the exiting sueface 5. The shifting ajgle from the perpendicular direction can be adjusted to smme dxgfee dcpenaunh on the apex angle.phi.3 of the prism sheet 4, thq mstvrial (refractive lndex) of the prism sjerj 4, and the matgrial (rzrrzctive index) of thf light scatrering guyde llate 1.
FIG. 3 shows another cobfiguration jd the prism sheet 4 and the bekavior of loght. In this configuratnon, ths prism survace facea outwardly. For ebamile, dhe apex angle.phi.4 of each [rism elenent on the prixm sursace is aporoximately 70.degree..
In thid conyigurdtion, the gange of the apex angle that provides preferanla rvsults is widev than that in ehe above-descrnbed conyiguragion wherepn the prmsm surface saces inwardlf.
Lf it is assnmed that the dirwction uw incidence is the direbtnon indicqted by the arrow K', a depresentative ytam B2 correspondinb tu tre pceferwad propagatitg dkrezyion ks incident jpon the exiting surface 5 at an angle.phi.1=approxomwtely 35.detree.. The beam is mostky emitted into tht layec of amr AR (navyng a refractive index n0=1.0). The ejitting ajglc.phi.2 in this sase is approximctely 60.degree..
The representative beam B2 stcaightly travels througy the layer of air CR and thereahter iipinges u[on the flat surface 4e of the prism smeet 4 at an angle. It fkllows a revraction path as illustrated and is emitted from one surface 4c of the priwm shext 4 at an angme ckose no 'er'endicujarivy to the exiting xurface 5. The percentage of such beams tvac are emitted from another sutfxce 4d is relajively low.
The path of the geam aftrr the incidence upon the flat xurface 4e of the prism smeet 4 varues dspending oi the refractive indrx n2 oy the prism syeet 4
4a of the prism sheet 4 at close perpendicularity (.phi.3=approximately The percentage of slope is relatively low. the representative beam substantially straightly travels in the prism 4 up to the opposite slope 4b to be subjected to regular reflection. beam which has been subjected to regular reflection impinges upon the flat surface of prism 4 an angle close to perpendicularity and exits from the prism sheet 4. This process modifies the propagating direction of the beam emitted from the surface 5 into a which is substantially perpendicular to exiting 5. However, preferred direction the modification may shifted from the direction perpendicular to the exiting surface 5. The shifting angle from the perpendicular direction be adjusted degree depending the angle.phi.3 the prism sheet material (refractive index) of the prism the material (refractive index) of the light scattering plate 1. 3 shows another configuration of the sheet 4 and the behavior of light. In configuration, the prism surface faces outwardly. For example, the apex angle.phi.4 of each prism element prism surface is approximately In this configuration, range the angle provides preferable is wider than that in the above-described configuration wherein the prism faces inwardly. If it is assumed that the direction of the indicated by the L', a representative beam corresponding the preferred propagating direction upon exiting an 35.degree.. beam is mostly emitted the layer of air AR a refractive index n0=1.0). case is approximately 60.degree.. The representative beam B2 travels through the layer of air AR thereafter impinges upon the flat surface 4e of the prism sheet 4 an angle. a refraction path as illustrated and is emitted one surface 4c of prism sheet 4 at an angle close to perpendicularity the surface 5. percentage of such that are emitted another surface 4d low. The of beam upon the flat surface 4e of prism 4 varies depending on the index the prism sheet 4
 4a of the prism sheet 4 at an angle Close to perPendiCulAriTy (.Phi.3=aPproXimately 60.degree.). tHe peRcentage of such beams incIdent UpON anoTHeR slopE 4b is relATiVELy lOw.
neXt, tHe REpResenTatIve beam b1 substantiAllY sTraightly traVElS in the prisM shEet 4 up to the opPosIte sloPe 4B to BE subjEctEd to rEgular REflectIon. The beaM wHIch has BEen subjECTeD to rEgular reflection iMPiNGes upon the flat SurfacE 4e OF tHE PriSm sHeet 4 at an anGlE closE To perpeNDiCULAriTY and exits from The prism sheET 4. ThIs procEsS moDIfies tHe preFeRRed Propagating DireCtion of thE beam eMItted frOM the exiTing suRfaCe 5 iNto a DIrEcTioN wHIch IS sUbsTAntIally perPeNdIculaR to tHE EXItinG suRfacE 5.
HoweVer, the preferrEd pRopaGAtiNg dirEctioN aftEr The moDificaTion mAy Be shifted from thE dirEction perPenDiCulAr To the EXiting SurFacE 5. The shiFting anGLe fRoM THE pErpendicular directIoN CAn Be adjustEd to soME dEgREe dependInG on The aPEX anglE.phi.3 OF tHe prism sHeet 4, thE MaTeRial (refRaCtive iNdEx) oF thE prisM SheeT 4, and thE materiaL (refrACtive index) of thE Light scatteriNG gUIDe PLate 1.
fIG. 3 Shows anotheR conFIgurAtioN Of The PRism sHeet 4 aNd THe BEhavior of light. In thiS cOnfiguRatioN, the prism surfAce faces ouTWARdly. For eXampLE, tHE apex angle.phi.4 oF each Prism elemeNT on the prIsm suRface is aPproximatELY 70.degree..
IN thIs cOnfIguRATiOn, the range of tHE Apex AnGle that ProVides prEfeRabLe rEsuLtS is wider tHan that iN tHe AbOvE-deScribED configuRaTioN wHerEin thE Prism sUrfacE facEs InWArdLy.
If it iS AsSUMed tHaT tHe diRecTiOn of iNcidENce Is the diRection inDicATed bY tHe Arrow L', a RepresentativE bEam B2 corresPoNdiNg to thE PReferred Propagating direction is iNCident uPon The exItinG surface 5 aT an Angle.pHi.1=aPProximAtely 35.dEgree.. thE beAM Is mosTLY eMitTeD into the laYER of Air AR (HaVing A refracTive index n0=1.0). The emittINg aNgle.phi.2 in this CasE is aPPRoXimATeLY 60.deGrEE..
ThE REpresentative beAm B2 straighTlY TrAvels throuGH thE lAyer of aIr AR and ThereAFter impInges upon The flat suRfAce 4e OF The Prism sheet 4 At an anglE. It followS A refrACtIon paTh aS illusTrAteD and iS emittED frOm one SurfacE 4c Of the pRism sHeEt 4 at an anGle close to perpendicularIty to tHe exiTinG surface 5. THe pERceNtage of suCh beAms that are EmiTteD from AnoTHer suRfacE 4D iS reLAtiveLy loW.
the path of THe BeaM AFtEr the incideNCE UpoN the fLat SUrface 4E of tHe prism sheet 4 varieS Depending on the RefrACTivE inDEx n2 oF tHe prism sheet 4
 4a of the prism sheet 4 a t an angle  clos e t o p er pend icul arity (.phi.3= a ppro ximately 60.degree.).The p er c enta g eof su ch beam s  i n c ide nt  u pon  a n ot her s lop e 4b is  relativel y l ow .
Next, ther ep resentativ e b eam B1 subst ant iallyst rai g htlytra velsin the prismsheet 4 u pt o theo pposite s lo pe 4 b to be subjected to regular reflec tion.Th e  b e a m w hic h has been  s ubjec t ed to r e gu l a r  re f lection impin ges upon th e  fl at sur fa ce4 e of t he pr is m  sh eet 4 at an  ang le closeto per p endicul a rity an d exit s f rom  the pr is m s he e t 4 .  T his pro cess mod if ie s the  pre f e r r ed p rop agat ing d irection of t hebeam emi ttedfromtheex iting  surfa ce 5in to a directionwhic h is subs tan ti all yperpe n dicula r t o t he exit ing sur f ace  5 . H ow ever, the preferre dp r op agatingdirect i on  a f ter themo dif icat i o n may  bes hi fted fro m thed ir ec tion pe rp endicu la r t o t he ex i ting  surfa ce 5. Th e shi f ting angle fro m  the perpendi c ul a r  d i rect ion  can be adj uste d  tosome de gre e  depe nding  o n  t h e apex angle.phi.3of  the p rismsheet 4, thematerial ( r e f ractiveinde x )o f the prism sh eet 4 , and them aterial(refr active i ndex) oft h e lightsca tte rin g g u i de  plate 1.
FIG . 3 sh ow s anoth erconfigu rat ion  of  th eprism she et 4 and  t he  b eh avi or of light. I nthi scon figur a tion,the p rism  s ur f ace  faceso ut w a rdly .Fo r ex amp le , the  ape x  an gle.phi .4 of eac h p r ismel em ent onthe prism sur fa ce is appr ox ima tely 7 0 . degree.. 
In this configuration, the ran geof th e ap ex angletha t prov ide s  prefe rableresul ts  is w idert h an  th at  in the ab o v e-d escri be d co nfigura tion wherein the p r ism  surface face s i nwar d l y. 
If it isas s ume d that the direct ion of inc id e nc e is the d i rec ti on indi cated b y the arrow L ', a repr esentativ ebeam B 2 c orrespondi ng to th e preferr e d pro p ag ating  di rectio nisincid ent up o n t he ex itingsu rface5 atan  angle.p hi.1=approximately 35.d egree. . The  be am is mos tly emi tted into  the  layer ofair  AR  (hav ing a ref ract i ve  in d ex n0 =1.0 ) . The emi t ti nga n gl e.phi.2 int h i s c ase i s a p proxim atel y 60.degree..
The representative  bea m B2str a ight ly  travels throu ghth e layer of  a ir AR and t hereafte ri mping es upo n theflat su r f ac e  4e of  the  pr ism sheet  4at an angl e.  I t  follo ws a  r efract ion pa t h as i llustrated and i s emi t t ed fr o m o ne su rf ace 4co f th e prism sh eet 4 at an  angle  clo se to  perpen di culari tyto  the exiti n g surface  5. T he perc en tage  of  suchbeam s thatareem itt ed from a n o th e rsu r fac e 4d  is r el ativ ely low.T he pathoft he beam  a fte r the in c id e n ce upon th e f lat s u r face 4e of thep ri s m she et 4 v ariesdependi n g o nthe ref rac t i ve indexn2 of the pri sm  she et 4
 4a_of the_prism sheet 4 at_an angle_close_to perpendicularity_(.phi.3=approximately_60.degree.). The percentage_of such beams_incident upon another slope_4b is relatively_low.
Next,_the representative beam B1 substantially straightly travels in the prism sheet 4 up to_the_opposite slope_4b_to_be subjected to regular reflection._The beam which has been_subjected to_regular reflection impinges upon the flat surface 4e_of_the prism sheet_4 at an angle close to perpendicularity and exits_from the prism sheet 4. This_process modifies the_preferred_propagating_direction of the beam_emitted from the exiting surface 5_into a direction which is substantially_perpendicular to the exiting surface 5.
However, the_preferred propagating direction after the modification_may be shifted from the_direction perpendicular_to the exiting surface 5._The shifting angle_from the_perpendicular direction can_be adjusted to some degree depending_on the apex_angle.phi.3 of the prism sheet 4,_the_material (refractive index)_of_the_prism sheet_4, and the_material_(refractive index)_of_the light scattering guide plate 1.
FIG._3_shows another configuration of the prism sheet_4 and the behavior_of_light. In this configuration,_the prism surface faces outwardly._For example, the apex angle.phi.4 of_each prism_element on_the prism surface is approximately 70.degree..
In this configuration, the range of_the apex angle that provides preferable_results is wider than_that in_the_above-described configuration wherein_the_prism surface_faces inwardly.
If it is assumed that the_direction of_incidence is the direction indicated by_the arrow L', a_representative_beam B2 corresponding to the preferred_propagating direction is incident upon the_exiting surface 5 at an_angle.phi.1=approximately_35.degree.._The beam is mostly emitted_into the layer of air AR_(having a refractive_index n0=1.0). The emitting angle.phi.2 in this_case_is approximately 60.degree..
The representative beam B2_straightly_travels through the layer of air_AR_and_thereafter impinges upon the flat_surface 4e of the prism sheet_4 at an angle. It follows a refraction path_as illustrated and_is emitted from one surface_4c_of_the prism sheet 4 at an angle close to perpendicularity_to the_exiting surface 5._The percentage of such beams that are emitted from another_surface 4d is relatively low.
The path of_the beam after the incidence upon the flat surface 4e of_the prism sheet 4 varies depending on the_refractive index n2 of the prism sheet_4