VI. Terminology for Display

Transcription

1 Special Topics in Display Technology 1 st semester, 2015 VI. Terminology for Display * Reference books: [Light Measurement Handbook] ( [ 응용광학 ] ( 두양사 ) 21 장

2 Radiometry and Photometry Luminous Flux Luminous Exitance Illuminance Luminous Intensity Luminance Several Aspects of Photometry Inverse Square Law Lambertian Surface Viewing-Angle Properties Measurement Luminous Flux Illuminance Contents

3 Radiometry and Photometry radiometry: a set of techniques for measuring electromagnetic radiation, including visible light. Radiometric techniques characterize the distribution of the radiation's power in space, as opposed to photometric techniques, which characterize the light's interaction with the human eye. photometry: the science of the measurement of light, in terms of its perceived brightness to the human eye. It is distinct from radiometry, which is the science of measurement of radiant energy (including light) in terms of absolute power. In photometry, the radiant power at each wavelength is weighted by a luminosity function that models human brightness sensitivity. Typically, this weighting function is the photopic sensitivity function, although the scotopic function or other functions may also be applied in the same way.

4 [Light Measurement Handbook] (

5 Solid Angle 2-dimensional angle 3-dimensional solid angle r q l q l r (radian) The solid angle is the angle in the 3- dimensional space that an object subtends at a point. It is a measure of how big that object appears to an observer looking from that point. da d (steradian, sr) 2 r 2 da 4 r total 2 2 r r Surface 4 (sr)

6 The nonpoint and/or nonuniform light sources may be treated as composed of small differential point sources, or the entire source can be observed at a large distance so that its luminous flux may be considered as radiating from a point. [Examples] (1) If we look at the moon from the earth, what is the solid angle formed by our eyes and the area of the moon? (2) Consider that an incandescent lamp is hung down from a ceil. The height of this lamp is 2 m. If we can assume this lamp to be a point source, what would be the solid angle formed by this lamp and the book you are holding by your hands. The area of the book is 30cm*40cm.

7 복사측정학 Luminous Flux f e (radiant flux): radiant energy per unit time, also called radiant power. (W) 측광학 f v (luminous flux or luminous power): the measure of the perceived power of light. It differs from radiant flux, the measure of the total power of light emitted, in that luminous flux is adjusted to reflect the varying sensitivity of the human eye to different wavelengths of light. 555 nm, 1W lm luminous efficacy: luminous power per unit input power (lm/w) [Example] (1) 1 lm of the light at 555 nm equals to 1/683 W. What is the watt of 1 lm at 630 nm? (2) We have three lasers of which the wavelengths are 450 nm, 555 nm, 650 nm. If the output power of each lasers is 10 W, what is the total lumen?

8 Luminous Exitance M (exitance): power emitted from a unit surface. 복사측정학 radiant exitance: radiant power emitted from a unit surface. M e = f e / A (W/m 2 ) 측광학 luminous exitance: luminous power emitted from a unit surface. M v = f v / A (lm/m 2 )

9 Illuminance 복사측정학 E (irradiance): radiant power incident on a unit surface, also called radiant flux density. E e = f e / A (W/m 2 ) 측광학 E (illuminance): luminous power incident on a unit surface, also called radiant flux density. Irradiance E v = f v / A (lm/m 2 = lux (lx))

10 Luminous Intensity 복사측정학 radiant intensity: radiant power per unit solid angle. (W/sr) I e = f e / w (W/sr) (w: solid angle) 측광학 luminous intensity: luminous power per unit solid angle. (lm/sr = candela) I v = f v / w (lm/sr = cd)

11 Luminous Intensity Distribution Incandescent lamp LED: NSCW 215T (Nichia Co.Ltd)

12 Example luminous flux? illuminance? 1 m 1 cd illuminance? 2 m 60 o area: 100 cm 2

13 Luminance 복사측정학 radiance: radiant power per unit solid angle per unit projected source area. 측광학 L e = f e / (Acosq) w = I e / Acosq (W/sr*m 2 ) luminance: luminous flux per unit solid angle per unit projected source area. L v = f v / (Acosq) w = I v / Acosq (lm/sr*m 2 =cd/m 2 =nit) n q di L df 2 d d f dw di L d w da da cosq da cosq p da da p dacosq

14 Typical Luminance Values source Typical luminance values luminance level (candelas/square meter) Sun 1,550,000,000 Moon 2,500 Candle 10, W incandescent lamp 12, W fluorescent lamp 8,200 Zenith sky 1,100 Snow in sunlight 31, W tungsten filament 11,600,000 High pressure mercury arc 1,600,000 [Illuminating Engineering] (J. B. Murdoch, 2 nd ed.)

15 The Inverse Square Law The illuminance is proportional to the intensity and inversely proportional to the square of the distance from the source. The total luminous flux from a point source (intensity = I) is f = 4 I. The area of a sphere of which the center is coincident with the point source and the radius is d is A=4 d 2. Therefore, the illuminance on the inner surface of the sphere is E= 4 I/4 d 2 = I/d E I / d LS / d L b d [Light Measurement Handbook] ( E I cos b 2 d

16 Point Source Approximation five times rule : the distance to a light source should be greater than five times the largest dimension of the source at which the error is ~ 1% compared to the prediction from the inverse square law. [Light Measurement Handbook] (

17 General Inverse Square Law for a point source; d Idw IdA'cos b 2 d assumed to have a luminance L in the direction of point P d Icos b E da 2 ' d [Illuminating Engineering] (J. B. Murdoch, 2 nd ed.) d is large enough compared to the dimension of the source. for an element of an area source; di cos Lcos cos da de b b 2 2 d d I L cos da E S S L cos cos bda 2 d

18 [ 코사인제 3 법칙 (cosine-third law)] 점광원에서방출된빛이표면과의수직방향에대해 q 의각도를이루며입사할경우, ' E I cos q / d I cos q / d / cosq I cos q / d ( )

19 Example 15 cm a flat circular lamp 15 cm in diameter intensity? 2 m illuminance? b 3 m a table [Illuminating Engineering] (J. B. Murdoch, 2 nd ed.)

20 Polar Plot of Luminance The polar plot of angular distribution of luminance contains all information about luminance distribution on an emitting surface. A point on the polar plot indicates one particular viewing direction along which the luminance is measured. The luminance value is normally expressed by a specific color.

21 Example of the Polar Plot <edge-lit backlight>

22 Viewing-angle Characteristics of Emitting Surfaces Angular distribution of luminance measured on a direct-lit BLU * Figures: G.J. Park, IDW 06 Digest, p.953 (2006) TV 용직하형 BLU side lobe

23 Lambertian Surface Lambertian surface has a constant luminance for any viewing angle, i.e. the same apparent brightness to human eyes. Many diffuse surfaces are Lambertian such as the surface of white paper or the emitting surface of the moon. The Lambertian surface has a simple relation between the luminance and luminous exitance. luminance (cd/m 2 ) Lambertian distribution 0 o viewing angle ( o ) [Light Measurement Handbook] (

24 Lambert s Cosine Law ( q) cos I I m q L ( q ) ( q ) I I m constant Acosq A A p I q L q q 2 / 2 f I( q ) d LA d dq cosq sinq LA A fa M L A 0 0

25 Example Luminous exitance? luminous flux? intensity? q EXPERIMENTAL SQUARE FLUORESCENT LIGHT (GE, 1959) an 8-cm square Lambertian flat light source with a luminance of 500 cd/m 2

26 <Gonio-photometer> Measurement: Luminous Flux I Zonal lumens o ( ) ( ) 2 sin 2 I ( q )( cosq1 cosq2) I ( q ) ZC df I q dw I q qdq q q o I ( q ) ZC q q 1 2 q q 1 2 [Illuminating Engineering] (J. B. Murdoch, 2 nd ed.) 2 / 2 I( q, ) d d dq I( q, )sinq 0 0

27 double-axis Gonio-photometer Measurement Examples [Illuminating Engineering] (J. B. Murdoch, 2 nd ed.) [IESNA Lighting Handbook] (IESNA, 9 nd ed.)

28 Measurement: Luminous Flux II <Ulbricht Sphere> direct illuminance + indiredt illuminance Luminance L da lumens illuminance meter small shield de da at point X Y Y LdAcos d 2 q LdA 4r 2 2 independent of the position of Y! The indirect illuminance is uniform throughout the sphere. uniform reflectance r The sphere is calibrated by measuring a standard source whose total lumen output is known, and whose spatial and spectral properties are similar to lamps being measured. [Illuminating Engineering] (J. B. Murdoch, 2 nd ed.) Total reflected lumens illuminance due to reflected lumens 2 ( 1 ) refl. r r r 1 r E 2 4 r 1 r r ( r)

29 [IESNA Lighting Handbook] (IESNA, 9 nd ed.) From Wikipedia, the free encyclopedia

30 Measurement Example * 김일호 (LMS), [BLU 광학특성평가 ] ( 인하대 OTEC)

31 Measurement: Luminous Intensity beam candela 측정 : representative of the candela at the peak intensity of the beam mm * 김일호 (LMS), [BLU 광학특성평가 ] ( 인하대 OTEC)

32 [example] q total flux=0.1 lm A: q=10 o 4.2 cd B: q=5 o 16.7 cd [Light Measurement Handbook] (

33 Measurement: Luminous Intensity * 김일호 (LMS), [BLU 광학특성평가 ] ( 인하대 OTEC)

34 Common Photometric Quantities, Units, and Symbols Symbol Name Unit Abbreviation flux lumen lm I luminous intensity candela cd = lm/sr L luminance nit (deprecated, nit is not approved for use anymore) cd/m 2 E illuminance lux lx = lm/m 2 M luminous exitance (do not use lux) lm/m 2