LED bianchi con nozioni di colorimetria

1. LED bianchicon nozioni di colorimetria Docente: Mauro Mosca (www.dieet.unipa.it/tfl) A.A. 2013-14 Ricevimento: alla fine della lezione o per appuntamento Università di Palermo – Facoltà di Ingegneria (DEIM)

2. L’occhio umano

3. Visione umana

4. Radiometria e fotometria - Radiometric Units physical quantities (ex. optical power) - Photometric Units the same quantities as perceived by human eye plumber’s candle a monochromatic light source emitting an optical power of (1/683) watt at 555 nm into the solid angle of 1 steradian (sr) has a luminous intensity of 1 candela (cd) - Luminous intensity

5. Fotometria a monochromatic light source emitting an optical power of (1/683) watt at 555 nm has a luminous intensity of 1 lumen (lm) - Luminous flux 1 cd = 1 lm/sr An isotropically emitting light source with luminous intensity of 1 cd has a luminous flux of 4π lm = 12.57 lm.

6. Fotometria luminous flux incident per unit area. Measured in lux - Illuminance 1 lux = 1 lm/m2

7. Fotometria ratio of the luminous intensity emitted in a certain direction (measured in cd) divided by the projected surface area in that direction (measured in m2). The luminance is measured in cd/m2 - Luminance (of a surface source) If the direction of interest is normal to the chip surface, the luminance is the luminous intensity emitted along the chip-normal direction divided by the chip area Luminance of lambertian LEDs is a constant, independent of angle

8. Radiometria e fotometria Riepilogando…

9. Curva di sensibilità dell’occhio umano

10. Curva di sensibilità dell’occhio umano

11. Efficacia ed efficienza luminosa flusso luminoso curva sensibilità dell’occhio umano densità spettrale di potenza

12. Efficacia ed efficienza luminosa

13. da ricordare…

14. Colorimetria: funzioni color-matching CIE has standardized the measurement of color by means of color-matching functions and the chromaticity diagram Human sense of vision is very different from the human sense of hearing color-matching functions con

15. Colorimetria: funzioni color-matching tricromaticità non sono uniche!!

16. Colorimetria: valori di tristimolo For a given power-spectral density P(l), the degree of stimulation required to match the color of P(l) is given by TRISTIMOLO valori di

17. Colorimetria: coordinate cromatiche Each tristimulus value represents the approximate (but not exact) degree of stimulation that each type of retinal cone experiences when illuminated by a light source with spectrum P(l) coordinate cromatiche stimulation of each primary light (or of each type of retinal cone) divided by the entire stimulation ( X + Y + Z )

18. Diagramma di cromaticità

19. Diagramma di cromaticità colori monocromatici

20. Diagramma di cromaticità equal energy point (X=Y=Z) distribuzione spettrale costante

21. Diagramma di cromaticità: ellissi di MacAdam the geometric distance between two points in the (x, y) chromaticity diagram does not scale linearly with the color difference total number of differentiable chromaticities can be obtained by dividing the area of the chromaticity diagram through the average area of the MacAdam ellipses this calculation yields the result that humans can discern approximately 50 000 distinct chromaticities

22. Diagramma di cromaticità uniforme it is very desirable for the color difference to be proportional to the geometric difference

23. Coordinate cromatiche uniformi tanto per la cronaca…

24. Lunghezza d’onda dominante e purezza di colore dominant wavelength color purity 100%??? lo spettro della sorgente si allarga

25. LED nel diagramma di cromaticità close to on the perimeter spectral linewidth of about 1.8 kT

26. Colore e cromaticità • A color is defined by its location in the chromaticity diagram (i.e. by its chromaticity) • The CIE’s definition of color includes chromaticity as well as brightness • The CIE’s definition of the color of light is given by the dominantwavelength, saturation, and brightness • The color of an object is given by the dominant wavelength, saturation, and lightness

27. Lo spettro solare Planckian black-body radiation spectrum forms a unique and very useful standard for white light because it allows to describe the spectrum with only one parameter: the color temperature Natural daylight closely resembles the planckian spectrum but…

28. Radiazione di corpo nero di Planck legge di Wien

29. Luogo geometrico di Planck

30. Temperatura di colore e temperatura di colore correlata • Color temperature of a white light source, given in units of kelvin, is the temperature of a planckian black-body radiator that has the same chromaticity location as the white light source considered • The correlated color temperature of a white light source is defined as the temperature of a planckian black-body radiator whose color is closest to the color of the white light source and if the white light does not lie on the planckian locus???

31. Temperatura di colore e temperatura di colore correlata P.S. I colori caldi non hanno niente a che fare con la temperatura di colore!!

32. Sintesi (color mixing) additiva How to determine the chromaticity coordinates of the mixture of three discrete emission bands?

33. Sintesi additiva dove: linear combination of the individual chromaticity coordinates

34. Color gamut color gamut (per tre LED RGB) (per tre fosfori standard RGB) (sRGB simile a NTSC)

35. Resa del colore (color rendering) The ability to render the colors of an object is measured in terms of the color-rendering index or CRI a measure of the ability of the illuminant (i.e. a white illumination source) to faithfully render the colors of physical objects illuminated by the source

36. Indice di resa cromatica (Color Rendering Index – CRI) The color-rendering ability of a test light source is evaluated by comparing it with the color-rendering ability of a reference light source • Choice of the reference source: • planckian black-body radiator with the same color temperature as the test source (if the test source is located on planckian locus) • planckian black-body radiator with the same correlated color temperature as the test source (if the test source is not located on planckian locus) • CIE standard illuminant

37. Indice di resa cromatica (Color Rendering Index – CRI) The planckian black-body reference source is assumed to have perfect color rendering properties (CRI = 100) special CRI

38. CRI

39. Colore e cromaticità

40. CRI

41. CRI PICCOLO TEST Is it possible for two physical objects of different colors to appear to have the same color under certain illumination conditions? What is the color of a yellow banana when illuminated with a red LED? What is the color of a green banana when illuminated with a yellow LED?

42. Generazione di luce bianca con LED COLOR RENDERING E F F I C I E N Z A

43. Generazione di luce bianca con LED linea del porpora (no colori spettrali)

44. Calcolo efficacia luminosadi un LED dicromatico

45. Efficacia luminosa di un LED dicromatico

46. LED dicromatici monolitici • Different approaches: • using two LEDs (blue and yellow) • using a semiconductor (e.g. AlGaInN) as a wavelength converter • using co-doping • using different quantum-wells • using phosphors as wavelength converters

47. h e LED dicromatici monolitici

48. LED tricromatici

49. Efficacia luminosa di LED tricromatici Dl= 5kT

50. Efficacia luminosa di LED tricromatici Dl= 8kT