Wat is licht, wat is meten? Belgisch Perspectief! Spectraal of niet-spectraal meten: that s the question IGOV kenniscafé Arnhem, 31 oktober 2013 Peter Hanselaer
Light&Lighting Laboratory Introduction Spectral integrated measurements Working principles Pro and contra Outline Spectral resolved measurements Working principles Calibration Bandwidth Stray light 2
Light&Lighting Laboratory The team 3 3
Lighting Light&Lighting Laboratory Topics Optical design Measurement Facilities Appearance New Light Sources 4
PhD research items LEDs and general lighting OLED remote phosphor LEDs lighting in the operating room colour rendering gloss perception colour appearance ray tracing scattering and fluorescence spectral response solar cells Light&Lighting Laboratory Activities Industrial consultancy consortium >70 companies Bilateral projects Projects with non-profit organisations Measurements Innovation support Courses Lectures 5
Combining research with consultancy PhD Research Light&Lighting Laboratory Mission Education Society Industrial Consultancy 6
Light&Lighting Laboratory: Measurement facilities Spectrometers/ CCD detectors 7
Light&Lighting Laboratory: Measurement facilities Near field goniometers LID Ray files 8
Introduction 9
Introduction To measure, to see 10
Introduction Spectral data Spectral radiometric quantity (W...) X e,λ At least 80 numbers! UV 380 780 IR λ( nm) 11
Introduction Photometric quantities 780 Φ = 683. Φ. V( λ). dλ lumen 380 780 e, λ E = 683. E. V( λ). dλ lux 380 780 e, λ L = 683. L. V( λ). dλ cd / m 380 e, λ Φ e, λ 2 Eye sensitivity Spectrum of the stimulus UV 380 780 IR λ ( nm ) 12
780 X = k. L ( λ). x( λ). dλ 380 780 e, λ Y = k. L ( λ). y( λ). dλ 380 780 e, λ Z = k. L ( λ). z( λ). dλ 380 e, λ Relative Energy z y x 400 500 600 700 Wavelenght (nm) Φ e, λ 2 Observer (1931) 10 Observer (1964 ) Introduction Colorimetric quantities Colour matching Spectrum of the stimulus UV 380 780 IR λ ( nm ) 13
780 " Number " = k. (spectral quantity).(standardized function). dλ 380 Introduction Spectral resolved or spectral integrated Direct measurement using filters and a photodiode Spectroradiometer: measurement of spectrum using a dispersive element and a detector; numerical evaluation of the integral 14
Spectral integrated measurements 15
Spectral integrated measurements Filters 780 Response S = k. Φ e, λ( λ ). τ ( λ ). R( λ ) d λ τ( λ) : transmittance of filter R( λ) : responsivity of detector 380 Φ = 780 683 Φ λ( λ ). ( λ ) λ 380 e, V d 16
Spectral integrated measurements Filters Filter engineering: particular combinations of coloured glass 17
Spectral integrated measurements Quality of filter Relative Response 1.0000 0.1000 0.0100 0.0010 0.0001 CIE Photopic Luminosity Function 0.0000 400 500 600 700 Wavelength (nm) f ' 1 with s * r = = s s r. * r y dλ ydλ S. y. dλ A S. s. dλ A r Quality assessment using f 1 Calibration for illuminant A f 1 preferentially < 1.5% (DIN classes) 18
Introduction: colour and numbers Spectral integrated measurements Disadvantages Calibration based on illuminant A; white LED? Low accuracy of colour matching filters in the tails: monochromatic LED? 3 filters required for colour No determination of the CRI Relative Energy z y x 2 Observer (1931) 10 Observer (1964 ) 400 500 600 700 Wavelenght (nm) 19
Introduction: colour and numbers BUT easy to use! Spectral integrated measurements Advantages Commercial tristimulus instrument Commercial illuminance meter 20
Spectral resolved measurements 21
Introduction: colour and numbers Array detector Pixels Spectral resolved measurements Principles P Wavelength Dispersive element: prism or grating 22
Introduction: colour and numbers Spectral resolved measurements Spectrometer 23
Introduction: colour and numbers Spectral resolved measurements Spectrometer Source: Ocean Optics 24
Considerations: Wavelength calibration Power Calibration Bandwidth Stray light Second order filters CCD saturation Integration time Dark current correction Spectral resolved measurements Spectrometer 25 25
Wavelength calibration Pixelcolumn N versus wavelength (linear, parabolic, higher order) 2 3 λ = C0 + C1. N + C2. N + C3. N Spectral resolved measurements Spectrometer λ( nm) Check: wavelength calibration lamp (Hg, He) pixel Power calibration counts/sec versus spectral radiance, spectral intensity or spectral irradiance standard; cooled CCD 26
Spectral bandwidth Spectral resolved measurements Bandwidth IN OUT E E e,λ e,λ BW Wavelength (nm) Wavelength (nm) Wavelength step is not the same as bandwidth! Bandwidth preferentially smaller than 5 nm 27
Spectral resolved measurements Bandwidth correction Correction possible applying deconvolution 28
Introduction: colour and numbers Determined by Resolving power of grating; trade off with wavelength range Dimensions of the spectrometer Input slit width; trade off between signal strength and bandwidth Array detector Spectral resolved measurements Bandwidth Dispersive element 29
Stray Light Array detector Spectral resolved measurements Stray Light Stray light Scattering Dispersive element Stray light response depends on light source, instrument and SR! 30
Introduction: colour and numbers Spectral resolved measurements Stray Light UV irradiation of a halogen lamp Input: UV versus red ratio: 1:100 Stray light: 1% Responsivity detector: UV versus red ratio: 1:10 Stray light signal = 10x UV signal 31
Spectral resolved measurements Stray Light Solutions: double monochromator, filters, correction matrix, f/# match 32
Introduction: colour and numbers Spectral resolved measurements Popularity Spectral instruments have become very popular Cheap CCD or array detectors Fibre coupling Compact with acceptable bandwidth CCD partially coated with second order filters 33
www.lichttechnologie.be: daar brandt de lamp... 34