LED Fundamentals Radiometry & Radiometry & Photometry 08-03-2011
Jun 25, 2015
LED Fundamentals
Radiometry &Radiometry & Photometry
08-03-2011
Definitions, Units and Symbols
Radiometry – deals with the detection and measurement of electromagnetic radiation across the total spectrum
Photometry – subfield of radiometry; radiometric power scaled by the spectral response of the human eye
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Definitions, Units and Symbols
Radiometry – deals with the detection and measurement of electromagnetic radiation across the total spectrum
Photometry – subfield of radiometry; radiometric power scaled by the spectral response of the human eye
Radiometric PhotometricQuantity Symbol Units Quantity Symbol Units
Radiant Power Φe W Luminous Flux Φv lumens (lm)Radiant Intensity Ie W/sr Luminous Intensity Iv lm/srRadiant Intensity e W/sr Luminous Intensity v lm/sr
Irradiance Ee W/m2 Illuminance Ev lm/m2
Radiance Le W/m2-sr Luminance Lv lm/m2-sr
“e” = “energetic”
“v” = “visual”
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v = visual
Converting to Photometric Units
Power (Watts) is converted to luminous flux (lumens) via the relation:
780 Φv = flux (lumens)
380
dVPK evPe = Power
V = photopic response function of the human eye1
K = constant (683 lm/W for photopic)
0.7
0.8
0.9
ty
0.4
0.5
0.6
Rel
ativ
e Se
nsiti
vi
0
0.1
0.2
0.3R
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0400 450 500 550 600 650 700 750
Wavelength (nm)
Convert Radiometric to Photometric
eP V vP
0 4
0.6
0.8
1
ensi
ty [a
.u.]
0.4
0.6
0.8
1
0.4
0.6
0.8
1
0
0.2
0.4
400 450 500 550 600 650 700 750
Wavelegth [nm]
inte
0
0.2
400 450 500 550 600 650 700 750
W aveleng t h ( nm)
0
0.2
400 450 500 550 600 650 700 750
W aveleng t h ( nm)
780
380
dVPK ev
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Solid Angle
Surface Area = A
Sphere radius = R
2Solid Angle Ω = A/R2
Units: Steradians (sr)
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Projected Solid Angle
)( area angle Solid d d Area Angle Solid
)(cosanglesolid projected of Aread ) (cos angle solid d
Unit sphere
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Unit sphere
Projected Solid Angle
sin ddd
2
cos
proj dd
00
sincos proj ddα
2sin j sin proj
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Photometric Units and SymbolsPhotometric Units
Quantity SymbolMetric Units Name
English Units Name
Luminous Flux Φ lumens (lm) lumens
Luminous Intensity I lm/sr
candela (cd) or
candlepower
Illuminance E lm/m2 lux (lx) lm/ft2 Ft-candleLuminance L cd/m2 nits cd/π*ft2 Ft-Lambert
II EL
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Lambertian Source
Brightness (luminance) is independent of angle 0LL
Intensity falls off as cosθ cos)( 0II Many LEDs are very nearly
Lambertian sources0I
cos0I
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Lambertian Source
Total flux in a 2θ cone:Total flux in a 2θ cone:
''sin'2
dI ''sin'20
dI
''sin'cos2
20
0 dI sin2
0 I
lumens.is cd1ofsourceLambertian a offlux totalThe
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Disclaimer
All information contained in this document has been checked with the greatest care. OSRAM Opto Semiconductors GmbH can however, not be made liable for any damage that occurs in connection with the use of these contentsthat occurs in connection with the use of these contents.
OSRAM Opto Semiconductor GmbH makes no representations and warranties as to a possible interference with third parties' intellectual property rights in view of products originating from one of OSRAM Opto Semiconductor GmbH's partners, or in view of products being a combination of an OSRAM Opto Semiconductor GmbH's product and a product of one of OSRAM Opto Semiconductor GmbH's partners Furthermore OSRAMproduct of one of OSRAM Opto Semiconductor GmbH s partners. Furthermore, OSRAM Opto Semiconductors GmbH cannot be made liable for any damage that occurs in connection with the use of a product of one of OSRAM Opto Semiconductor GmbH's partners, or with the use of a combination of an OSRAM Opto Semiconductor GmbH's
f f OS O S Gproduct and a product of one of OSRAM Opto Semiconductor GmbH's partners.
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