COMPARISON OF VARIOUS METHODS TO MEASURE LUMINOUS INTENSITY WITH AN IMAGING COLORIMETER

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COMPARISON OF VARIOUS METHODS TO MEASURE LUMINOUS
INTENSITY WITH AN IMAGING COLORIMETER

• Ronald Rykowski
• President and Chief Technology Officer
• Radiant Imaging, Inc.
• www.radiantimaging.com
• rykowski_at_radiantimaging.com
• [phone]

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Measuring Luminous Intensity

• Background
• The Imaging Colorimeter
• Measurement of an Extended Source
• Measurement Methods
• Performance Comparison
• Measurement of a Small Source
• Measurement Methods
• Performance Comparison
• Tradeoffs

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Measuring Luminous Intensity

• Background
• The Imaging Colorimeter
• Measurement of an Extended Source
• Measurement Methods
• Performance Comparison
• Measurement of a Small Source
• Measurement Methods
• Performance Comparison
• Tradeoffs

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Background

• Market forces have created an increased need for
  luminous intensity measurement, particularly with
  LEDs and LED light fixtures.
• Research, development and production all have
  different measurement requirements
• Measurement methods are strictly specified in
  some industries, but not so in others
• Imaging colorimeters and photometers now provide
  alternatives to far-field goniometric systems
• Understanding instrument capabilities and
  limitations enables us to pick the right tool for
  a specific job

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Measuring Luminous Intensity

• Background
• The Imaging Colorimeter
• Measurement of an Extended Source
• Measurement Methods
• Performance Comparison
• Measurement of a Small Source
• Measurement Methods
• Performance Comparison
• Tradeoffs

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The Imaging Colorimeter

• Main elements include an imaging lens, a set of
  color filters, a CCD detector, and data
  acquisition and image processing
  hardware/software

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The Imaging Colorimeter

• System acquires an image of the DUT through each
  of the color filters.
• ND filters used to ensure that each color
  measurement uses the full dynamic range of the
  sensor.

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The Imaging Colorimeter

• System software automatically applies necessary
  calibrations and allows data to be manipulated
  in a variety of ways

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The Imaging Colorimeter

• Commercially available imaging colorimeters
  typically range from 10 to 16 bit dynamic range,
  3 luminance accuracy and color accuracy
  (chromaticity coordinates) 0.003

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Measuring Luminous Intensity

• Background
• The Imaging Colorimeter
• Measurement of an Extended Source
• Measurement Methods
• Performance Comparison
• Measurement of a Small Source
• Measurement Methods
• Performance Comparison
• Tradeoffs

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Measurement Methods (Extended Source)

• Goniophotometer (reference instrument)
• Imaging Colorimeter
• Two Axis Near Field Goniometer (FPMS-LI)
• Imaging Sphere

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Measurement Methods (Extended Source)

• Goniophotometer
• Source mounted on a two axis goniometer
• Stationary photometer placed in far field
• Source is rotated in two axes, allowing entire
  intensity distribution to be sampled
• Luminous intensity distribution created from
  point measurements
• Alternate configuration
• is moving mirror goniometer

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Measurement Methods (Extended Source)

• Imaging Colorimeter
• Project output from the DUT on to a screen
• Screen must be placed in that sources far field
• Screen must be large enough to capture entire
  source output
• Imaging colorimeter captures the entire
  illuminance pattern in a single quick
• measurement

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Measurement Methods (Extended Source)

• Two Axis Near Field Goniometer (FPMS-LI)
• Source mounted on a two axis goniometer
• Stationary imaging colorimeter placed in near
  field views DUT directly
• Source is rotated in two axes, allowing
  luminance measurements
• To be recorded at all angles
• Software produces model of luminance and near
  field chromaticity
• Raytracing is used to yield illuminance or
  far-field
• Intensity Data

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Measurement Methods (Extended Source)

• FPMS-LI test setup

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Measurement Methods (Extended Source)

• FPMS-LI actual measurements

At Inclination 3, Azimuth 90
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FPMS-LI Ray trace simulation
Plane at surface of source
At imaging colorimeter location
Plane at 3.4 meters
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Measuring Luminous Intensity

• Background
• The Imaging Colorimeter
• Measurement of an Extended Source
• Measurement Methods
• Performance Comparison
• Measurement of a Small Source
• Measurement Methods
• Performance Comparison
• Tradeoffs

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Performance Comparison (Extended Source)

• Luminous intensity of a sealed beam automotive
  headlamp (Philips Halogen H4701 hi beam) was
  measured with
• spot goniophotometer
• imaging colorimeter
• FPMS-LI

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Performance Comparison (Extended Source)

• Measurement parameters

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Performance Comparison (Extended Source)

• Headlamp luminous intensity
• Spot goniophotometer

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Performance Comparison (Extended Source)

• Headlamp luminous intensity
• Imaging colorimeter

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Performance Comparison (Extended Source)

• Headlamp luminous intensity
• FPMS-LI

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Performance Comparison (Extended Source)
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Performance Comparison (Extended Source)
At 3.4m from Source
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Measuring Luminous Intensity

• Background
• The Imaging Colorimeter
• Measurement of an Extended Source
• Measurement Methods
• Performance Comparison
• Measurement of a Small Source
• Measurement Methods
• Performance Comparison
• Tradeoffs

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Measurement Methods (Small Source)

• Source Imaging Goniometer (SIG)
• Performs equivalent measurement to FPMS-LI
• Source rotates in one axis and imaging
  colorimeter is mounted on a goniometric arm
• More convenient configuration for smaller
  sources

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Measurement Methods (Small Source)

• Imaging Sphere
• Optical system consists of coated, diffuse, low
  reflectance hemisphere, a curved secondary mirror
  and an imaging colorimeter

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Measurement Methods (Small Source)

• Imaging Sphere
• Source illuminates inside surface of dome, which
  acts as a curved screen
• Essentially 2p steradians of output is captured

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Measurement Methods (Small Source)

• Imaging Sphere
• Convex mirror enables the imaging colorimeter to
  image the entire inner surface of the hemisphere
  in a single exposure.

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Measurement Methods (Small Source)

• System software automatically applies necessary
  calibrations and allows data to be analyzed in a
  variety of ways

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Measurement Methods (Small Source)

• Commercially available imaging sphere has a dome
  radius of 225 mm
• This limits the systemto measuring
  smallsources, such as LEDs,since the dome
  surface must be in the far field of the source

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Performance Comparison (Small Source)

• Luminous intensity of two LEDs (Super Bright LEDs
  RL5 B2545 and Luxeon LXHL-LW5C) were measured
  with
• Imaging sphere
• SIG

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Performance Comparison (Small Source)

• Measurement parameters

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Performance Comparison (Small Source)
Luminous Intensity Measured with Imaging Sphere
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Performance Comparison (Small Source)
Imaging Sphere
SIG (goniometric)
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Performance Comparison (Small Source)
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Performance Comparison (Small Source)
RL5-X LEDs were scanned in the Radiant Imaging
SIG300 for reference purposes. Subsequently, they
were measured with the IS-LI. The 2 measurements
were examined to determine the location of the
peak intensity and the position and size of the
full-width-half-maximum (FWHM) of the light
distribution.
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Measuring Luminous Intensity

• Background
• The Imaging Colorimeter
• Measurement of an Extended Source
• Measurement Methods
• Performance Comparison
• Measurement of a Point Source
• Measurement Methods
• Performance Comparison
• Tradeoffs

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Tradeoffs

• All these instruments are capable of delivering
  high quality data for a given measurement
  requirement.
• How do you choose the best tool for a particular
  job?

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Tradeoffs

• Imaging Colorimeter (Intensity projected on
  screen)
• Advantages
• Speed
• Low cost
• Disadvantages
• Must measure in far field
• May require large screen
• Provides luminous intensity only at measured
  distance

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Tradeoffs

• FPMS-LI
• Advantages
• Delivers comprehensive data
• Measures in the near field (compact
  configuration)
• Results compatible with optical design software
• Disadvantages
• Slow speed
• Moderate cost

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Tradeoffs Imaging Sphere

• Advantages
• Speed
• High resolution
• Insensitive to output variation over time
• Small size
• Can work with ambient light
• Disadvantages
• Can only measure small sources or Condition B
  distance

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Tradeoffs

• Spot Goniophotometer
• Advantages
• High color and luminance accuracy
• Disadvantages
• Slow speed
• LED output can vary during measurement,
  especially for LEDs
• Provides luminous intensity only at measured
  distance
• Large space required for extended sources

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Tradeoffs