National Institute of Standards and Technology detector-based photometric scale
Applied Optics
|September 11, 2010
Summary
This study introduces a new method for realizing the candela, the SI base unit for photometry, using absolute detectors. This advancement significantly improves luminous intensity calibration accuracy for standard lamps.
Area of Science:
- Photometry and Radiometry
- Metrology
- Optical Engineering
Background:
- The candela, the SI base unit for luminous intensity, is crucial for light measurement.
- Traditional methods for realizing the candela relied on absolute sources, presenting limitations in accuracy.
- Improvements in detector technology offer potential for more precise photometric calibrations.
Purpose of the Study:
- To implement a novel method for realizing the candela using absolute detectors.
- To achieve a significant reduction in the expanded uncertainty for luminous intensity calibrations.
- To develop and validate reference photometers for accurate photometric measurements.
Main Methods:
- Construction of eight reference photometers utilizing silicon photodiodes.
- Matching photometers with filters to replicate the CIE spectral luminous efficiency function for photopic vision.
- Calibration and evaluation of the developed photometers for photometric applications.
Main Results:
- Successful realization of the candela using absolute detectors.
- Achieved an expanded uncertainty of 0.46% for luminous intensity calibrations.
- Demonstrated a near factor-of-2 improvement in measurement accuracy compared to previous methods.
Conclusions:
- The use of absolute detectors provides a more accurate method for realizing the candela.
- The developed reference photometers are suitable for high-precision luminous intensity calibrations.
- This advancement contributes to enhanced accuracy in the field of photometry.
Related Concept Videos
01:29Determination of Crystal Structures
In the late 1800s, the revelation that light extended beyond visible wavelengths led to the discovery of X-rays by Wilhelm Roentgen. Recognized as high-energy electromagnetic radiation with short wavelengths, X-rays prompted exploration into their interaction with crystals. Max von Laue proposed in 1912 that the periodic arrangement of atoms, ions, or molecules in crystals would cause them to diffract X-rays, a hypothesis confirmed through experiments with copper sulfate and zinc sulfide...
01:25IR Spectrometers
There are two main infrared (IR) spectrophotometers: dispersive IR spectrometers and Fourier transform infrared (FTIR) spectrometers. In a dispersive IR spectrometer, a beam of infrared radiation produced by a hot wire is divided into two parallel equal-intensity beams using mirrors. One beam passes through the sample, while another is a reference beam. The beams then move through the monochromator, which separates the radiations into a continuous spectrum of different frequencies. The...
01:30Electronic Distance Measuring Instruments
Electronic Distance Measuring Instruments (EDMs) are essential tools in modern surveying, offering precise distance measurements by emitting electromagnetic signals and calculating the time required for these signals to travel to a target and return. Two primary types of signals are used in EDMs — light waves and microwaves — each suited to specific environmental and distance requirements. Light-wave-based EDMs utilize either infrared or laser light, providing high accuracy over short distances...
01:12Instrument Calibration
Instrument calibration is essential for ensuring that instruments produce accurate and consistent results. It is vital in manufacturing, healthcare, testing laboratories, and scientific research. Calibration processes are specific to each instrument and help enhance data accuracy. Each instrument has a unique calibration process tailored to its design and function to improve data accuracy.
Analytical Balance Calibration
An analytical balance measures mass and requires regular calibration to...
Analytical Balance Calibration
An analytical balance measures mass and requires regular calibration to...
01:05Difference from Background: Limit of Detection
The limit of detection (LOD) is the smallest amount of analyte that can be distinguished from the background noise. The LOD value corresponds to the concentration at which the analyte signal is three times larger than the standard deviation of the blank signal. Below this value, the analyte signal cannot be differentiated from the background noise. It is calculated by dividing the calibration slope by 3 times the standard deviation of the blank signals.
The LOD indicates the presence or absence...
The LOD indicates the presence or absence...
01:02Flame Photometry: Overview
Flame photometry, also known as flame emission spectrometry, is a technique used for the qualitative and quantitative analysis of elements present in a sample using a flame as the source of excitation energy. The concept of flame photometry was realized in the early 1860s by Kirchhoff and Bunsen, who discovered that specific elements emit characteristic radiation when excited in flames. The first instrument developed for this purpose was used to measure sodium (Na) in plant ash using a Bunsen...