Cooke Radiometric Description
Radiometry is a broad field encompassing all techniques for measuring electromagnetic radiation, including the measure of visible light. These techniques measure the distribution of the radiation’s power in space. This field includes photometry, which more specifically measures attributes of electromagnetic energy that are visible to the human eye. Instruments in this category address both the broad and more specific attributes of light these fields cover.
Chroma Meters (or color meters) primarily measure chromaticity, which is the quality of a color. Chromaticity is a measurement of hue and colorfulness; colorfulness in this case can also be referred to as chroma and defines the difference between a color and gray. Many chroma meters can measure other parameters as well, including illuminance, color temperature, dominant wavelength, and excitation purity. Certain Minolta meters also offer special features specifically for accurate measurement of white light and LED lights. Minolta also offers meters for specifically measuring the color of certain foods, such as tomatoes and coffee.
Key Features of Chroma Meters
Aperture Size. This is the size of the opening that all light being measured by a meter must pass through. A larger opening means the meter can measure a larger area at one time. Many sizes are offered, including 8, 40, 45, and 50mm
Color Detector. Typically silicon photo cells are used, sometimes with multiple cells per meter; however some Gigahertz-Optik meters utilize a radiance sensor with an integrated diode array spectrometer
Self-Calibration. This feature allows users to recalibrate their own meters. It is present in many meters and saves the user time and money that would otherwise have been spent on professional recalibration
LCD Color Analyzers
An LCD Color Analyzer is a tool used to analyze the color luminance produced by LCD, EL, and Plasma displays. These meters are also useful for white balance, chromaticity adjustment, and inspection of flat panel displays during production. Some units can also measure gamma characteristics and flicker. With the growing popularity of LEDs, many meters are now capable of measuring LED light accurately which was previously never possible due to varying spectral emission distribution produced by LEDs. Meters today are faster and can measure in lower luminance than ever before.
Key Features of LCD Color Analyzers
Lowest Luminance. It is important to know the lowest luminance an LCD color analyzer can measure. Minolta meters can measure extremely low luminance as low as 0.005 cd/m2
Measurement Speed. Some meters can measure a maximum of 4 times per second at low luminance and 20 times per second at normal luminance levels
Measurement Angle. A narrow measuring angle will ensure correct reading on non-uniform display systems. Some meters incorporate a special optical design that eliminates the influence of measuring angle dependency
LED Analyzers measure the luminous flux of LED lights. This means that the unit measures the total visible energy emitted by a light source. Typically, these incorporate a sphere in which the light source to be measured is placed; the sphere focuses all the power emitted from the light source directly on the detection component. Gigahertz-Optik offers analyzers with a range of different sphere sizes to meet any need.
Light Meters / Illuminance Meters
An Illuminance Meter measures how much a given incident light illuminates a surface, unlike a luminance meter, which measures the light being emitted from a particular area. Many illuminance meters do also function as luminance meters given they use certain attachments.
Illuminance is basically another word for brightnes. However the term brightness should not be used for quantitative description. Therefore we say illuminance. Today illuminance meters can effectively measure most types of visible light.
Key Features of Light Meters / Illuminance Meters
Measuring Modes. Some meters can measure Illuminance, illuminance difference, average illuminance, illuminance ratio, integrated illuminance, and integration time. Most other meters can measure in a maximum of five modes and many often require special attachments to measure in certain modes.
Accuracy Classification. Meters are classified by DIN and JIS standards.
Class L and Precision are the highest classes in each, respectively. A higher class translates to greater accuracy. However, it will also mean a higher price.
DIN classes: L, A, B, C
JIN classes: Precision, AA, A, B
Illuminance Range. Most meters typically have a maximum range of 199,900 lx
Luminance is a photometric measurement of the luminous intensity of light travelling in a given direction. In other words, it describes the amount of light that passes through or is emitted from a particular area at a particular solid angle. This type of measurement is especially useful because it quantifies the properties of light that the human eye actually perceives. Measuring these quantities of light is essential, for example, for TV studios, sports arenas, emergency situation lighting, traffic lighting, and automobile lighting.
Key Features of Luminance Meters
Measuring Method. Luminance meters can measure either with contact or from a distance. Many can perform both, but some can only do one or the other, so choose wisely based on your needs.
Measuring Modes. Luminance meters can measure several attributes of luminance. Typically units can measure luminance, luminance ratio, and peak luminance/luminance ratio. However, some units can measure more; for example, Gossen offers a meter that can measure 5 different modes.
Luminance Range. This is simply the range of values a luminance meter can measure. This range differs depending on measuring angle. Certain Minoltameters can measure up to 999,900cd/m²; this is relatively high compared to other meters.
A Spectroradiometer measures spectral power distribution (light energy) of a light source at any specific wavelengths across the entire electromagnetic spectrum. These quantities of spectral power distribution include both radiometric and photometric, or invisible and perceived electromagnetic quantities (illuminance/irradiance, luminance/radiance, etc.). These units are used to categorize and organize types of lighting based on these characteristics.
Spectroradiometers are also the most accurate instruments for describing color. This is because knowledge of the specific spectral power distribution of a light will always refer to a specific color, whereas color/color temperature measurements do not necessarily refer to the same spectral power distribution. Spectroradiometers are also used to calibrate LCD and CRT displays and ensure that color is displayed correctly in these displays.
Key Features of Spectroradiometers
What is the difference between Spectroradiometer and Spectrophotometer?
Lens Type. Typically lenses are either standard or macro. Macro lenses feature the ability to measure a smaller area and a smaller minimum measuring distance
Measuring Area/Distance. A smaller measuring distance and area allow for more specific measurements of spectral properties
Luminance Range. Luminance is a measure of how much light is being emitted from a particular area, falling within a particular solid angle. A larger range will allow for measuring of brighter and dimmer light sources. This depends on measuring angle.
Measuring Angle. A spectroradiometer also uses the angle of light to make measurements. Some units can measure angles that are extremely small (less than one quarter of a degree).
Spectroradiometers and Spectrophotometers have similar sounding names but different purposes. A spectroradiometer is concerned with measuring the spectral power distribution (light energy), while spectrophotometers are instruments for measuring the color of light. Spectrophotometers provide high accuracy and the ability to measure absolute colors. TEquipment carries both. Find them here
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A UV Meter is a tool for measuring ultraviolet irradiance. UV Meters measure the radiometric value of power of ultraviolet radiation. This is different from a luminance or illuminance meter; these meters measure photometric qualities of light.
UV Meters are useful for meeting radiometry and laboratory requirements, UV-curing in off-set printing, lamp UV intensity and aging, industrial process monitoring, semiconductor fabrication, prevention of skin damage, sterilization, and environmental monitoring.