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In photometry, luminous intensity is a measure of the wavelength-weighted power emitted by a light source in a particular direction per unit solid angle, based on the luminosity function, a standardized model of the sensitivity of the human eye. The SI unit of luminous intensity is the candela (cd), an SI base unit.
It involves the automatic constriction and dilation of the pupils in response to changes in light intensity or accommodation. With an automated pupillometer and an algorithm analyzing the pupil continuously for 5 seconds, the Quantitative Pupillometry Index (QPi) can measure pupillary reactivity and provides a numerical value.
Troland does not directly convert to other units, being a retinal luminance per unit area of a pupil. However Troland is linked to retinal illuminance in lux = lm/m 2 as follows. Assuming the corneal luminance L from an extended source, the pupil diameter p and the focal length of the eye F, the retinal luminance is:
The lumen is defined as amount of light given into one steradian by a point source of one candela strength; while the candela, a base SI unit, is defined as the luminous intensity of a source of monochromatic radiation, of frequency 540 terahertz, and a radiant intensity of 1/683 watts per steradian.
Luminous flux (in lumens) is a measure of the total amount of light a lamp puts out. The luminous intensity (in candelas) is a measure of how bright the beam in a particular direction is. If a lamp has a 1 lumen bulb and the optics of the lamp are set up to focus the light evenly into a 1 steradian beam, then the beam would have a luminous ...
The template will not display the string "Table X. " in front of the table's title "SI photometry units". 1 = <number> The template will display the table number as part of the table header in the following form: "Table <number>. SI photometry units.", where <number> is a placeholder for the number (or other table designation) given as parameter.
Traditional clinical pupillometers measure pupil size using infrared cameras in specialized hardware. Software pupillometers measure pupil size using a smartphone camera and light source. Several studies have demonstrated that software based pupillometers have comparable accuracy to dedicated hardware pupillometers.
Stiles, along with his fellow National Physical Laboratory researcher Brian Hewson Crawford, set out to measure the effect of light intensity on pupil size. They constructed an apparatus where two independently controlled beams, both emitted by the same light source, entered the eye: a narrow beam through the center of the pupil, and a wider ...