Basic Principles of Light Measurement

Tarrant, A.W.S.

doi:10.1016/b978-0-12-215840-7.50006-9

Cited by 3 publications

(2 citation statements)

References 3 publications

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“…It is conventionally considered ideal if D(α, λ), at a particular wavelength, matches a cosine response, such that D(α, λ) = cos(α), since this is characteristic of the angular variation of intensity when light is incident at an angle on a flat surface, such as is approximated by the skin (Tarrant 1989). In practice, many meters deviate significantly from cosine response (Martin et al 1999).…”

Section: Angular Correction Factormentioning

confidence: 99%

Traceable calibration of ultraviolet meters used with broadband, extended sources

1999

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A calibration system has been developed to provide increased accuracy in the measurement of the irradiance responsivity appropriate for UV meters used with broadband, extended sources of the type employed in phototherapy. The single wavelength responsivity of the test meter is obtained in the wavelength range 250-400 nm by intercomparison with a transfer standard meter in a narrow, monochromatic beam. Traceability to primary standard irradiance scales is provided via the National Measurement System with a best uncertainty of 7% (at 95% confidence). The effective responsivity of the test meter, when used with broadband extended sources, is calculated using the measured spectral and angular response of the meter and tabulated data on the spectral and spatial characteristics of the source radiance. The uncertainty in the effective responsivity, independent of the source variability, is estimated to be 10% (at 95% confidence). The advantages of this calibration system over existing approaches are discussed.

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Section: Angular Correction Factormentioning

confidence: 99%

Traceable calibration of ultraviolet meters used with broadband, extended sources

1999

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“…The response of a radiometer depends upon the range of wavelengths present in the incident light, the radiance of the source and the direction from which the light is incident upon the entrance aperture of the detector. For a true measurement of irradiance, the directional response D of the radiometer should vary as the cosine of the angle α between the incident light and the axis of the detector input optics (Coleman et al 2000, Tarrant 1989). In practice, D may also be a function of both the azimuthal angle θ and wavelength λ, and D(α, θ, λ) may be a good or poor approximation to an ideal cosine response.…”

Section: Introductionmentioning

confidence: 99%

A study of the directional response of ultraviolet radiometers: I. Practical evaluation and implications for ultraviolet measurement standards

Pye

Martín

2000

Phys. Med. Biol.

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The directional responses of a range of ultraviolet radiometers commonly used for irradiance measurements of UVB and UVC have been studied. Radiometers with 24 diffuser/filter combinations were assessed using a deuterium source, and three different diffuser/filter designs were assessed using a monochromatic source. The directional responses of the radiometers have been calculated and expressed in terms of figures of merit similar to those described for (photopic) illuminance meters in BS 667 and CIE 69. Those radiometers that performed best for the measurement of both small and extended sources of UVB and UVC had raised PTFE diffusers. We conclude that UV radiometers with a directional response error f2 < 10% are readily available commercially, and that it would be appropriate for future ultraviolet standards to set an upper limit of 5% on f2. This would ensure that the overall uncertainty in irradiance measurements of extended ultraviolet sources is not dominated by the error in the directional response of the radiometer.

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Spectral sensitivity of larval and juvenile coral reef fishes: implications for feeding in a variable light environment

Job¹,

Shand²

2001

Mar. Ecol. Prog. Ser.

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The spectral sensitivity of larval and juvenile stages of 3 species of coral reef fishes, Apogon compressus (Apogonidae), Pomacentrus amboinensis (Pomacentridae) and Premnas biaculeatus (Pomacentridae) has been investigated using feeding behaviour. Ontogenetic and taxonomic differences in spectral sensitivity were determined by establishing the minimum light intensity at which larvae and juveniles could strike prey at 12 restricted wavelength bands between 355 and 650 nm. Following construction of chromatic action spectra, the wavelength of maximum sensitivity (λ max ) and the median wavelength (λP 50 ) of the 3 species were found to be located close to 500 nm. All 3 species increased in sensitivity during growth, with A. compressus becoming the most sensitive prior to settlement. Ontogenetic shifts in spectral sensitivity towards longer wavelengths occurred in P. amboinensis and P. biaculeatus, but not in A. compressus. Spectral efficiency (wavelength-dependent efficiency of photon capture) was modelled for eutrophic and oligotrophic coral reef waters (Jerlov types Oceanic IA, Oceanic III and Coastal 1) at 2 different optical depths. Spectral efficiency was highest in the intermediate coral reef water type (JOIII) in all 3 larval fish taxa throughout early ontogeny, regardless of water depth. The results imply that the larvae would be able to feed across a broad spectrum of coral reef water types and depths.KEY WORDS: Colour vision · Chromatic action spectrum · Feeding behaviour · Ontogeny · Pomacentridae · Apogonidae Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 214: [267][268][269][270][271][272][273][274][275][276][277] 2001 to short wavelengths than closely related species from 'greener' eutrophic waters (Lythgoe et al. 1994). Similarly, the spectral positioning of double cones and the increasingly monochromatic short wavelength-shifted light environment of deeper waters appear to be correlated (Bowmaker et al. 1994).During the pelagic stage, larvae of coral reef fish may be transported by hydrographic processes across a range of water types (Williams et al. 1984, Doherty et al. 1995, Roberts 1997 and it is also known that there are depth-specific habitats for different larval taxa. For example, apogonids live at deeper depths than pomacentrids (Leis 1991a,b, 1993, Boehlert et al. 1992. Thus, both the spectral characteristics and light intensity of the ambient light environment the larvae of different taxa experience will differ from each other as well as from that of the reef-associated adults. However, nothing is known about inter-specific differences in the spectral sensitivity of coral reef fish during larval stages, and it is inappropriate to reconcile adaptations of adults to the variable conditions experienced by larvae (Warner 1997).Many marine teleosts hatch with a rudimentary visual system, with only 1 type of photoreceptor, and during the subsequent pelagic larval stage the structure of the eye undergoes rapid changes as the adult com...

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Basic Principles of Light Measurement

Cited by 3 publications

References 3 publications

Traceable calibration of ultraviolet meters used with broadband, extended sources

Traceable calibration of ultraviolet meters used with broadband, extended sources

A study of the directional response of ultraviolet radiometers: I. Practical evaluation and implications for ultraviolet measurement standards

Spectral sensitivity of larval and juvenile coral reef fishes: implications for feeding in a variable light environment

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