Читать книгу Patty's Industrial Hygiene, Physical and Biological Agents - Группа авторов - Страница 122

Portable, easy‐to‐use broadband detectors for optical radiation are widely available. Electronic broadband detectors for UV, visible, and IR‐A radiation typically use a semiconductor photodiode that produces a current proportional to the photon flux at a given wavelength. The spectral responsivity of a photodiode may be defined as the ratio of current generated to radiant power incident on the detector. Based on Eqs. (1) and (2), the incident power is proportional to the photon flux and inversely proportional to the wavelength. The spectral responsivity also depends on the inherent quantum efficiency of the device, which is a function of λ, and on the spectral transmittance of any filters and input optics. Some UV detectors include a phosphor that absorbs UV and emits visible photons that are detected by the photodiode.

Detectors are commercially available with relative spectral responses that approximate the ACGIH relative spectral effectiveness function S(λ) for UV, the CIE erythema reference action spectrum S_er(λ), the ACGIH blue‐light hazard function B(λ), and the ACGIH retinal thermal hazard function R(λ). Photometers, which are used to measure illumination levels, have a spectral response matched to the photopic luminous efficiency function. Unweighted IR irradiance may be measured using thermopile or pyroelectric detectors, which give a nearly uniform response over a wide spectral range.

Performance characteristics for broadband UV radiometers have been described by the World Meteorological Organization for measurement of solar erythemal radiation (23) and by the CIE 220:2016 guideline for measurement of artificial sources (27). Radiometers with broadband detectors are typically calibrated to read out directly in irradiance units such as W m⁻². Integrating radiometers can be set to measure radiant exposure received over time. An evaluation of the directional response of broadband UV detectors from seven different manufacturers with four different main types of input optic found that raised polytetrafluoroethylene (PTFE) dome diffusers showed the best directional response compared to recessed PTFE diffusers, quartz diffusers, or no diffuser (28). The raised PTFE diffusers had directional errors of 4–10% relative to an ideal cosine response. Modeling suggests that optimized raised planar diffusers and dome diffusers can have directional errors less than 2% (29), and some commercially available diffusers are reported to have directional error in this range. UV sources that subtend an angle greater than 80° need only be measured over a field of view of 80° (15). For assessments of retinal hazards, measurements of source radiance should be made using a detector equipped with input optics that narrow the field of view to 0.011 rad (30).

Personal UV dosimetry methods used in research on occupational or community UV exposure include small electronic dosimeters, UV‐sensitive chemical films such as polysulphone (34) and poly(2,6‐dimethyl‐1,4‐phenylene oxide) (PPO) (35), and UV‐sensitive biofilms (36, 37). A wearable sensor patch has recently been developed that uses UV‐induced color change in a dye, which is read using a smartphone app, to measure personal erythemal dose (38). Electronic personal dosimeters or dataloggers with spectral response approximating the CIE erythemal or ACGIH/ICNIRP UV‐hazard functions are commercially available.