Visual estimations of brightness and use of ordinary photometric or colorimetric light meters are inappropriate. 2 Clinical Contextįor routine measurements, clinicians are limited by reliance on irradiance meters supplied or recommended by the manufacturer. Consequently, different radiometers may show different values for the same light source. In addition, the calibration methods, wavelength responses, and geometries of instruments are not standardized. Currently, no single method is in general use for measuring phototherapy dosages. ![]() nm −1) might have (as-yet-unidentified) adverse effects.1 Devices that emit lower irradiance may be supplemented with auxiliary devices. nm −1 over the waveband interval 460 to 490 nm.15, 16 The American Academy of Pediatrics has recommended that the irradiance for intensive phototherapy be at least 30 μW A direct relationship between irradiance and the rate of in vivo total bilirubin concentration decrease was described in the report of a study of term “healthy” infants with nonhemolytic hyperbilirubinemia (peak values: 15–18 mg/dL) using fluorescent Philips daylight (TL20W/54, TL20W/52) and special blue (TLAK 40W/03) lamps. Often, radiometers measure wavelengths that do not penetrate skin well or that are far from optimal for phototherapy and, therefore, may be of little value for predicting the clinical efficacy of phototherapy units. Table 2 compares the spectral irradiance of some of the devices in the US market, as measured with different brands of meters. 1 Irradiance is measured with a radiometer (W Determination of an in vivo dose-response relationship is confounded by the optical properties of skin and the rates of bilirubin production and elimination. 1 The dose of phototherapy is a measure of the irradiance delivered for a specific duration and adjusted to the exposed body surface area. Light intensity or energy output is defined by irradiance and refers to the number of photons (spectral energy) that are delivered per unit area (cm 2) of exposed skin. 9, –, 14 Unless specified otherwise, plastic covers or optical filters need to be used to remove potentially harmful ultraviolet light. 8, 9 Most recently, commercial compact fluorescent-tube light sources and devices that use LEDs of narrow spectral bandwidth have been used. 6, 7 More effective narrow-band special blue bulbs (F20T12/BB or TL52/20W ) were subsequently used. ![]() 2 The first prototype phototherapy device to result in a clinically significant rate of bilirubin decrease used a blue (B) fluorescent-tube light source with 420- to 480-nm emission. 2, 4, 5 Because of the photophysical properties of skin, the most effective light in vivo is probably in the blue-to-green region (∼460–490 nm). Absorption of light transforms unconjugated bilirubin molecules bound to human serum albumin in solution into bilirubin photoproducts (predominantly isomers of bilirubin). ![]() Bilirubin absorbs visible light most strongly in the blue region of the spectrum (∼460 nm). The visible white light spectrum ranges from approximately 350 to 800 nm.
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