Luminous sensitivity

Comparison of the luminous sensitivities of the image dissector and the silicon target vidicon Image Dissector Silicon Target Vidicon... 

The data in Tables VII and VIII suggest that for emission measurements, the detection limits for the image dissector are lower than those for the silicon vidicon by a factor of about 24. The decrgase in the detection limit ratio at longer wavelengths (> uSOOOA) results from a decrease in the luminous sensitivity of the image dissector relative to the silicon vidicon. The effect is quite apparent in the case of potassium. 

Several different definitions are used to speeify the effieieney of a PMT eathode. Often the sensitivity of a PMT is speeified in units of eathode luminous sensitivity". This is the cathode eurrent per lumen incident light from a tungsten lamp operated at a temperature of 2,856 K. Beeause the intensity maximum of the lamp is at about 1,000 nm, the luminous sensitivity may not represent the efficiency at a given wavelength. Photocathodes of different spectral sensitivity are therefore not directly comparable. Moreover, the cathode luminous sensitivity does not include the effieieney of the eleetron transfer from the cathode into the dynode system and the possible loss of photon pulses due to incomplete resolution of the pulse height distribution (see Fig. 6.27, page 241). 

In the test sheets of PMTs, the manufacturers occasionally specify the measured anode luminous sensitivity" instead of the cathode sensitivity. The anode sensitivity is the cathode sensitivity (including the electron transfer efficiency) multiplied by the gain of the tube. Because almost any gain can be obtained by increasing the supply voltage, the anode luminous sensitivity cannot be used to compare the photon counting performance of PMTs. 

Fig. 6.27 Measurement of the Cathode Luminous Sensitivity (Ze/f) and the Anode Luminous Sensitivity (right)...

The Anode Luminous Sensitivity" is measured in a similar setup as the Cathode Luminous Sensitivity. However, the PMT is operated in the normal way, i.e. by applying the specified voltage distribution to the dynode chain (Fig. 6.27, right). Of course, a calibrated filter has to be inserted in the light path to attenuate the light of the lamp to a level that does not overload the PMT. As mentioned before, the anode luminous sensitivity is not very useful in characterising a PMT for TCSPC. 

The eathode luminous sensitivity" is the eathode current per watt incident light power from a tungsten lamp operated at 2,856 °C. The cathode luminous sensitivity is the integral of the product of the eathode radiant sensitivity and the lamp speetrum. Beeause the lamp has its emission peak in the NIR the cathode luminous sensitivity lets the sensitivity of NIR-sensitive cathodes appear higher than it aetually is. 

Luminous lu-m9-n9s adj [ME, fr. L luninosus, fi-. lumin-, lumen] (15c) (1) Adjective used to imply dependence on the spectral response characteristic of the Standard Observer defined in the CIE System. Thus, the luminous reflectance or the luminous transmittance is described by the Y tristimulus value in the CIE System. The adjective is applied to many measures of light, such as intensity, density, etc., and always indicates the measures are weighted for the relative luminous sensitivity of the human observer. (2) Material emitting or spearing to be emitting, visible radiant energy. 

Contrast C is the contrast of the luminances between the object Lo and its surroundings Ls C = (Lo - Ls)/Ls. With increasing contrast, visibility increases Adaptation luminance L,d, is the luminance to which the eye adapts its sensitivity. It corresponds to the luminance of the field of vision. With increasing adaptation luminance, visibility increases. 

Eor LEDs utilized in visible/display appHcations, the human eye serves as the detector of radiation. Thus a key measure of performance is luminous efficiency which is weighted to the eye sensitivity (CIE) curve. The relative eye sensitivity, V (L), peaks in the green at A 555 nm where it possesses a value of 1.0. It drops sharply as the wavelength is shifted to the red or blue, reaching a value of 0.5 at 510 and 610 nm. The luminous efficiency, in units of Im/W, of an LED is given by equaton 11 ... 

While barbiturate metabolites are more intensely colored by the mercury(I) nitrate reagent (q.v.) the unaltered barbiturates react more sensitively to the mercury(II) diphenylcarbazone reagent the detection limits lie between 0.05 pg (Luminal ) and 10 pg (Prominal ) per chromatogram zone [6]. 

The interaction of IP3 with its receptor involves complex and poorly understood regulatory interactions among the receptor, IP3 and Ca2+ - the latter apparently exerting influence from both the cytoplasmic and luminal aspects of the receptor. Ca2+ in the lumen of the ER appears to sensitize the receptor to IP3. On the cytoplasmic surface, low concentrations of Ca2+ sensitize while higher concentrations are inhibitory. These actions may contribute to the all-or-none oscillatory behavior of [Ca2+] signals seen in some cell types. This phenomenon will be discussed in more detail below. 

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