Photopic response

In human eye units, watt becomes lumen. At 555 nm, the peak sensitivity of the photopic response, there are 683 lm/W. A watt is a joule per second, and a photon has energy in units of joules. A watt tells us how many photons per second are coming out of the OLED. A lumen... 

Radiant intensity can be described as the amount of power (watt) heading in your direction, i.e., per steradian, from a light source. The total amount of power emitted by the source is the radiant flux (watt). If you integrate the radiant intensity over all solid angles, you get the total radiant flux. If it is weighted by the photopic response, then it is the luminous intensity and the luminous flux. 

Figure 1 Photopic response of the human eye. Source Courtesy of the Newport Corporation.

The conversion of radiated power (F in watts) to luminous flux (F in lumens) is achieved by considering the variation with wavelength of the human eye s photopic response. Then the spectral power from the source (P in, for example, W/nm) is convoluted with the relative spectral response of the eye (V tabulated by the CIE) according to ... 

The luminous efficiency, T7l, in cdA is convenient for quantifying the properties of an OLED for display applications. In many respects, T7l is equivalent to 77ext> with the exception that tjl weights all incident photons according to the photopic response of the eye. While Tjext weights all photons equally, if emitted in the invisible spectral regions they would not contribute to rji. A problem arises, however, when these photometric efficiencies are... 

In the case of dichroic (especially monochrome) displays, the contrast ratio is sometimes measured at A ,ax which shows the maximum capability of the dye but does not correspond to the photopic response. The contrast ratios calculated using the radio-metric equipment (or in arbitrary units of radiance) also differ from those evaluated using photometric equipment. Bloom and Priestly [94] therefore defined the perceived contrast ratio (PCR) ... 

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