Luminous emission

A quartz window is set into the chamber and allows the luminous emissions to be detected by a photomultiplier fitted with a blue filter. 

Luminance is the luminous intensity divided by the area of emission of light (Iumens/steradian/m2). This is the power density emitted per unit area. 

The amount of light emitted by a source is measured by its luminance or by its luminous intensity, which are defined in Figure 18.2. Intrinsic light emission relates to the amount of light emitted per unit area (luminance). Table 18.1 lists approximate luminances for some common light sources. 

Fig. 9. Luminous efficiency vs peak emission wavelength for ( ) conventional commercial LED technologies. Also shown are data for the emerging...

Pig. 11. Luminous performance vs peak emission wavelength for the best reported high brightness LEDs. Some high performance lighting sources are indicated. The numbers in parentheses correspond to the source wattage. Also shown is the (—) eye response curve (as defined by the Commission... 

The current-voltage and luminance-voltage characteristics of a state of the art polymer LED [3] are shown in Figure 11-2. The luminance of this device is roughly 650 cd/m2 at 4 V and the luminous efficiency can reach 2 lm/W. This luminance is more than adequate for display purposes. For comparison, the luminance of the white display on a color cathode ray tube is about 500 cd/m2l5J. The luminous efficiency, 2 lm/W, is comparable to other emissive electronic display technologies [5], The device structure of this state of the art LED is similar to the first device although a modified polymer and different metallic contacts are used to improve the efficiency and stability of the diode. Reference [2] provides a review of the history of the development of polymer LEDs. 

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