For wavelengths ranging from 390 to 720 nm, the eye sensitivity function V(X) is greater than 10-3. Although the human eye is sensitive to light with wavelengths < 390 nm and > 720 nm, the sensitivity at these wavelengths is extremely low. Therefore, the wavelength range 390 nm < X < 720 nm can be […]

The conversion between radiometric and photometric units is provided by the luminous efficiency function or eye sensitivity function, V(k). In 1924, the CIE introduced the photopic eye sensitivity function V(k) for point-like light sources where the viewer angle is 2° (CIE, 1931). This function is referred to as the CIE 1931 V(X) function. It is […]

The physical properties of electromagnetic radiation are characterized by radiometric units. Using radiometric units, we can characterize light in terms of physical quantities; for example, the number of photons, photon energy, and optical power (in the lighting community frequently called the radiant flux). However, the radiometric units are irrelevant when it comes to light perception […]

Figure 16.1 (a) shows a schematic illustration of the human eye (Encyclopedia Britannica, 1994). The inside of the eyeball is clad by the retina, which is the light-sensitive part of the eye. The illustration also shows the fovea, a cone-rich central region of the retina which affords the high acuteness of central vision. Figure 16.1 […]

The recipient of the light emitted by most visible-spectrum LEDs is the human eye. In this chapter, the characteristics of human vision and of the human eye and are summarized, in particular as these characteristics relate to human eye sensitivity and photometric quantities.

A complete discussion of other light-emitting structures that confine photons is beyond the scope of this chapter. It is useful, however, to discuss the properties of some confined-photon emitters. Photonic crystal or photonic bandgap structures or involve two — or three-dimensional photon confinement achieved by periodic patterning of the light-emitting active region or the material […]

RCLEDs have also been demonstrated in the visible wavelength range using the AlGaInP material system (Streubel et al., 1998; Whitaker, 1999; Wirth et al., 2001, 2002). The AlGaInP material system is commonly used for high-brightness red, orange, and yellow emitters and can be grown lattice matched on GaAs substrates. The active region of RCLEDs is […]

The structure of an RCLED with a GalnAs active region is shown in Fig. 15.4 (a). The cavity is defined by one distributed Bragg reflector (DBR) and one metallic reflector. Also included are two confinement regions and a four-quantum-well active region. The heavily doped n-type substrate is coated with a ZrO2 anti-reflection layer (Schubert et […]

The basic structure of an RCLED is shown in Fig. 15.1 and comprises two mirrors with reflectivity R1 and R2. The reflectivity of the two mirrors is chosen to be unequal so that the lightexits the cavity predominantly through one of the mirrors. This mirror is called the light-exit mirror. Here we designate the mirror […]

The resonant-cavity light-emitting diode (RCLED) is a light-emitting diode that has a light — emitting region inside an optical cavity. The optical cavity has a thickness of typically one-half or one times the wavelength of the light emitted by the LED, i. e. a fraction of a micrometer for devices emitting in the visible or […]