Visible LED

A. T. Augousti, K. T. V. Grattan, and A. W. Palmer, Visible-LED pumped fiber-optic temperature sensor, IEEE Trans. Instrum. Meas. 57(3), 470-472 (1988). 

Most of the interest has been directed at making visible LEDs for which a Si H itself is not a candidate. Alloying with carbon increases the gap, and moves the luminescence into the visible region. The emission band is broad, and the room temperature emission is white at a carbon concentration of about 50 at%. 

It should be noted that the methods reviewed below can be applied not only to a planar substrate but also to convex and concave substrates. They can also be applied to an inner wall surface of a cylinder if it can be illuminated by propagating light. Furthermore, they can be used for a variety of materials, such as glasses, erystals, ceramics, metals, plastics, and so on. Since a high optical power is not required, visible LEDs can be employed as low-power-consumption light sources. 

Many types of semiconductor materials and devices have been developed to make infrared and visible LEDs. 

FIGURE 14 Evolution in performance of visible LEDs with time. 

The evolution in performance of visible LED materials with time is shown in Fig. 14 along with the performance of unfiltered incandescent lamps for comparison. Over the last 35 years LEDs have improved in performance to the point where the best LEDs have a higher luminous efficiency than tungsten incandescent lamps. 

A third alloy used for visible LEDs is (AlxGai jc)o.5 Ino.5P, which can be grown lattice-matched to GaAs substrates. The ratio of A1 to Ga can be changed without... 

A substantial fraction of visible LEDs produced today are the low-efficiency homojunction type. The efficiency... 

GaAsP GaAs or GaP GaAs (on GaAs substrates) GaP (on GaP substrates) GaAsP Visible LED s... 

In 2003, Chen et al. reported 363-nm ultraviolet LED using nonpolar a-plane AlGaN/GaN MQWs [25]. In 2004, Chitnis etol. reported visible LED using nonpolar a-plane InGaN/GaN MQWs [26]. Till 2004, there were no reports on optical power performance of nonpolar light emitters. The lack of low-defect density templates or substrates for the growth of LEDs was probably... 

Additional educational themes should include explanations of the mismatch that currently exists between speed limits and levels of protection, statanents of intent to improve road design and vehicle design over time, public scrutiny of vehicle advertising, and promotion of a new approach to managing offences, especially first low-level offences, with conunitment to the hypothecation of aU fine revenues to traffic safety purposes. The impact of education will be enhanced if all speed limit signs are active, that is, highly visible LED signs. 

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