What Are LED Lamps?

Dynamic Lighting Frequency

LEDs are compound semiconductor devices. Their optical wavelength depends on the elements and the ratio between them. An LEDs luminescence is based on the recombination of the minority carriers (holes and electrons) in a PN junction. Table 1 shows typical LEDs materials and their emitted wavelengths. (Series Name refers to our Toshiba Line of LEDs).

Figure 1 shows the basic structure of an InGaAlP LEDs chip. From top to bottom, the figure shows the P-electrode, the P-side current diffusion layer, the emission layer between clad layers, the N-side layer substrate, and the N-electrode. Current flows from the P-electrode to the N-electrode. That is, current flows from the P-electrode (the bonding post) to the P-side current diffusion layer, which diffuses the current.

The current then flows to the emission layer and out to the N electrode.

Figure 2 shows the structure of an LEDs chip with a current blocker as recently adopted for high-brightness LEDs. In the basic structure shown in Figure 1, most of the light emission directly under the P-electrode is in the shadow of the P- electrode and is therefore not emitted externally. Hence, the current used for this shadow area is wasted. Toshiba overcomes this by inserting a current-blocking layer directly under the electrode to block any current that would otherwise be lost under the electrode. Figure 2 shows the structure an LEDs chip in which the current flows only to the parts that will emit light externally.

Toshiba uses this structure in its high-brightness LEDs, such as the TLxH series. Toshiba also offers LEDs chips with other types of structure.

LED Lamp Structure

Figure 3 compares lead-type (conventional type) LEDs lamps and SMD (surface-mount device) LEDs lamps.

Recently, SMD LEDs have become very popular and are now found in a variety of devices, notably in various kind of portable equipment. The main feature of SMD LEDs is their potential for device miniaturization.

Figure 1 - Example of double hetro junction LED structure


Figure 2 - Example of structure of LED with current blocking layer


Figure 3 - Typical LED lamp structure

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