The modern white LED tends to generate a significant amount of heat, and always require special attention to thermal management during custom LED lighting designs. Due to thermal issues, a special slug integrated into modern white LED packages helps to transfer heat away from the junction to an external heat sink. Older, traditional light emitting diodes, such as the 5mm LED, produce less heat, and do not require the special slug. The wire-leads or pads will still help with heat dissipation, but are not nearly as efficient as a modern white LED with integrated slug. Most traditional white 5mm LED lights are physically smaller and operate at reduced drive currents.
Although traditional 5mm LED lights are less efficient, they serve a purpose in many special designs. Newer high-powered white LEDs require special attention to thermal and power management. In addition, most high power white LED lamps feature a wide beam angle, as great as 180 degree in some cases. The light emitting diode requires the addition of a secondary optic if the lighting application requires a narrow beam angle, such as 20 degrees. When space is limited, the secondary optic is not always feasible. The traditional 5mm LED tends to feature a much narrower beam angle, usually between 10 to 50 degrees. Since a secondary optic is not required, the traditional light emitting diode would be more suitable for such an application. The traditional 5mm LED does not only feature a narrower beam, but also require fewer external components to operate. This can provide further cost savings in elementary custom lighting designs. Yet another advantage of the 5mm LED includes overall optical wavelength diversity. For example, it may be somewhat difficult to find a high power white LED with an optical wavelength rated at 420 nm or 660 nm. However, the 420 nm purple and 660 nm red are readily available as a traditional 5mm LED.
Selecting the most appropriate light emitting diode for an application often comes down to the total amount of light availability and costs. Many manufactures base their price structure on the idea of lumens per dollar. As rival companies compete for business, sales and marketing personal boast about the cost efficiency of their products. It is true that leading competitors can offer spectacular deals as far as cost efficiency based on the lumens per dollar formula. However, numerous applications require special considerations with precedence over cost efficiency. Consider an application that requires an extremely narrow beam angle such as 15 degrees. A traditional 5mm LED device would most likely meet this critical requirement, but may only offer six lumens per dollar. The competition may offer a high power white LED device providing an amazing twenty lumens per dollar. Although this is very attractive to the buyer, in this case, the 5mm LED device is more appropriate even though it lacks in the area of cost efficiency. Some manufactures claim that external optics designed especially for their light emitting diodes can achieve narrow beam angles when required. Although this is true, it requires additional space and reduces cost efficiency. A high power device offering twenty lumens per dollar might end up providing only ten lumens per dollar after factoring for material and assembly costs associated with an external optic. Other common examples where traditional 5mm LEDs are most suitable include applications where physical package size, heat dissipation, and drive current restrictions restrict the use of modern high power LED devices. In conclusion, modern LEDs offer numerous technological advantages, but traditional LEDs are still more appropriate in some special applications.
Surface mount LED technology (SMT) has grown in popularity due to design advantages and reduced assembly costs. Applications such as cell phones and laptop computers commonly utilize traditional surface mount LED lights. Their low profile package design is extremely beneficial in applications where space is limited. The white surface mount LED is physically smaller in most cases, when compared with the previously discussed 5mm LED through-hole part. Two primary case styles include the flat and domed lens package. Domed lens packages are less common, but tend to offer a narrower beam angle due to the spectral properties of the lens. Surface mount LED availability is vast and continues to grow as the demand for surface mount technologies increases. However, LED manufactures are not producing SMT devices with narrow beam angles, ideal in some applications. A surface mount LED with a 20 or 30-degree beam angle is extremely rare. Instead, most devices contain a 100 to 150-degree beam angle.
The traditional 5mm LED is perhaps the most famous and widely used LED lamp today. The device features a cylindrical body with a domed lens. Two wire-leads, the anode and cathode, protrude from the bottom of the transparent case. Most 5mm LEDs feature a narrow beam angle between 10 degrees and 50 degrees. Color availability is extremely diverse. Most 5mm LEDs are 100 mW devices. They typically operate at 20 mA and drop 3.0 to 3.6 volts across the junction. Popular drive circuitry includes pulse width modulation as well as resistor driven circuits. Forward voltage drops are relatively stable permitting the use of resistors in simple but cost efficient resistor driven circuits. Almost all light emitting diode manufactures have included the traditional 5mm LED in their product lines.