Bench Talk

I have a smartphone. You have a smartphone. We all have smartphones. With that, we have become a world with a camera always on hand.

I confess that before the arrival of smartphones, I never carried around a camera no matter the significance of the event. While dating my wife, while on vacation (I’ve seen some amazing places that I can still picture), or while my children were playing: No camera. The reason? I never wanted to be bothered with all the work associated with carrying a camera around, only to obtain abysmal results of shooting fuzzy pictures and creating red eyes that make people look like wolves.

Well, with the introduction of the smartphone that all changed. Suddenly the camera is always with me, and it takes excellent pictures. Just aim, hit the screen to focus, and—Voila!—great pictures. Estimates predict that more than one trillion digital photos will be taken this year using a smartphone. Just like auto-focus capabilities have made smartphones an easy-to-use camera with good results, I want to make something stress-free for you: understanding the differences between mid-power LEDs and high-power LEDs.

Most of us know that LED is an acronym for Light Emitting Diode. LEDs have become ubiquitous and are used in a variety of applications, because they’re small, energy efficient (in lm/W), robust, reliable, and feature-full. The main difference between these two categories is apparent from their name: mid-power and high-power. However, to be complete, we must add a third category: Low-Power. Now, we have three classifications of power for LEDs.

As electronic engineers, we know from Ohm’s Law that Power (W) = Voltage (V_DC) × Current (A), or mathematically stated, P = E × I. So, let’s look and see how these three power levels (low, mid, and high) are categorized (Table 1).

Table 1: Rough characterization of low-, mid-, and high-power LEDs levels in watts.

The first thing to be aware of is there is no written international standard defining these categories. The classifications are instead an internal development that has happened as a naming nomenclature within the industry, which arose over time: Low-power, High-power, and Mid-power.

Low-Power

The initial LEDs that were developed and employed in consumer applications were low-power. They often function as indicator lights, identifying the status of some condition.

High-Power

Due to their high cost, high-power LEDs were initially used mainly within the research and development of applications domain. In the past decade or so, tremendous gains have been made in manufacturing techniques and processes that allow much higher levels of current to be applied to the semiconductor junction itself, making for explosive growth in the area of high-power LEDs. Commercialization of high-power white LEDs has led to their introduction and ongoing takeover within illumination applications that were traditionally occupied by incandescent and halogen technologies.

Mid-Power

Over time, LED manufacturers recognized an unfilled niche: Applications calling for white light delivered in linear packages. These applications were best served by developing products that could deliver high efficacy, while overcoming illumination uniformity concerns and thermal overloading of the mounting infrastructure. Responding to these needs, LED manufactures introduced a variety of mid-power LEDs that now occupy the highest market share position within general illumination applications. The diodes in these LEDs are packed more densely, relative to high-power white LEDs, and give a more uniform appearance. Their lower power consumption often allows standard PCB materials, such as FR-4 printed circuit boards, to be used (as opposed to more expensive, heat-sinking alternatives, such as metal-core PCBs and the like). Mid-power LEDs find their application niche most often within general illumination applications, where size and uniformity take precedence over raw, optical output power. Indoor area lighting is a common use, including A19, ceiling, task, downlights, and both low and high bay applications.

LED manufacturers, including Cree, Lumileds, and OSRAM Opto Semiconductors, are all significantly investing in mid-power LEDs. In April of this year, Cree announced a joint venture to market a broad portfolio of high-performance mid-power products, to serve the fast-growing, $4 billion global mid-power LED market. Cree sees this as an opportunity to serve the broader needs of the general illumination (indoor and outdoor lighting), horticultural lighting, and other evolving LED markets. Lumileds LUXEON SunPlus 2835 LEDs are mid-power devices offering perfected performance, built on a proven legacy (Figure 1). The OSRAM Opto Semiconductors OSCONIQ P2226 LED series comes in various colors, including deep blue (450nm), blue (465nm), true green (525nm), yellow (595nm), red (623nm), and far-red (730nm), allowing designers to have the color flexibility to accommodate a large variety of applications.

Figure 1: LUXEON 2835 Line is a collection of compact devices that allows for design freedom and provides a superior overall system solution when a project requires high lumen output and good efficacy. (Source: Lumileds)

Picture this. Mid-power LEDs are now frequently used as Flash LEDs, to take digital pictures, and find themselves commonly designed into the smartphones we use. So mid-power LEDs are helping to make my life a whole lot easier, and yours too! Now, if only I could flash back to yesteryear!