LED Bulb Design Challenges
Unlike the Edison incandescent bulb that just uses AC-line power, LED bulbs fundamentally require a constant DC-current to be drawn through the LEDs to produce light. Along with such AC-DC conversion in the bulb, there is additional circuitry to insure safety, noise compliance, regulation and smoothness of operation. Furthermore, the LEDs themselves are like integrated chips, requiring careful management of heat to ensure reliability and performance over time. And hence the start of wide variety of complications and trade-offs required in the design.
Although LED bulb prices have come down significantly from the $25-$30 USD range just a few years ago, they are still above the threshold considered to drive rapid mass adoption. Quicker gains in manufacturing and volume ramps have already been made, and the next factor-of-two reduction in price requires another round of innovation to reduce the Bill-of-Materials (BOM) cost. This is a fundamental challenge facing the LED bulb OEMs and the industry at large. Because the LED driver chip itself is the heart of the power supply for the LED bulb, choice of the LED driver architecture, features and required external components have significant impact on the cost of the full solution.
Heat management is a very critical factor with LEDs to ensure desired reliability and performance. Although dissipating only a small fraction of the heat radiated by an incandescent bulb, the LED bulb still requires a heat-sink and very careful thermal design to ensure reliability of the LEDs and long product lifetimes. Maximizing efficiency of the LED driver circuits, therefore, is critical for performance, cost and reliability of the designs. Every bit of efficiency improvement delivered by the LED driver IC ripples through – enabling lower product cost and higher reliability.
Dimmability / Compatibility
One of the attributes of incandescent bulbs expected and taken for granted by consumers is that they are all readily dimmable with existing dimmers, and over their full 100-0% range, without functional or quality issues (deep dimming). Consumers expect Universal Dimmer Compatibility when they screw in the incandescent bulbs into these sockets, and do not expect to read through fine print concerning limited dimmer compatibility, and/or the need to change expensive pre-existing dimmers just to swap in the new LED bulbs.
Quality/User Experience of Light
Light is an extraordinarily potent driver in how we experience our environment. It drives our mood, and communicates more directly with us than any of our other senses. LEDs have significant advantage over the CFL lights in their ability to produce a full temperature range of colors, and with high-color rendering index (CRI) – affording better color quality experience to the users. Despite dramatic improvements in color quality, however, most current generations of LED bulb products can and do still grossly misbehave in the presence of dimmers and energy management sensors, with issues like non-monotonic output, very limited dimming range, visible flicker, strobing, and/or being stuck on or off. Almost needless to say, the color quality of the light becomes quite irrelevant when the light itself is flashing or otherwise misbehaving.
Reliability – Consumables vs. Durables
Typically consumers have treated bulb purchases as a consumable choice – bought at commodity prices and replaced as needed. Now the industry is asking for shift in consumer behavior to think of LED bulbs as durables. DOE studies identified “Unpredictable Lamp Life” of early generations of CFLs as one of the top reasons of poor consumer experience with CFLs – a dampening and finally a limiting factor in final adoption of CFLs. An LED bulb is as reliable as the weakest component inside it, and often these are not the LEDs, but other internal components in the LED driver circuits. LED driver designs must innovate on reducing component count and utilizing type of components essential for higher reliability at lower cost; thereby delivering high user satisfaction expected of a durables purchase.
For LED bulbs to be the product of consumer choice to replace the 130 year old incandescent bulbs in 3.3 billion Edison screw sockets in the US – and many more billions worldwide – the OEMs must very rapidly and effectively address all of the above issues in LED light designs.