Five A19 base dimmable LED bulbs with warm light output equivalent to a 60 watt incandescent bulb have been tested and reverse engineered. While all the bulbs show good performance some significant differences have been identified. Full circuit details of each bulb are found on separate pages. Physical and performance characteristics of the LED bulbs are summarized below:
Physically the bulbs are all quite similar, having a power conversion circuit board located within the A19 base connected to a separate board with the LEDs located within a plastic globe. All the bulbs except the Philips product have LEDs mounted on an upward facing aluminum disk. The Philips bulb has LEDs mounted on a pentagonal cross section heat sink to direct light in 6 directions. All of the products have a plastic base with an aluminum insert to draw heat away from the LEDs. The base of the Cree bulb is filled with potting compound which provides additional heat conduction.
From a circuit point of view all 5 of the bulbs employ a non-isolated buck-boost converter. The Philips and GE bulbs use discrete transistor circuits while the other 3 bulbs employ integrated circuit power conversion controllers. The Cree and EcoSmart bulbs require an external power MOSFET to limit the voltage seen by the controller IC, while Sylvania bulb needs no additional transistors. All the bulbs use a full wave rectified AC input voltage to power the switching converter which produces a DC voltage for the LED strings. The Philips circuit shown on the right has the highest component count totaling 84 which includes 26 LEDs. The Sylvania bulb in the middle has the lowest component count at 37 including 16 LEDs. The EcoSmart bulb has only 9 LEDs, the lowest number among the bulbs tested.
The Philips and Cree bulbs are more expensive and have the longest rated lifetime of 22.8 years at 3 hours use/day, corresponding to 25,000 hours. The other 3 bulbs are rated at 13.7 years at 3 hours use/day, corresponding to 15,000 hours. The extended life and cost of the Philips and Cree products may be due to additional efforts to cool the bulb. Philips has a 3-dimensional LED mounting structure while Cree is filled with potting compound. During full power operation the Cree and Philips bulbs showed a temperature of 65 degrees at the narrow portion of the base. In contrast the other 3 bulbs had temperatures ranging from 70 to 72 degrees. The base of the incandescent bulb at full power was only 53 degrees as most heat is radiated directly from the bulb whereas most heat in the LED bulbs is concentrated in the base.
LED bulbs have been available for some time, but now in 2017 we see the non-isolated buck-boost converter well established as the dominant design among the major brand names. The advantages over incandescent bulbs are clear but will consumers appreciate the more minor differences among different LED products, such as light distribution, lifetime, or 20% differences in efficiency? Will the integrated circuit controller win over discrete transistor solutions? Only time will tell.....
2017.08.21
The following graph shows the light distribution from the 5 LED bulbs and a 60W incandescent bulb at full power. 0 degrees is the top of the bulb and 180 degrees is the base of the bulb where the light is completely blocked. Most of the LED bulbs have a fairly uniform distribution from +90 to -90 degrees. The Philips bulb has a more compressed light distribution with more light at the sides than the top, similar in character to the incandescent bulb.
All the bulbs perform well with a triac dimmer as advertised. The Sylvania product provides the highest light output but all 5 LED bulbs greatly exceed the light output of the 60w incandescent bulb. None of the measurements show the rated light output of 800 to 815 lumens. A calibration error in the measurement equipment is suspected but the relative results are valid. The Philips bulb shows a significant drop in light output from 75% to 50% power as the "warm glow" feature is activated. In contrast to the linear characteristic of the LED bulbs, the incandescent bulb light output declines exponentially with reductions in dimmer setting.
The Sylvania bulb is the most efficient in converting electrical power to optical power, achieving 10.7% at the maximum dimmer setting. The efficiencies of the Philips and EcoSmart bulbs drop off significantly at the lowest dimmer setting. As expected, the LED bulbs outperform the incandescent bulb in every way.
