Philips LED Lighting
Philips LED Light Bulbs
I recently replaced half of the light bulbs in my house with Philips LED
lighting. Compared to the prior CFL bulbs, LED bulbs offer the
|Even color spectrum
||The LED bulbs produce much nicer looking light than the CFLs. The
LEDs better approximate the color spectrum of incandescent
|Low power consumption
||The LED bulb consumes 8.5 watts whereas the CFL bulb consumes 14
watts. Both produce 800 lumens.
|Full brightness at start-up
||LEDs do not share the CFL's problem of being dim when cold.
The Philips LED bulbs cost less than $2 each at the big home improvement
stores. The cost is undoubtedly being subsidized by the local electric
company. At that price, there is no reason to buy any other kind of
Curious what went into a $2 bulb, I drew the schematic from the photos
of the circuit board available on the Internet. Since only a portion of
the traces were visible, I filled in the missing traces.
LED Light Bulb Schematic
The circuit is a conventional buck converter that supplies constant
current to the LEDs. A key feature is temperature regulation: the
regulator reduces the LED current when the bulb's internal temperature
reaches a preset limit.
The use of temperature regulation enables the bulb to be designed
without the usual overprovisioning of the cooling system needed in
electronic equipment that must operate over an ambient temperature range
of 0-35C. Instead, the bulb can be designed to operate at its thermal
limit under any external conditions. This is key to reducing cost.
In the 1970s, I wondered when the then-new LEDs would be used in
household lighting. Nearly half a century of technological progress has
made this a reality. The main enablers were the invention of white LEDs
(which are really blue LEDs with a phosphor), and surface-mounted
electronic components (to make a switching power supply fit in the base
of a light bulb).