'Green' energy emerging from two lighting systems
Posted: 09 Oct 2008
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Despite the attention drawn on other sources of energy to increase available power, some measures are targeted to the conservation of energy. Along with "making more," the energy challenge is also aimed at "using less."
Hybrid vehicles have gotten much attention in the car industry's conservation effort and automobiles are a major part of the energy puzzle. Home and commercial lightings have also shown significant usage, accounting from 15 percent to 35 percent of all their energy consumption. The workhorse incandescent lamps that came many years ago remain widely used, but they have abysmal efficiencies of generally below 5 percent and have spurred changes.
Two technologies are emerging and likely to grow as pressure mounts to lower electricity use such as the compact fluorescent lamp (CFL) and LED lamp. Both are moving toward, if not being legislated into, more applications in the search for conservation.
One of these two technologies has been on a steady march for affordability, and Planet Analog editor Bill Schweber recently sent me a pile of CFLs, now available as sub-$5 replacements for incandescent bulbs, as a not-so-subtle recommendation for a teardown. But CFL is not alone and Bill's hardware handout made me think of the other contenders in the game. LED lighting has made contributions, but steady progress as a viable replacement for the inefficient incandescent, and a high-brightness LED "downlight" recently released to the market caught my eye.
Fluorescent vs. incandescent
The fluorescent bulb is substantially more efficient than the incandescent option, producing greater direct light and less heat per input watt. Although they have long been used in offices and other commercial and residential settings, fluorescent lamps didn't come in forms suitable for small-lamp substitute until the 1980s. The last two decades have seen miniaturized screw-in CFL bulbs that finally achieved quite low-price points, promoting consumer adoption.
The MaxLite bulb examined is a 20W lamp believed to produce equivalent illumination to a 75W incandescent. Like all of its other fluorescent peers, the MaxLite CFL uses a glass tube whose phosphor lining emits from UV radiation created by ionized gas in the tube. The CFLs have miniaturization through both a smaller tube diameter and through folded or spiral-wound construction. The CFL ballast used to light the tube also must be stuffed into the space constraints of a standard screw-in lamp. To do this, the MaxLite and its competitors use a downsized supply to develop a suitable lamp drive in relatively less space.
A pair of transistors, quartet of diodes and collection of capacitors and inductors—all come together to first rectify the AC power and make a follower resonant inverter circuit that creates the high-frequency, high-voltage power used to fire the lamp. I'm no power supply expert so I may have the precise topology wrong, but both inspection of the minimal components and finished goods' price points show that the CFL ballast can be made inexpensively.
The phosphor-coated glass tube has its own history in manufacturing such that the combination of lamp and electronic drive circuits can now be brought to market at prices that start to rival the relatively short-lived incandescent alternative. When efficiencies and lifetimes are considered, the CFL begins to look attractive not only for its "green" attributes, but also for total cost of ownership.
Wear out of lamp phosphors remains an issue, and vent holes in the lamp-base enclosure suggest that heat-related wear out of ballast electronics might be a factor. Still, the lifetime of quality CFLs can run to many months or even years.
The advancement of LED
The LED has shown its own transformation. No longer relegated to red, orange, yellow, green or blue, the white LED brings more livable light into the mix. White LEDs (WLEDs) are actually blue LEDs coated like the CFL tube with a phosphor stimulated into emission by the internal LED's blue light. WLEDs are the staple for small LCD backlight and the rise of high-brightness WLEDs is now moving the technology into the realm of both larger LCD backlighting and general illumination.
Cree Lighting Co. has been an innovator in SiC-based blue LEDs central to the WLED construction, and in February, the company bought LED Lighting Fixtures (LLF), in an attempt to capture more of the value chain around its high-brightness devices.
The specific product acquired for this column, Cree/LLF's LR6 can "downlight," was acquired at a local lighting contractors' store for a sum of $100, plus tax. The price reflects the limited nature of high-brightness LED production against CFL. Simply, a mix of technology lock-ups and the more expensive production needed for the WLEDs means not everyone can pile on, but yet to drive costs down.
The LR6 produces a claimed lumen output equivalent to a 65W incandescent lamp with a more miserly 12W of input use, making it 80 percent more efficient than the incumbent tungsten-filament bulb and roughly 50 percent better than the CFL.
Construction of the light is driven partly by the retrofit nature of the LR6, which is meant to screw directly into a traditional can light's lamp base. However, the housing is a substantial cast-aluminum, finned structure. This adds significantly to the costs and seemed like overkill in light of the minimal 12W draw. I must be missing something there.
Viable circuitry challenges
Turning to more familiar aspects of electronics, the two PCBs residing in the base are dedicated to power conversion and LED mounting, respectively. The power conversion is a 120V AC/DC conversion for the most part. The 12 WLEDS arrayed on the second board are arranged as two series strings of six WLEDs each. A specialty IC may be the controller for the switching power supply, but an additional feature of the LR6 may also hinge on the LEA001 "mystery part."
In the structure, where the lamps have been turned on you can see red LEDs between the arrayed WLEDS. These red lamps have been added to "warm up" the effective color temperature of the output to mimic incandescent, and their brightness is set by the light incident on the photodiode in the lower left part of the LED board. The photodiode is seen on the green patch. The system uses the diode to calibrate the red content by responding to generated WLED output, which itself can vary because of manufacturing variations.
The drive for widespread adoption of more efficient lights may not be a slam dunk however. CFLs have a limited lifetime of their own and LEDs at present are far too expensive to move mainstream. Achieving the broad-spectrum color-temperature aesthetics of incandescent with either CFLs or LEDs remains an elusive goal. Lumens per watt for both options are clearly superior to common light but the "peaky" aspects of CFL and LED output still leaves me a little cold. A green form of white light may be getting closer but when I'm reading or working on a crossword, I'll still be turning on a tungsten-filament bulb.
- David Carey