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CFL, LED lamps light up a 'green' world

Posted: 10 Oct 2008     Print Version  Bookmark and Share

Keywords:CFL  LED  WLEDs  electricity consumption 

The energy challenge nowadays is not only to "make more" but also to "use less." Despite the attention given to alternative energies to increase available power, measures intended to conserve energy present an equally important story.

Hybrid vehicles have received justifiable attention in the car industry's conservation effort and certainly automobiles are a big part of the energy puzzle. Home and commercial lighting also represent significant consumption, accounting for 15 per cent to 35 per cent of all energy use (depending on whose numbers you believe). The workhorse incandescent lamp, evolved over so many years, remains in widespread use to be sure, but abysmal efficiencies—typically well below 5 per cent—have spurred change.

Enter two technologies already helping and likely to grow as pressure mounts to reduce electricity consumption—the compact fluorescent lamp (CFL) and LED lamp. Both are moving towards, if not being legislated into, more widespread application in the search for conservation.

The former of these two has been on a steady march towards affordability, and Planet Analog editor Bill Schweber recently sent me a pile of CFLs, now available as sub-Rs.215.05 ($5) replacements for incandescent bulbs, as a not-so-subtle recommendation for a teardown.

But CFL is not alone, and Bill's hardware handout got me thinking more about the other contender in the game. LED lighting has made measured but steady progress as a viable replacement for the inefficient incandescent, and a high-brightness LED "downlight" recently brought to market caught my eye. We'll look at examples of both here.

Old dogs can learn new tricks

The fluorescent bulb is substantially more efficient than the incandescent alternative, producing greater direct light (and less heat) per input watt. Though long used in offices and other commercial and residential settings, fluorescent lamps didn't come in forms suitable for small-lamp replacement until the 1980s. The past couple of decades have seen miniaturised screw-in CFL bulbs finally achieve quite low price points, promoting consumer adoption.

The MaxLite bulb examined here is a 20-W lamp claimed to produce equivalent illumination to a 75-W incandescent. Like all of its traditional fluorescent peers, the MaxLite CFL uses a glass tube whose phosphor lining emits from UV radiation produced by ionised gas in the tube. The CFLs achieve miniaturisation 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 downsised supply to create a suitable lamp drive in relatively little space.

A pair of transistors, quartet of diodes, and collection of capacitors and inductors all come together to first rectify the AC power and create a follower resonant inverter circuit that generates 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 evolved 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.

Wearout of lamp phosphors remains an issue, and vent holes in the lamp-base enclosure suggest that heat-related wearout 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 seen its own transformation of late. 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 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 the princely sum of Rs.4,301.06 ($100), plus tax. Yikes! The price reflects the more limited nature of high-brightness LED production versus CFL. Simply put, a mix of technology lock-ups and the costlier production needed for the WLEDs means not everyone can pile on-yet-to drive costs down.

The LR6 produces a claimed lumen output equivalent to a 65-Watt incandescent lamp with a more miserly 12 W of input consumption, making it 80 per cent more efficient than the incumbent tungsten-filament bulb and roughly 50 per cent better than the CFL.

Construction of the light is driven in part by the retrofit nature of the LR6, which is meant to screw directly into a traditional can light's lamp base. However—and to my surprise—the housing is a substantial cast-aluminium, finned structure. This adds significantly to the costs and seemed like overkill in light of the minimal 12-W draw. I must be missing something there.

Familiar aspects

Turning to more familiar aspects of electronics, the two printed circuit boards residing in the base are dedicated to power conversion and LED mounting respectively. The power conversion here is a (120-V) AC-to-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 speciality 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 photo, where the lamps have been turned on you see red LEDs between the arrayed WLEDS. These red lamps have been added to "warm up" the effective colour temperature of the output to mimic incandescents, and their brightness is set by the light incident on the photodiode in the lower left corner of the LED board (the photodiode is on the green patch). The system uses the diode to calibrate the red content by responding to generated WLED output, which itself can vary due to manufacturing variations.

Not all's well in LumenLand

The drive for widespread adoption of more-efficient lights may not be a slam-dunk however, at least in my book. CFLs have a limited lifetime of their own and LEDs at present are far too costly to move mainstream. Perhaps more significant, achieving the broad-spectrum colour-temperature aesthetics of incandescents with either CFLs or LEDs remains an elusive goal. Lumens/watt for both alternatives are clearly superior to conventional 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 a crossword tonight, I'll still be turning on a tungsten-filament bulb.

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