Sunday, 29 March 2009

3i. CFL Analysis - Conversion Charts

European recommendations

In Europe, CFLs are often claimed to give "5 times more light" (or "up to" 5 times more, to cover poorer performing covered, reflector and decorative bulbs). Optimistic calculations on potential savings are almost always made on the nominal initial lumen/watt values of the best performing bare tubes. A typical European equivalence chart may look like this:

These recommendations are, however, quite misleading as those who follow them will get less light than they originally had! Astonishingly, this EU Quality Charter for Fluorescent Lamps accepts lower minimum initial claimed lumen output from an equivalent CFL than what a typical incandescent bulb usually gives (first two columns of this table):

As can be seen in the last two columns (which I've added for comparison) incandescent ("GLS") lamps usually have a higher lumen output than minimum EU requirements for equivalent CFL! [1]

If a typical CFL does not produce as many initial lumens as the lamp it is supposed to be replacing, it cannot possibly be said to give "5 times more light" of incandescent energy use.

Light Reduction

As explained in under Life Span, CFLs give even less light as they age. After 2000 hours, the EU Quality Charter accepts a 12% light loss for bare CFL tubes, 17% for covered CFL bulbs, and 25% for both types at the end of their life.

To illustrate how this works out in lumen output for various wattages, I've used lumen figures from manufacturer catalogues [1, 2, 3] for standard incandescent (GLS) A-lamps and a typical good quality CFL bare tube. In the following columns I've deducted the permitted 12% and light loss after 2000 hours and the actual mean light loss for recently tested CFL tubes of the same brand after 6000 hours [4]:

Here I've deducted the permitted 17% and 25% light loss for double envelope CFL bulbs (a real test showed 15% and 27% for this particular model). [5] In the manufacturer's catalogue, it is sold as "saving 80% light" (= giving "5 times more light" than an incandescent) but as we can see here, it is less than with light loss included in the calculation.

To get the same lumen output as from an incandescent bulb, and to compensate for the expected reduction in output as the CFL ages plus the poorer light quality, one needs to choose a higher watt CFL than usually recommended (just like professional lighting designers often do when installing new lights, as they are well aware of these factors). This will, however, give a light that may be too bright and glaring in the beginning and too weak and dull towards the end of its life.

Thus, when used in real situations, an Energy Class A-rated, good quality CFL bare tube does not give 5 times more light, but 3-4 for some of the most effective CFLs on the market. Covered CFL bulbs give somewhat less initially and lose more as they age (a mean of 25% loss for Philips and Osram bulbs, and 30-100% for IKEA bulbs in 2008 test). [4]

1. Philips Lighting
3. Hawells-Sylvania
4. Råd & Rön 1/2008
5. Råd & Rön 7/01

North American recommendations

U.S. and Canadian ENERGY STAR requirements stay more reasonable and require a minimum initial lumen output that roughly translates to a 3:1 or 4:1 switch. [1, 2]

Again required initial lumen output is slightly less than incandescent output (at 120V incandescent lamps give more light) and light loss is not taken into account, despite General Electric being more open and giving mean lumen values in their online catalogues.

As can be seen in the above example, a fair switch is closer to 3 than 4 for the most effective bare tubes, and of course less for covered bulbs, globes, reflectors and decorative bulbs. Yet on the same page, it is still claimed that "ENERGY STAR qualified bulbs use about 75 percent less energy than standard incandescent bulbs."

2. Canadian ENERGY STAR
3. GE Lighting


Based on manufacturer figures for initial lumens, with light reduction included, the best tubes give only 3-4 times more light in Europe and around 3 in the U.S.A and Canada. Less for covered, reflector & decorative CFLs, for CFLs used in the wrong luminaires, and for poorer quality CFLs of all types.

Consumers therefore need to be advised to choose a higher watt CFL than recommended to get as much light as from the original bulb and to compensate for the eventual light degradation and poorer quality of the CFL replacement. And the EU standardisation directive needs to be adjusted to reflect reality.

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