Sunday, 29 March 2009

3a. CFL Analysis - Light Quality

When it comes to light quality, there exists no replacement for the incandescent lamp, other than mains voltage halogen in retrofit bulbs - most of which are also being phased out!

What is so unique about incandescent light then? * Unlike other light sources, incandescent and halogen lamps are tungsten black-body radiators, a version of fire-light which humanity has evolved with since fire was discovered. Like sunlight, incandescent light has the highest possible colour rendering (CRI 100), due to naturally continuous spectrum, and a warm-white, human-friendly light which radiates and makes colours come alive.

Update 25 june: Lighting designer Ed Cansino in a recent, highly informative interview:
"...if I were forced to choose the best lighting for residential overall, it would have to be incandescent. I feel that we as humans have had a deep connection to flame for many thousands of years. It’s almost like it’s in our DNA. It’s interesting that as time moves on, people are still drawn to sitting around the camp fire, a fireplace, even a barbecue. Think of a Yule log. It’s just that this particular quality of light is ingrained in us. You can even get a screen saver of log flames. Incandescents with their glowing filaments are a form of flame and are thus an extension of this inborn affinity that we have for fire."
* When dimmed or used at lower wattages, the light colour gets proportionally warmer and more like candle light. Increase brightness and it gets whiter again. This is how a natural light source behaves.

* Icandescent light is the standard against which all other types of light is measured. This is why the lighting industry has put so much effort into trying to copy its light colour, colour rendering capacity and other qualities.

* CFLs are based on a completely different technology, and LEDs on yet another. Even if the industry can now mix phosphors to decently emulate incandescent light at a superficial level in some of the best brand models, FL/CFL or LED light is no more the same thing as incandescent light than a gold-coloured alloy can be called real gold, or synthetic microfiber real silk. Both have their respective uses, but in many cases a substitute just won't do. CFL light is a composite light, an artificial replica of the real thing that just doesn't feel the same and does not behave in the same way. When dimmed, for example, it just turns cooler and more grey and dull, not warmer.

See this interview with a pro-CFL professor explaining the quality problems with CFLs: Why Efficient Light Bulbs Fail to Thrive

Here are spectral distribution charts (from Osram) for different light sources, which illuminate the quality differences very clearly:
 Incandescent light with continuous spectrum and full colour rendering (CRI 100).

Example of standard FL/CFL with uneven spectrum & limited colour rendering (CRI 82-85).

White LED, a smoother curve but peaking in the blue end of the spectrum instead of the red.

Ron Rosenbaum describes the difference more poetically:
"I've tried the new CFLs, and they are a genuine improvement—they don't flicker perceptibly, or buzz, or make your skin look green. There is a difference, and I'd be in favor of replacing all current fluorescent bulbs with CFLs. But even CFLs glare and blare—they don't have that inimitable incandescent glow. So don't let them take lamplight away. Don't let them ban beauty.

"Don't get me wrong, this is not a plea for Ye Olde Times, for gaslight and quill pens. It's just a plea not to take for granted the way we illuminate our world. Not all change is improvement. Why do I put such a premium on incandescence? For one thing, I am a bit romantic about it. A lamp fitted with an incandescent bulb and dim translucent shades casts a lovely, painterly glow on human faces, while the light of fluorescents recalls a meat locker.

"Why do you think there is such artistry to so many lampshades? They are the lingerie of light.

"But the appeal of incandescence is not just a matter of romance. I suspect there are also answers to be found in the physics and linguistics of incandescence.

"I'd speculate that it has something to do with the different ways light is created by incandescents and fluorescents. Incandescent light is created by heat, by the way an electric current turns a thin metal filament (usually tungsten) red then white hot in a transparent or translucent globe filled with an inert gas that prevents the filament from burning up, allowing it to give off a steady glow. (That explains the warmth: The fact that incandescence emanates from heat creates warmth, distinguishes it from the cold creepiness of fluorescence.)

"Fluorescent light bulbs, on the other hand, are coated inside with chemical material that lights up as energy reaches the tubes. (It's a bit more complicated than this, but that's the general idea.) Fluorescents sometimes appear to flicker because alternating current brings that energy to the bulbs in pulses, rather than steadily. In incandescents, the hot filament stays hot—and therefore bright—despite alternations in current; it can't cool fast enough to dim or flicker.

"The new CFLs pulse faster than their ancestors, so the flickering is less perceptible, but at some level, it's still there. CFL manufacturers may be right that the new bulbs are an improvement, but there is still something discontinuous, digital, something chillingly one-and-zero about fluorescence, while incandescent lights offer the reassurance of continuity rather than an alternation of being and nothingness."

Who wants to have a romantic dinner in the dull gloomy light of a CFL? Why do lighting designers of usually choose halogen, incandescent, high-pressure sodium or metal halide for shops, hotels, restaurants etc. when they want to create an attractive environment, and so rarely CFLs?

Most likely because they are well aware of the fact that even the best incandescent-mimicking warm-white CFLs give a dull, non-radiating light which makes colours look pale and dead due to lower colour rendering (CRI 82-85), spiky spectral distribution (lacking parts of the spectrum - check this out for yourself with the back of a CD and see the spectrum broken up into 3 blocks with all the wavelenghts inbetween more or less missing) and lack of radiance and glow.

And that's not mentioning all those odd coloured ones which still dominate the lower end and some of the high end of the CFL market (according to recent consumer tests).

Lighting designer Gad Giladi, D.E.S.A., M.F.A. FPLDA, explains what happens when wavelenghts are missing:
"Not only are the quantities of light of CFL 'equivalents' not equal to those of the planned replaced incandescents but also the quality of the light greatly differs. This is due to the fact that the spectrum of the incandescent is a continuous one, i.e. has energy in all wavelengths of the visible electromagnetic spectrum while the spectrum of the CFLs, like all discharge lamps is a discontinuous one, i.e., depending on the composition of the phosphor coating of the tubes will present a lack of or a deficiency in energy at certain wavelengths of the visible spectrum.
"This characteristic is not immediately visible to the human eye until the emitted light falls on a surface or an object: the energy in each different wavelength corresponds to a colour perceived by the human visual system. If that colour does not exist in the light, its corresponding pigment in materials cannot be perceived by the eye; if the energy in a specific wavelength is deficient, the corresponding pigment in materials will be perceived as dead, washed-out and distorted. (...)

"That means that where colour perception is important, i.e. everywhere the human being lives and spends time, the replacement of incandescents by CFLs is going to inevitably create dull looking spaces, distort colours of architectural finishes (stone, marble, timber, paint, stucco etc.), of furnishings – curtains, carpets, upholstery, furniture finishes, artwork etc.), warp the colour of skin (people are continuously going to look bad/sick in their mirrors as well as in the eyes of their partners).

"Incandescent lamps are close to theoretical 'point sources' which allow for the design of precise optical systems around them to direct the light in an accurate manner. This permits the creation of accent lighting, a means to create visual interest and drama in spaces. CFLs are diffuse light sources and no engineering will truly make a diffuse light source into a 'point-source'. Gone is accent lighting!"

Lighting designers against incandescent ban (for both light quality and environmental reasons):

IALD - International Association of Lighting Designers
IALD Statement

PLDA - Professional Lighting Designers' Association
PLDA Statement

Kevan Shaw Lighting Design
Summary of points against the CFL

Michael Gehring, Principal of KGM Architectural Lighting
Gehring statement

Jeff Miller, President-elect IALD, Director of Pivotal Lighting, statement

Scott Yu, Principal, Chief Creative Officer of Vode Lighting
Yu statement

There are both visible and measurable differences in quality between incandescent light and the light from even best CFLs and LEDs on the market.

Banning a top quality product in favour of a totally different and quality-wise inferior product is like banning wine with the argument that "wine-lovers can just as well drink cider: practically the same thing" because both are mildly alcoholic beverages with a superficial similarity.

FL/CFL light may have its use where lamps are left on all day and quantity matters more than quality, e.g. at work, in public building corridors etc, but not necessarily in retail, hospitality and domestic environments where consumers expect a more attractive and/or relaxing light.

Light is like air, food and water - it's essential to our well-being, and quality matters!

Lighting is also one of the most powerful mood-enhancers, can markedly affect how environments are perceived, as well as both comfort, well-being and health.
For this reason, I'm sure many would be willing to pay a little extra for top quality light just to still have choice.

No comments:

Post a Comment