Yes, the scare quotes are necessary. For decades, “full-spectrum lighting” has been a popular but misunderstood topic. Its definitions vary but the basic idea is that electric lights that produce the same wavelengths of light as the sun will mimic the benefits: improved health, cognition, etc. “Full-spectrum lighting” allows us to imagine that being indoors can provide the same benefits and joys as stepping into a warm, sunny meadow.
Sales professionals who march door-to-door and store-to-store selling full-spectrum lighting believe they are providing a great resource that aids learning and performance. Indeed, the marketing of “full-spectrum lighting” is so successful that most people think it confers improvements over traditional fluorescent lighting.
The problem is: it does not. This has been amply demonstrated by review articles of the scientific literature that look over dozens of studies. Compiled by the National Research Council of Canada, they can be found here and here. While particular studies argue there is a benefit to “full spectrum lighting,” their methodology is often questionable and the preponderance of the evidence is stacked against them.
The reason for this is that “full-spectrum lighting” is a marketing concept (thus the scare quotes) not a rigorous scientific standard. Compared to traditional fluorescent lighting, “full spectrum lighting” does not improve student attendance or arithmetic scores or memory tasks. It is not better at treating Seasonal Affective Disorder (SAD) than regular fluorescents (more on this later). It will not reduce hyperactivity in children nor will it improve muscle growth.
From an energy perspective, full spectrum lights aren’t great, either. They actually use more energy than regular fluorescents. On average, full spectrum lights have a lower efficacy – “Lumens per watt,” think “Rays of light emitted per electricity used” – than traditional fluorescent bulbs. “Full spectrum lights” will therefore typically cost you more to operate and consume more natural resources than regular fluorescents. Just read the wattage on any lamp (aka. light bulb) you buy: no matter what anyone tells you, replacing a 32 watt lamp with another 32 watt lamp will not save energy.
“Full-spectrum lights” also sell at a premium compared to regular fluorescents. A hefty one, too: they can cost 5 times as much. Sometimes more.
The National Lighting Product Information Program (NLPIP) – an independent light testing laboratory supported by the government and utilities, not lighting manufacturers, provides a great example of lighting costs and the price premium of “full spectrum lights.”
As you can see in the chart at right (courtesy of NLPIP), the Spectral Power Distributions (the blue and green lines) of two different lamps look identical. That’s because the two lamps are producing almost exactly the same light. But one is called “full spectrum” for marketing and sells for $15 and the other is marketed as a regular fluorescent and sells for $6. Carbon Lighthouse has seen cases of perfectly good $2 lamps being replaced with $15 lamps because the pricier ones were “full-spectrum” and the institution believed they would improve performance and health.
What is a Spectral Power Distribution? It is a graph of the amount of light emitted by a light bulb for each individual wavelength of visible light. Blue lights have lower wavelengths (around 475 nanometers) while red lights are longer wavelength (around 650 nanometers). In the graph above you can see a peak at 440 nanometers, which is an indigo-blue. This means that both lamp types emit a relatively large amount of indigo-blue light compared to other colors. A full-spectrum light, by the most basic definition must emit at least some light for every visible wavelength of light that the sun emits.
This means that full spectrum lights are well-suited for applications where one lacks daylight but still needs light from every wavelength of the spectrum: i.e. an art museum or an artist’s studio. In those situations, it’s critical to be able to differentiate every hue. And in order to do so, you need a light source that can provide all those colors. The problem is, “full spectrum” lights do not necessarily do this any better than regular lights.
The way we measure what fraction of colors can be differentiated under a particular light is with something called the Color Rendering Index, (CRI), an important lighting concept. Sunlight and incandescent lights have CRI of 100, because under such light all the colors on a representative color palate can be differentiated by a roomful of experts. A CRI of 80, typical of most fluorescent lights provides lighting with more than enough color-determining accuracy for office, industrial, and school applications, but would not be ideal for an artist’s studio. So “full spectrum” lights with high CRIs have a limited place, but any light with a CRI between 90 and 100 would serve just as well, and you would save yourself the “full spectrum” price premium – and probably a bit of energy, too.
Seasonal Affective Disorder is another place where the concept of “full-spectrum” lighting pops up. Seasonal Affective Disorder is a well-substantiated condition, and various empirical treatments have been developed using lighting therapies. “Full spectrum” fluorescent lights, however, are no better a treatment than standard fluorescents (see here and here again) Research has shown, however, that lamps with a greater number of shorter wavelengths (blue, green, and yellow) do seem to produce better clinical outcomes than longer wavelength lamps (red).
Lighting research is an active and growing field, and with the rise of LED lamps, concepts like efficacy, CRI, and color temperature are important, quantifiable concepts. There will, unfortunately, also continue to be unsubstantiated and purely-marketing terms like “full spectrum lighting” that will promote neither health nor performance nor the environment. Even though their promoters say they do.
It is critical to use government and independent sources (the NLPIP, for example) and to trust salespeople or popular opinion only after reviewing the scientific research first. You can never ask too many questions nor request too many references.