This text is an excerpt from the essay:
Incandescent Light and HealthA medical appeal for healthy light by Alexander Wunsch, Heidelberg. If you are interested in the full article (in German), you can find it here: Glühlampenlicht und Gesundheit
The incandescent bulb creates a warm, cosy light – »but energy saving lamps can do that as well!« That´s the statement of those campaining for the banning of the incandescent bulbs these days. After all, compact flourescent lamps exist in different light colors – so those, who feel that the standard model creates a light that is too cool, can use the warm white version instead.
But if you compare the spectra of incandescent and warm white energy saving lamps, it is easy to see that there is a huge difference. If you follow the theory of the international illumination committee (CIE), the human eye should not be able to detect this difference – but that´s pure theory and might be far from practical reality. Numerally, both light sources have the same color temperature, 2700 kelvin, so where is the problem?
It starts with the fact that there is two different ways of measuring the color temperature: Either in the way that´s conventional in physics, which is a stepless measurement across the whole relevant spectrum, or in the way commonly used in light engineering since 1931, which is a three point measurement following the definition of the standard viewer. This standard viewer is defined to have the highest sensitivity for color recognition in three specific wavelengths; 700nm for red, 546,1 nm for green and 435,8 for blue. The last two wavelengths are adjusted to two spectral lines of mercury, which is to say that the standard viewer is calibrated two-thirds to mercury.
All in all, it is visible that the system based on the standard viewer defined by the CIE in 1931 is full of simplifications and compromises. It is nor surprising therefore, that from a medical and biological viewpoint, it is not suitable to describe light sources in a way that can determine the full scale of physiological reactions and perception.
As long as it is clear that the indication of color temperature on the packaging of a lamp doesn´t refer to the biological quality of the emitted light, there is no problem.
But when the correlated color temperature is used to explain that the spectrum of an incandescent bulb and a warm white energy saving lamp are comparable, that is where the deception starts, because in effect, you are comparing apples and oranges.
The hight of deception is reached, when mercury light is sold as healthy “bio-light”.
Alexander Wunsch, physician and photo-biologist, Heidelberg, GERMANY, firstname.lastname@example.org