1. Introduction - What is light?
The SCENIHR opinion states:
3. SCIENTIFIC RATIONALE
The purpose of this opinion is to determine if the proposed phasing out of incandescent lamps and their replacement with the more energy efficient Compact Fluorescent Lamps (CFL) can have possible health consequences for especially “light sensitive” groups of people. The CFL are technologically developed from conventional fluorescent lamps and differ mainly from those in size, in that they can directly fit into regular light bulb sockets, e.g., in desk lamps in close proximity to the user.
The objective of this section is to establish the scientific rationale which is necessary for providing an opinion in response to the request to the Committee. The section summarizes physical, engineering, biological, and medical scientific knowledge which is relevant for evaluating if there are specific health risks associated with CFL compared to conventional forms of lighting.
Light is defined as the electromagnetic radiation with wavelengths between 380 and 750 nm which is visible to the human eye. Electromagnetic radiation, such as light, is generated by changes in movement (vibration) of electrically charged particles, such as parts of ‘heated’ molecules, or electrons in atoms (both processes play a role in the glowing filament of incandescent lamps, whereas the latter occurs in fluorescent lamps). Electromagnetic radiation extends from γ rays and X-rays through to radio waves and to the long radio waves. This is often referred to as ‘the electromagnetic spectrum’ which is shown on the figure below (modified from American Chemical Society 2003):
An alternative physical description of light is to consider radiation as being emitted as discrete parcels of energy, called photons, which have dual nature – that of a particle and a wave. The fundamental parameter that distinguishes one part of the electromagnetic spectrum from another is the wavelength, which is the distance between successive peaks of the radiated energy (waves). Photons’ energy levels are determined by measuring their wavelength (expressed in units of length and symbolized by the Greek letter lambda λ). Of the two waves shown below, the left one has a wavelength that is two times longer than the one shown on the right:
The energy of a photon is directly proportional to the photon’s frequency, and inversely proportional to its wavelength. Frequency is measured in number of cycles (wave peaks) per second and is expressed in Hz. So, γ rays consist of very high-energy photons with shorter wavelengths and higher frequencies compared to radio waves.
In addition, light is characterized by its intensity. For example, the blindingly intensive red light on a theater stage may consist of photons of the same energy and wavelength as the red stoplight at a street corner; however, stage light is different in terms of the quantity of photons emitted. The higher the number of photons irradiated, the higher the amplitude (the height) of the wave of these photons. The figure below shows photons of the same wavelength (λ), frequency and energy which have two different levels of intensity:
The amplitude is a quantitative characteristic of light, while wavelength (intrinsically linked to photons’ energy and frequency) characterises the nature of light qualitatively.
Light is a very small component of the electromagnetic spectrum and is the part that can be perceived by the human eye. Radiation just beyond the red end of the visible region is described as Infra-red (IR), and radiation of shorter wavelength than violet light is called Ultra-violet (UV). The UV portion of the spectrum is divided into three regions:
Sunlight is attenuated as it travels through the earth’s atmosphere. This means that all radiation with a wavelength below 290nm is filtered out before it reaches the earth’s surface.
Characteristic for every light source is its spectrum, i.e. a graph of the radiant energy emitted at each wavelength. Depending on the characteristics of the light emitting system, the emitted spectrum can be broad or it can have sharp ‘lines’ at certain wavelengths; the former is the case for the sun, for incandescent and halogen lamps, and is related to the temperature of the source. The latter is usually related to specific changes in energy levels of electrons in certain atoms. Lamps used in lighting applications need to cover the visible range of wavelengths for proper white perception. By the physical principles of light generation, thermal sources like heated filaments of different types [historically C-fibre, W-filament, ‘Halogen’ protected W-filaments, and electrically induced high temperature plasmas (arc lamps)], as well as the sun and other stars, generate a spectrum of a so called ‘black body radiator’ which peaks at a certain characteristic frequency corresponding to the temperature of the emitter and follows a well described spectrum between the reddish glow of charcoals (~1000°C) and the white light corresponding to the surface temperature of the bright sun (~6000°C). Various spectra are generally recognised by their characteristic colour by a human observer. For example, due to an increase in scattering of short wavelengths (i.e. blue light) with an increased path length of the sunrays through the atmosphere, the sun takes on more and more of a red hue as it sinks toward the horizon.
Light is indispensable to life on the planet and consequently affects humans and other creatures alike. Notably there are important physical effects through the interaction of light with our skin and our eyes leading to the ‘warm’ (red light) and ‘cold’ (blue light) sensation as well as the side effects through our accommodation to the periodic changes each day and with the season which contribute to the regulation of activity/rest cycles.
In general, only scientific reports that are published in English language peer-reviewed scientific journals are considered. Due to the specific questions and the sparseness of primary scientific literature in certain areas, we considered other sources of information. We have furthermore included some information regarding certain additional conditions, and their possible link to fluorescent lighting, beside the ones specifically mentioned in the Terms of Reference.
To evaluate the scientific evidence supporting the various claims of correlations between fluorescent light from traditional fluorescent tubes and CFL and disease conditions, a set of criteria were used. These criteria are:
(i) case-control study, cohort study or provocation test involving a number of individuals, published in the peer reviewed literature;
(ii) findings confirmed by other studies in the scientific literature;
(iii) biological plausibility of cause/contributor and effect;
(iv) observations by a health professional in the relevant area;
(v) experiences described by individuals;
(vi) experiences by individuals reported by others;
(vii) substantial exposure and no evidence of adverse effects.
These criteria were then used to perform the ranking of evidence according to the following:
Criteria used to evaluate and rank the scientific evidence
Ranking A B C D E sufficient evidence some evidence inadequate evidence anecdotal evidence only no reported effects Criteria (i), (ii) & (iii) (i) & (iii) (iii) & (iv) (iv), (v) or (vi) (vii)
Source & ©:
3. Scientific Rationale, p. 10 - 12