LED vs. Traditional Lighting: Its Effect on the Human Eye
With the evolving technology of SSL (solid state lighting), many questions regarding the advantages or disadvantages of LED lighting as opposed to traditional filament lighting sources have emerged. To date, there has been little to offer as LED lighting has been one of those “mysteries” that few have ventured to unravel as it relates to the overall effect on the human eye.
The use of artificial lighting has always managed to ignite controversy as to exactly how healthy it is and whether or not the light emitted is considered to be safe to humans. One of the classic and common concerns involves warnings from the Health Protection Agency regarding single envelope CFL lamps and excessive UV light exposure by the Agency for Food, Environmental and Occupational Health & Safety (ANSES) study into a few LED lighting products. In these studies, the intent was to discern whether or not blue LED lighting creates a light hazard. One of the critical issues facing the lighting industry is a debate as to whether it should place healthy and safe lighting high on its agenda when designing lighting.
The apparent lack of knowledge on healthy and visually safe lighting is prevalent in the industry. Additionally, the overall effects of LED lighting are rarely mentioned or discussed outside of academic circles. This paper will attempt to identify a few of the many critical health and safety issues associated with artificial lighting with the aid of several published documents.
The use of artificial lighting has laid claim to a wide range of light sensitive symptoms that are aggravated by their use to include the following:
- Myagic Encephalomyelitis (Chronic Fatigue Syndrome)
- Irlen-Meares Syndrome (Scotopic Syndrome)
- Autism/Asperger Syndrome
- Retinal diseases such as age-related macular degeneration (AMD)
- Chronic Actinic Dermatitis
- Solar Urticaria
Visible light is defined as the electromagnetic radiation with wavelengths between 380nm and 750nm which is mostly detected by the human eye. Electromagnetic radiation exists from gamma rays right through to radio waves as shown in figure 1 with the visible wavelengths occupying a small section of the spectrum. In addition to wavelength, light can also be characterized quantitatively by its intensity.
The ultra-violet portion of the spectrum (fig 1) can be particularly dangerous to humans and is usually divided into three regions:
UVA (315nm – 400nm)
UVB (280nm – 315nm)
UVC (100nm – 280nm)
Each artificial light will have its own unique characteristic fingerprint and that is often referred to as the Power Spectral Density (PSD) or spectrum curve which identifies the amount of radiant energy at each wavelength. For example, in last month’s article we use the spectrum curves to determine the Correlated Color Temperature (CCT) and Color Rendering Index (CRI) of an LED light source.
Depending on the characteristics of the light emitting system, the emitted spectrum can be broad or it can have sharp ‘peaks’ at certain wavelengths; the former is the case for natural sunlight and the latter is for incandescent, halogen and certain types of LED lamps where the spectrum will contain peaks of radiant intensity at certain wavelengths.
A fluorescent lamp generates light from collisions in a hot gas (‘plasma’) usually containing mercury which emit photons at two UV emission lines (254nm and 185 nm). The created UV radiation is then converted into visible white light by UV excitation of a fluorescent coating on the inside of the glass tube. The chemical composition of this coating is selected to emit in a desired spectrum for example warm white lamps may use three part phosphors. For example, fluorescent lamps can be enriched for blue light (wavelengths 400-500 nm) in order to simulate daylight better in comparison to incandescent lamps. Like fluorescent lamps, CFL emit a higher proportion of blue light than incandescent lamps.
The vast majority of LEDs use a similar principle but instead use a blue LED coated in a phosphor material to generate the white light. The advantage of LEDs as a light source is the pump wavelength is around the 470nm wavelength +/-20nm and therefore does not contain UVA, UVB or UVC wavelengths that are harmful.
Effects of Light – Epilepsy
Five percent of the total world population has single seizures, and the annual incidence is 50 in 100.000 (WHO 2001). About five in 100 of epileptic people have photosensitive epilepsy. Photosensitive epilepsy is a form of epilepsy in which seizures are triggered by visual stimuli that form patterns in time or space, such as flashing lights, bold, regular patterns, or regular moving patterns.
The visual trigger for a seizure is generally cyclic, forming a regular pattern in time or space. Flashing or flickering lights or rapidly changing or alternating images are an example of patterns in time that can trigger seizures.
While photosensitivity of epileptics has scientifically been proven there are few studies which determine if the flicker frequency range > 120 Hz causes seizures.
All artificial lighting systems suffer from flicker however the frequency of the flicker will depend on the technology. For example incandescent lamps would have a frequency similar to that of the mains frequency however high frequency ballasts are now used on fluorescent tubes which have switching frequencies in the 20-90kHz range.
Effects of Light – Migraine
Migraine can be defined as an intense pulsing or throbbing pain in one area of the head. It is often accompanied by extreme sensitivity to light and sound, nausea, and vomiting. Migraine is three times more common in women than in men.
It is estimated that 14% of adults suffer from migraine (Stovner et al. 2006). According to self-reported information, certain visual patterns can reliably trigger a migraine attack, such as high contrast striped patterns or flickering lights. Fluorescent lamps can cause eye-strain and headache (Wilkins et al. 1991). Patients with migraine show somewhat lowered flicker fusion thresholds during migraine-free periods. In addition, photophobia, which is an abnormal perceptual sensitivity to light experienced by most patients with headache during and also between attacks, is documented in many studies.
The good news is that several groups are looking into the effects of flicker including the IEEE PAR1789 standards group which is recommending practices for modulating current in High Brightness LEDs for mitigating health risks to viewers. You can see more from this group on their website www.grouper.ieee.org/groups/1789/. Also Nema discusses flickering within NEMA LSD 49-2010 entitled “Solid State Lighting for Incandescent Replacement—Best Practices for Dimming” available free at www.nema.org/stds/lsd49.cfm
Artificial Light in general does not pose too much of a hazard. However certain lighting technologies offer the opportunity to improve quality of lighting from a human visual perspective by increasing the flicker frequency and flicker percentage. I suggest if you want a healthy LED lighting system for your clients invest in quality and procure a lighting system with high switching frequencies and preferably uses DC outputs with low ripple current rather than switched frequency outputs.
Currently there are thousands of replacement T-8 4000K, LED tubes in use in at least two major Universities located in Syracuse, NY. It was discovered in one instance after an installation at LeMoyne College that the incidents of leaves associated with fluorescent induced migraine headaches was mitigated by at least 80%.
Therefore, the conclusion of this author, based upon the most updated and current data available is that LED replacements for traditional fluorescent lighting in commercial, industrial and institutional applications is clearly an advisable alternative on many levels. First and foremost, medical considerations should be front and center with respect to retrofitting existing fluorescent lighting with less harmful LED lighting.