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There are two groups of patients who react abnormally to light: those whose diseases are induced by UV/IR or visible light (the photodermatoses) and those who have a pre-existing skin condition which is made worse by light.
1. Some photodermatoses have an internal cause and can be inherited or immunity based. Inherited photodermatoses are a rare group which includes, for example, xeroderma pigmentosum (XP). Exposure to UVA/UVB is associated with an increased cancer risk in XP so patients are advised to avoid all sources of UV, including CFLs and unfiltered halogen bulbs.
Another group of photodermatoses have no known cause but are increasingly thought to be based on immune responses. The part of the spectrum that plays the main role is UV light, so the main concern is with light sources that emit UV, such as CFLs. The severity of these diseases varies widely between patients and the amount of UV required to produce symptoms is also variable:
Some photodermatoses don’t have an internal cause but instead, are induced by medicines or other chemicals. Many drugs can make people sensitive to light. In the majority of cases, the drug together with light starts photochemical reactions that make toxic levels of products. A smaller number of drugs sensitize the immune system instead. The effects depend on the drug but common symptoms are changes in skin pigmentation, blistering or redness.
Some medical treatments exploit the photosensitizing ability of chemicals and this is used for instance in anti-cancer drugs. People undergoing anti-cancer photodynamic therapy are intentionally given photosensitizers and they can have skin flares if exposed to light so they could have reactions from CFLs and LEDs. However, these patients are very aware that they need to take precautions.
2. Photoaggravated dermatoses are a large and diverse group of diseases that are made worse by light but also arise without exposure to visible or UV light. Sunlight affects only a small proportion of people with these diseases and the skin of most patients seems to react normally to UV and visible radiation. The role of artificial light in these diseases is unknown but is unlikely to be significant. More...
About 1.5 million people worldwide have some type of inherited disorder where the retina degenerates over time and, in terms of diseases, fall within a range from Retinitis pigmentosa (RP) to macular dystrophies. Patients with RP first lose night vision followed by lateral vision and, in the late-stage of this disease, vision is restricted to a narrow central cone. In macular diseases, central vision is lost but side vision remains good. There are also intermediate diseases where there is some loss of both central and side vision. The age at which symptoms start, the speed at which the disease progresses and the final outcome are all variable.
The effect of light on these patients depends on the specific mutation that has caused the disease. For instance, two forms of macular dystrophy (Ogushi disease and Stargardt disease) are aggravated by light and Stargardt disease is particularly affected by blue light, but this is not the case for other diseases. Since patients don’t know which mutation they carry, they are advised to avoid unnecessary exposure to light. More...
The intensity of some light sources goes up and down regularly and, if this oscillation is sufficiently slow, it is perceived by the human eye as flicker. Flicker depends mostly on the light source but is also affected by other factors such as the field of view and whether or not the person is moving.
Obvious flicker has been implicated in conditions such as epilepsy. However, lights that flicker too quickly to be noticed, can still cause headaches and eye strain.
Early fluorescent lamps flickered very noticeably but modern lamps are much better. However, flicker varies considerably from one lamp to another depending on the design so one cannot draw general conclusions.
Light from LEDs is usually flicker-free, but some poor quality LEDs do flicker, particularly if they are used together with a dimmer.
There is no scientific evidence that non-skin conditions such as Irlen-Meares syndrome, myalgic encephalomyelitis, fibromyalgia, dyspraxia, autism or HIV are worsened by exposure to light from CFLs. However, experiments using other light sources and epidemiological studies are needed before one can draw final conclusions. More...
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