Effets sur la santé de la lumière artificielle

2. How do artificial lights work?

Fire has long been the only source of artificial light and today still, a large portion of the world’s population uses fire as their primary light source. Humans discovered fire early on in their history and used burning or heated materials as light sources. Today, approximately 1.6 billion people still use flame-operated lamps.

The first electrical light sources were also based on heating a substance until it glowed and this is how incandescent lightbulbs (carbon or tungsten) work. Halogen lamps are a modern type of incandescent source where the tungsten filament is contained inside a tube filled with a mixture of gases. One of the gases is a halogen and allows the tungsten to get very hot without melting. This makes the lamp more efficient and long-lasting and the light is brighter and closer to the colour of daylight, which is better for vision.

When electrical current flows through a gas, it can emit visible light and this process is used to make electrical discharge lamps. The basic design is a tube filled with gas and with an electrode at either end so that an electric arc can be sent between them. The actual light emitted depends on the pressure and the nature of the gas. Low pressure discharge lamps are very efficient but some models are bad at showing the natural colours of objects, as is the case for the yellow sodium lamps sometimes used for street lighting.

Fluorescent lamps are a specific type of low-pressure lamps where the visible light is produced by the phosphorous coating inside the tube that glows in response to the intense UV-light produced by the mercury vapors inside. Fluorescent lamps are cheap, long-lasting, efficient and very good for illumination. Compact fluorescent lamps (CFLs) consist of two, four or six small fluorescent tubes mounted on a base. They are very efficient and work in a similar way to conventional fluorescent lamps. High-pressure gas discharge lamps produce intense light. They are used in very specific applications and rarely in conventional indoor lighting. Flash lamps are designed to produce bursts of extremely intense light and are used mostly in photography, scientific, medical and industrial applications. Dielectric-barrier discharge lamps are also used in industry.

Solid state lighting is a new technology that could become dominant in future:

• Light-emitting diodes produce light by a process called electroluminescence. Although LEDs are coloured, it is possible to combine several LEDs to produce white light. Today, low-power LEDs are used for signs, indicators and Christmas lights. High-power LEDs are used for lighting.
• Organic light emitting diodes produce flat panel displays with brightness and sharpness that is impossible to achieve in any other way, but this technology is still in the early stages.
• Field emission devices are based on the same principle as the luminescent material used in TV screens. These lamps are 4 to 5 times more efficient than existing lamps, do not contain hazardous materials, have long life spans and can be made to produce light similar to daylight. This technology is still at the experimental stage but expected uses are indoor lighting and projectors.

It is difficult to pinpoint the “typical” spectrum emitted by a type of lamp because individual designs vary. It is for this reason that each individual model of lamp needs to be classified according to the specific risks posed to health. This classification is made according to a number of health effects, as four risk groups (RG):

• RG0 (exempt from risk) and
• RG1 (minor risk) lamps are not hazardous during normal circumstances.
• RG2 (medium risk) lamps do not pose hazards because we naturally move away from lights which are too bright or too hot.
• RG3 (high risk) include only lamps where a short-term exposure poses a hazard.

This classification is based on short-term exposures responses and applies only to individuals of normal sensitivity.

The majority of lamps used for normal lighting conditions are RG0 and most of the rare exceptions are RG1. Provided that these lamps are used at the distances for which they were intended, the UV, IR or blue light radiation they emit should pose little or no risk to non-photosensitive people. Halogen lamps are intended to be used with an external glass filter and they should also be non-hazardous, provided the filter is actually used. More...