Facts About Light
- Visible light is that part of the electro-magnetic spectrum that lies between the wavelengths of ultraviolet and infrared.
- White light is all colours: a rainbow is white light split up into its component colours.
- Sunlight contains, more or less, equal portions of all colours of visible light, ultraviolet (UV) and infrared.
- Northern sunlight (i.e. in areas north of the fortieth parallel) has more blue and UV than equatorial sunlight because of the greater absorption of all other colours, or wavelengths of light, by the atmosphere.
Forms of Artificial Lighting
Incandescent (or Tungsten) Lighting
These are the most universal screw-in or bayonet bulbs in most homes consisting of an incandescent bulb with a tungsten filament in a near vacuum. Incandescent light is biased heavily toward the red spectra.
Advantages: Low cost for initial purchase.
Disadvantages: Inefficiency, low output of light for energy level.
Effect on light sensitive patients: Generally safe although very light sensitive individuals may need to avoid high wattage bulbs.
Halogen Bulbs
A variation of the incandescent bulb, it involves a more complex process whereby UV generated by the inner capsule is filtered by the outer capsule. Halogen lamps are 25-30% brighter than regular incandescent bulbs and remain brighter, longer.
Advantages: Efficiency. They last about twice as long as regular incandescent bulbs and give off 95% of their initial light output at the end of their lives.
Disadvantages: They are on average 5 to 10 times as expensive as their non-halogen counterparts.
Effects on light sensitive patients: Many report a severe adverse reaction to halogen bulbs, as they emit more UV and blue light than their Tungsten counterparts.
Fluorescent Lighting
They emit about four times as much light per unit of electricity as incandescent lights but are more complicated to install. The mechanism of fluorescent lighting involves the emission of UV and E-field radiation. Fluorescent tubes come in hundreds of shapes, sizes and spectral output.
Advantages: Cheaper to run.
Disadvantages: More expensive to install.
Effects on light sensitive patients: Because fluorescent lighting involves the emission of UV radiation it is unsafe for light sensitive individuals (unless covered by protective film) and for many, unless the ballast is at least 5m from the sufferer.
HID (High Intensity Discharge) Lamps
These are the big bright lamps you see in grocery stores, street lighting and industrial lighting. These lamps produce a lot of light quite efficiently.
- There are three types of HID lamps:
- Mercury Vapour: has a decided bluish cast (particularly unsafe for light sensitive patients).
- Metal Halide: contains all the spectra (so not suitable for light sensitive patients).
- Sodium Vapour: emits monochromatic (pure) yellow light.
Advantages: Sodium Vapour lamps are ten times more efficient than incandescent bulbs, in fact these are the most efficient bulbs made and one of the cheapest HID bulbs to purchase.
Disadvantages: Yellow tone of light.
Effect on light sensitive patients: This spectral range has no adverse effect and can safely be used for floodlighting and lighting of public places.
LEDs (Light Emitting Diodes)
Heralded as the lighting of the future, it is predicted to be the standard form of lighting in 10 to 15 years because it is the most efficient form of lighting to date.
Advantages: Very economical, with the most long-lasting bulbs.
Effects on light sensitive patients: LEDs are available according to exact colour specifications, measuring wavelength nanometres - blue, green, yellow, red - or a combination giving white light. We would be most comfortable with yellow LED's and would need to avoid blue. Unfortunately most LEDs presently produced emit far too much blue light, and are as dangerous as fluorescents.
Planning for the Future
It is important that while LEDs are in the developmental stage our difficulties and requirements are brought to the attention of manufacturers and public and private sector planners. This could eliminate the expense and complications of disability access adaptations at a later stage. More efficient incandescent bulbs are being researched by all major manufacturers.
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