Unlike incandescent lamps, fluorescent lamps require either a conventional magnetic ballast or an electronic ballast to regulate the flow of power through the lamp which would otherwise be destroyed. The main difference between these two types of ballast is the operating frequency. Whereas magnetic ballasts run at the mains frequency of 50 Hz, electronic ballasts convert the supply frequency to high frequency (25,000-40,000 Hz).
In other words, a lamp operated with conventional ballast goes on and off (frequency) at 50 times per second, which is often perceived as flickering. Lamps operated with electronic ballast flash on and off so frequently (25,000 to 40,000 times) that they do not appear to flicker.
It is known that flicker can be sensed in peripheral vision at higher frequencies than in foveal vision. This is noticeable when looking at an old TV sideways or when using a lamp with a conventional ballast for reading. Since the peripheral area of the retina is used in both cases, the light appears to flicker more. People with macular lesions (e.g. macular degeneration) often experience this problem since they use extrafoveal vision.
Solid state lighting (LED)
The most recent evolution in lighting is solid state lighting based on light emitting diode (LED) technology. Light is generated by discharge in a solid state material. By changing their orbitals, electrons “excite” other electrons that then fall back to their natural state, thereby releasing the energy surplus in the form of radiation. Although LED technology has been available for many years, it was only used in a few applications for a long time due to its modest luminous flux and monochromatic light quality. Applications included mainly signal lighting in control panels and traffic lights. Recent technological breakthroughs, however, have led to significant advances in performance, including the generation of white light, which has opened a whole new future for accent and general lighting applications.
Its key features are:
Generating white light with LEDs: By their very nature, LEDs can only generate monochromatic colours. Consequently, to create white light, two or more colours must be combined. One solution for creating white light with LEDs involves grouping red, green and blue semiconductor chips in a single LED, or closely aligning separate red, green and blue LEDs and optically mixing the emitted radiation. A more common approach uses phosphor coated LEDs that emit blue light. The coating converts part of the blue light into yellow light, which leads to the creation of white light. These white LEDs produce light temperatures from 2700 K to 8000 K. By applying multiple phosphor coatings, the blue light can be converted into additional colours, improving the colour rendering index to 80 and above, which corresponds to a rating of good to excellent.
LED lighting is surely one of the most significant innovations in the lighting industry since the invention of electric light. LEDs fundamentally change the nature of lighting, since they offer new options for using artificial light to enhance human perception. All low vision lamps from SCHWEIZER are equipped with tried and tested SMD LEDs. These are extremely small and have a long life.
Unlike energy-saving lamps that require a starter unit, LED lamps run on direct current. Consequently, neither flickering nor interference with other energy or light sources occurs. Proper layout of the LEDs and optimal positioning of the lamp ensures homogeneous illumination of the reading material and prevents glare.
Optimal, proper lighting can reduce the magnification power required, while improving reading speed and contrast sensitivity. This makes reading a more comfortable experience. Visually impaired people require optimal lighting, especially where they read or work, to make the best use of their (remaining) visual acuity.
It is therefore essential to select the light temperature and lamp that suit the visually impaired patient best when fitting and dispensing magnifying visual aids.
The OPTIK-AKADEMIE Training Portal offers a seminar on this topic consisting of several video tutorials:
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Further information on product solutions for visually impaired people is provided at www.improvision-lvs.com.