Fundamentals of lighting Visible – Invisible Lights:
Energy in the form of transverse magnetic and electric waves. In a vacuum, these waves travel at the speed of light (which is itself a form of electromagnetic radiation). The acceleration of electric charges (such as alternating current in a radio transmitter) gives rise to electromagnetic radiation. Other common examples of electromagnetic radiation are x-rays, microwaves, and radio waves.
NATURE OF LIGHT
Light is energy in the form of electromagnetic radiation. This energy is radiated by processes in the atomic structure of different materials and causes a wide range of effects.
the eye is sensitive is just a very narrow band in the total spectrum of electromagnetic emissions Electromagnetic waves
The transmission of light energy can be described as a wave motion or as ‘packets’ of energy called photons.
. All waves can change their direction when subject to the following effects. Visible radiation
The wavelengths of electromagnetic radiation that are visible to the eye range from approximately 380 to 760 nanometres ( 1 nanometre = 1/1000,000,00 metre) • White light is the effect on sight of combining all the visible wavelengths of light. The definition above is necessarily human-oriented and extra-terrestrial beings with scientific knowledge would not agree with it! • Monochromatic light is light of one particular wavelength and colour.
If the colours of the spectrum are recombined then white light is again produced. Varying the proportions of the individual colours can produce different qualities of ‘white’ light.
NATURE OF VISION
Vision is a sensation caused in the brain when light reaches the eye. The eye initially treats light in an optical manner, producing a physical image in the same way as a camera. This image is then interpreted by the brain in a manner which is psychological as well as physical.
The amount of light entering the lens is controlled by the iris, a coloured ring of tissue, which automatically expands and contracts with the amount of light present. The retina, on which the image is focused, contains light receptors which are concentrated in a central area called the fovea, and are deficient in another area called the blind spot.
A visual condition in which the observer feels either discomfort and/or exhibits a lower performance in visual tests (e.g. visual acuity or contrast sensitivity). This is produced by a relatively bright source of
light (called the glare source) within the visual field. A given bright light may or may not produce glare depending upon the location and intensity of the light source, the background luminance, the state of adaptation of the eye or the clarity of the media of the eye. direct glare Glare produced by a source of light situated in the same or nearly the same direction as the object of fixation. disability glare Glare which reduces visual performance without necessarily causing discomfort. discomfort glare Glare which produces discomfort without necessarily interfering with visual performance. eccentric glare See indirect glare. indirect glare Glare produced by an intense light source situated in a direction other than that of the object of fixation. Syn. eccentric glare. glare source See glare. glare tester An instrument for measuring the effect of glare on visual performance. There exist several (e.g. Brightness Acuity Tester (BAT), Miller-Nadler Glare Tester, Optec 1500 Glare Tester). Glare testing is valuable in patients with corneal and lenticular opacities before and after surgery and in elderly patients in whom adaptation to glare is usually more difficult. The Miller-Nadler Glare Tester consists of a glare source surrounding a Landolt C. The instrument contains 19 black Landolt C, all of the same size, 6/120 (or 20/400). Each Landolt C is presented in one of four orientations and from the highest to the lowest contrast at which the subject can no longer judge in which direction the letter appears. The contrast threshold is expressed in percentage disability glare.The Brightness Acuity Tester (BAT) is a standardized glare source of light. It is presented in a hemisphere held over one eye. The light source can subtend a visual angle of 8 to 70 degrees at a vertex distance of 12 mm. The patient is asked to read a visual acuity chart through a small aperture in the hemisphere. The chart can be a low-contrast or high-contrast log MAR visual acuity chart or, for example, the Pelli-Robson contrast sensitivity chart. veiling glare Glare caused by scattered light and producing a loss of contrast.
There are many different units for measuring light and it can get very complicated. Here are a few common measurement terms: Candela (cd) Unit of luminous intensity of a light source in a specific direction. Also called candle. Technically, the radiation intensity in a perpendicular direction of a surface of 1/600000 square metre of a black body at the temperature of solidification platinum under a pressure of 101,325 newtons per square metre. Footcandle (fc or ftc) Unit of light intensity, measured in lumens per square foot. The brightness of one candle at a distance of one foot. Approximately 10.7639 lux. Lumen (lm) Unit of light flow or luminous flux. The output of artificial lights can be measured in lumens.
Lux (lx) Unit of illumination equal to one lumen per square metre. The metric equivalent of foot-candles (one lux equals 0.0929 footcandles). Also called metre-candle.
Lighting for Elderly & Physically Challenged :
There are a few things to consider when installing lighting fixtures when considering a Physically Challenged person • Provide sufficient lighting, you can use frost tinted bulbs to reduce glare. fixture type can have the surface-mount, where the bulb is attached directly to the ceiling thus distributing the light evenly. Surface-mount fixtures should also be shielded to minimize glare.
• When installing switches, electrical outlets and other electrical controls, make sure that their locations inside the house is within easy reach for the disabled or handicapped person. Switches for electric light and power as well as door handles and other fixtures and fittings should be between 900 mm - 1200 mm from finished floor. Power point for general purpose should be fixed between 400-500 mm from the finished floor.
• Use natural lighting for windows whenever possible. You can try installing casement windows that are easy for a handicapped person to open and close. Choose simple window covering that will not stay in the way while the window is being operated.
• Install night lights on the bathroom. Use the highest wattage of bulbs allowed for your light fixtures. Plug-in some night lights that will automatically turn on when the room goes dark and always check them regularly . * Persons with limited vision may be able to discriminate between dark and brightshades and difference in primary colors. *Provision of illuminated signages, layout diagrams to help the persons easily reach the desired place.
Lifts :- Wherever lift is required as per bye-laws, provision of at least one lift shall
be made for the wheel chair user with the following cage dimensions of lift recommended for passenger lift of 13 persons capacity by Bureau of Indian Standards. Clear internal depth : llOOmm. Clear internal width : 2000 mm. Entrance door width : 900 mm. A hand rail not less than 600 mm. long at 800-1000 mm. above floor level shall be fixed adjacent to the control panel. The lift lobby shall be of an inside measurement of 1800 x 1800 mm. or more. The time of an automatically closing door should or minimum 5 seconds and the closing speed should not exceed 0.25 M/ Sec. The interior of the cage shall be provided with a device that audibly indicates the floor the cage has reached and indicates that the door of the cage for entrance/exit is either open or closed.
Optimal quality and quantity of lighting is emphasized. Quality of lighting may be expressed in terms of glare, brightness, color of light, direction and reflection, and other factors affecting visibility. Excessive brightness is discouraged as it is waste of energy and money and causes eye glare under prolonged exposure. Industrial standards usually call for the minimum requirement. Some of it can be applied to the standard for home lighting requirement.
Quality of Light ( Considerations )
Quality of lighting affects vision, especially in inspection work, fine manufacturing, color matching and in home activity such as prolong reading, writing, needle work etc. Below are some points to consider:
Glare - Avoid glares. Those stray bright lights directly or reflected from shiny surface should be minimized.
Relocate to an area without glare or reduce the number of lights. One example is to avoid placing the television in front of windows or with direct reflection of windows.
Contrast, distribution & reflection: Visual sharpness are affected by background. A uniformly
lighted surrounding will produce a higher level of comfort and efficiency of task. Generally, the brightness of task area should not be higher than the surrounding brightness by 3 times.
Flickers - Noticeable flickers from lighting tubes can raise discomfort and annoyance. Flickers at certain
rate can cause slow moving objects appears to be stationery. This may pose a safety hazard. Flickering light tubes should be changed promptly. The quantity of light is dependable on the task performed. Below is a summary of the brightness level required. With the use of the LITEcheck tester, the brightness level is easily measured in the unit of LUX.
CLASSIFICATION OF TASK
MINIMUM REQUIRED BRIGHTNESS (LUX)
CHARACTERISTICS OF THE ACTIVITY
Movement and orientation
Corridors walkways Cable tunnel Waiting room Store room Dining room Entrance hall Transaction counters Kitchen Children's playroom Office work Reading room Inspection of medium work Fine woodwork Drawing boards Most inspection tasks Proof reading Fine machine work Machine sewing Needle work
Visual tasks limited to movement and orientation
For coarse detail tasks where perception are not required
Moderately easy tasks
Moderately easy visual tasks with high contrasts or large details
Moderately difficult tasks
Areas where visual tasks with moderate details or with low contrasts.
Areas where visual tasks with small details or with low contrasts.
Very difficult tasks
Fine inspection Fine manufacture Areas where visual tasks with very small Paint retouching details or with low contrasts. Color matching of dyes
Extremely difficult tasks
Graphic arts inspection Hand tailoring Areas where visual tasks with extremely Inspection of dark small details or low contrasts. Visual aids goods may assist. Extra-fine bench work Fine fabric inspection Inspection of minute mechanisms Jewellery and watch making
Exceptionally difficult tasks
Areas where visual tasks with extremely small details or with very low contrasts. Visual aids may assist.
The above requirements are the minimum maintenance brightness. This means light bulbs should be cleaned or replaced if they fall below these standards.
MAINTENANCE OF LIGHTING :
1. Periodical checking the minimal required brightness throughout the life of light bulbs. Using the LITEcheck tester to check brightness of task area to determine if you need to shift the task area nearer to the light source or vice versa, or to perform maintenance. 2. Maintenance of light bulbs - All lighting bulbs or tube will degrade the moment you install them. Because our eyes are very adaptable to changing of light, using our eyes to judge lighting can be very misleading. Different type of lighting bulbs or tubes has varying life-span and they do not burn out immediately but degrade gradually.
Cleaning is the first step to improve brightness. Dust that accumulates on the surface of
bulbs, tubes or reflector can reduce brightness substantially. Caution: Remove bulbs or tubes from the fixture and wipe only with a damp cloths. Never clean directly with the bulbs or tubes attached to fixture. __________________________________________________________________________________