Illumination basic terms , law (प्रदीपन मूलभूत संज्ञा, कायदा) रोशनी की बुनियादी शर्तें, कानून in english

Electrician - Illumination
Illumination terms - Laws

Objective: After the end of this lesson you shall be able to

• explain the nature of light

• state principles and definitions used in illumination

• state properties and advantages of good illumination

• state and explain laws of illumination.

The nature of light

Light is a form of electromagnetic radiation. It is basically the same thing as the radio radiation used in radio, television, X-rays, gamma rays etc. Visible light is the radiation in that part of the spectrum between 380 and 780 nanometres(nm). Though light may also be beyond the limit, As nanometre (nm) is a wavelength of one millionth (10⁻⁹m) of a millimetre.

Within these limits, differences in the wavelengths produce the effect of colour, longer light being at the short-wave end and red at the long-wave end of the visible spectrum. Because the human eye is more sensitive to the yellow and green light in the middle of the spectrum, more power must be expended to produce the same effect from colours at the end of the spectrum.

Standard safety norms:
Trainees may be instructed to refer the International Electrotechnic Commission (IEC - 60050 part 845) site also for standard safety norms related with electrical illumination systems in the profession.

Few principle terms in connection with illumination are defined as follows:

Luminous flux (F): One of the kinds of light is termed as luminous flux is the energy radiated per second in the form of light by the luminous body. The unit of luminous flux is Lumen (lm). One lumen is defined as the luminous flux emitted in unit solid angle by a point source having a uniform intensity of one candela.

Luminous intensity (I): The luminous intensity of a source of light in a particular direction is defined as the luminous flux emitted by the source per unit solid angle in that direction. Its unit is candela (cd). 1 candela = 0.98 international candela.

Lumen (lm): It is the unit of luminous flux. This is defined as the amount of light emitted per second in a unit solid angle of one steradian from a source of one candela.

The shaded area A of a cone of one steradian is equal to the square of the radius. So the light emitting in this area is equal to one lumen.

The unit of light:
The unit of light (Illuminance) is expressed in lumen per square metre (lux).

Luminous intensity (Illuminance) is expressed in lumen per square metre (lux).
If a luminous flux of one lumen falls on a surface area of one square metre, the illumination is one lux.

This unit of illumination is derived from a standard candle. The unit is known as metre candle or lux.
One lux = one lumen/m²
Illumination at a point is defined as the luminous flux received per unit area. The luminous intensity is one candela and the source is placed at a height of 1 metre from the surface.

The flux of one lumen is falling on an area of one square metre. So the illumination is one lux.

Nature of work: Considering the nature of work, sufficient and suitable lightingwould be maintained. For example, a delicate work like radio and TV assembling, etc. requires good illumination to increase the production of work where as for rough work like storage, garages, etc needs very small illumination.

Design of Apartment: The design of apartment must be kept inmind while planning scheme for illumination. It means that the light emitted by the illumination source should not strike the eyes of the occupants or workers.

Cost: It is an important factor which should be considered while designing an illumination scheme for particular purpose.

Maintenance Factor: While planning illumination, it should also be kept in viewthat amount of useful light due to accumulation of dust or smoke on the source of light and after how much period cleanliness is required. Where there is a possibility of heavy loss of light due to the adherence of smoke, arrangement for the extra light is to be made from the very beginning.

Properties of good illumination

An illumination source should, have the following properties

i. It should have sufficient light.

ii. It should not strike the eyes.

iii. It should not produce glareness in the eyes.

iv. It7 should be installed at such a place that it gives uniform light.

v. It should be of correct type as needed.

vi. It should have suitable shades and8 reflectors.

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Advantages of good illumination

i. It increases production in the workshop.

ii. It reduces the chances of accidents.

iii. It does not strain the eyes.

iv. It reduces the wastage or loss of material.

v. It increases the interior decoration of the building.

vi. It gives smoothing effect to mind.9

Laws of illumination

Inverse Square law: If the internal radius of a sphere is increased from 1 metre to r metres, the surface area of it increased from 4S to 4Sr 2 metre^2. With a certain point source of light of one candela at the centre, the number of lumen, per square metre on the sphere of radius r metres.

$$\frac{4\pi }{4\pi r^2}=\frac{1}{r^2}$$

Explanation:

• The numerator is $4\pi$

• The denominator is $4\pi r^2$

• The $4\pi$ terms cancel out, leaving:

$$\frac{1}{r^2}$$

This kind of expression is common in physics, especially in contexts like gravitational or electric field equations where inverse square laws are involved.

Hence the illumination of a surface is inversely proportional to the square of its distance from the source. This is called the Inverse Square Law of Illumination.¹²

Lambert's cosine law: According to this law, illumination (E) is directly proportional to the cosine of the angle made by the normal to the surface upon which the direction of the incident flux. (Fig 3) Let $\varphi$ be the flux incident on the surface of area ABCD when in position 1. When this surface is so placed that the angle between the incident ray and the perpendicular to the surface EFGH is $\theta$. The luminous flux falling on area EFGH is $\varphi$.

Hence the illumination on the surface in position 1 is

$$E_1=\frac{\varphi }{\text{Area ABCD}}$$

But in position 2, the illumination is

$$E_2=\frac{\varphi }{\text{Area EFGH}}$$

(Area ABCD = AB x BC,

Area EFGH = EF x GF)