100 Most Important MCQ Of Illumination with answer & explanation

Answer.4. Decoration purpose

Explanation:-

In a semi-indirect lighting scheme, about 60~90% of the light from the lamp is thrown upwards to the ceiling and the remaining luminous flux reaches the working surface. Glare will be completely eliminated with such type of lighting scheme. This scheme is widely preferred for indoor lighting decoration purposes.

Answer.4. 80 – 90%

Explanation:-

The direct lighting scheme is most widely used for interior lighting schemes. In this scheme, by using deep reflectors, it is possible to make 90% of light fall just below the lamp. This scheme is more efficient but it suffers from hard shadows and glare. Hence, while designing such schemes, all the possibilities that will cause glare on the eye have to be eliminated. It is mainly used for industrial and general outdoor lighting.

Answer.1. 4π

Explanation:-

A solid Angle is a cone that an object subtends at a point in space. It is a measure of how big an object appears to an observer looking from the said point in space. For example, a small object, which is nearer to the observer could subtend the same solid angle as a large object which is far away from the observer. The solid angle is proportional to the surface area of a projection of that object onto a sphere centered at the point where the observer lies, divided by the square of the radius, R of the sphere.

or

The solid angle is the angle subtended at a point in space by an area, i.e., the angle enclosed in the volume conned by numerous lines Iying on the surface and meeting at the point. it is usually denoted by symbol ω’ and is measured in steradian.

Solid angle ω = area/r² steradian

The largest solid angle subtended at the center of the sphere

ω = Area of sphere/r²

ω = 4πR²/R²

ω = 4π steradian

Answer.1. For improving the power factor of the circuit

Explanation:-

In order to start the sodium vapor lamp, 380-50 V of striking voltage is required for 40- and 100-W lamps. These voltages can be obtained from a high reactance transformer or an autotransformer. The operating power factor of the lamp is very poor so a capacitor is placed to improve the power factor to above 0.8.

Answer.1. Sodium vapor lamp

Explanation:-

A sodium-vapor lamp features well monochromaticity, high brightness, and good luminous efficiency. It is a gas-discharge lamp. The efficiency of the sodium-vapor lamp is related to the sodium-vapor pressure. Two peaks exist at the pressure of 0.5 and 10⁴ Pa. Low-pressure sodium lamp has higher efficiency and better monochromaticity than high-pressure sodium (HPS) lamp.

The luminous efficiency of a low-pressure sodium vapor lamp is about 200 lumen/watt.

Mercury Vapor lamp:- Mercury-vapour lamps were the first commercialized HID(High-Intensity Discharge) lamps, which use an electric arc through mercury vapor to produce light. It originally produced a bluish-green light, but more recent versions can produce clear white light. Compared to incandescent and most fluorescent lights, it is more energy efficient with luminous efficacies lying in the range of 35-65 lumens/watt and lifetime at about 24,000 h.

Neon Lamp:- This is a cold cathode lamp, in which no filament is used to heat the electrode for starting. It consists of two electrodes placed at the two ends of a long discharge tube.

The discharge tube is filled with neon gas. A low voltage of 150 V on DC or 110 V on AC is impressed across the two electrodes; the discharge takes place through the neon gas that emits light or electromagnetic radiation reddish in color. The neon lamp electric circuit consists of a transformer with high leakage reactance in order to stabilize the arc. The capacitor is used to improve the power factor. Neon lamp efficiency is approximately 15-40 lumens/W. The power consumption of the neon lamp is 5 W.

Answer.2. Startless fluorescent lamp

Explanation:-

A fluorescent lamp without a starter is commercially called ‘quick start’ or ‘instant start’ fluorescent lamp. This lamp does not need a starter.

In the present day, these startless lamps are used for rapid or instant start. In this type of lamp, the filament transformer replaces the starter. The two electrodes are heated with the help of secondary of this transformer. This preheating and the presence of full supply voltage across the electrodes cause the ionization of the medium.

Answer.4. GLS

Explanation:-

GLS lamps produce light as a result of the heating effect of an electrical current. Most of the electricity goes to producing heat and a little to producing light. A fine tungsten wire is first coiled and coiled again to form the incandescent filament of the GLS lamp. GLS lamp is considered as a resistive load. So the power factor of it is 1(unity).

Answer.1. 0.228

Explanation:-

The active Power in an A.C circuit is defined as

P = V.I.Cosφ

Where

P is Power =20 W

V = Voltage = 220 V

I = Current = 0.4 A

20 = 220 × 10 × Cosφ

Cosφ = 0.22

Answer.2. 110 – 120 Volts

Explanation:-

Neon Lamp:- This is a cold cathode lamp, in which no filament is used to heat the electrode for starting. It consists of two electrodes placed at the two ends of a long discharge tube.

The discharge tube is filled with neon gas. A low voltage of 150 V on DC or 110 V on AC is impressed across the two electrodes; the discharge takes place through the neon gas that emits light or electromagnetic radiation reddish in color. The sizes of electrodes used are equal for both AC and DC supplies. On DC, neon glow appears nearer to the negative electrode; therefore, the negative electrode is made larger in size. The neon lamp electric circuit consists of a transformer with high leakage reactance in order to stabilize the arc. The capacitor is used to improve the power factor. Neon lamp efficiency is approximately 15-40 lumens/W. The power consumption of the neon lamp is 5 W.

If the helium gas is used instead of neon, pinkish-white light is obtained. These lamps are used as night lamps and as indicator lamps and used for the determination of the polarity of DC mains and for advertising purposes.

Answer.3. Both 1 and 2

Explanation:-

A black object, such as a piece of lava rock, absorbs most of the light intensity when illuminated by white light. A very small amount of light is scattered, and from that small amount, we can tell the shape and size of the rock. All colors in white light (red, green, and blue) are absorbed equally by the black rock, and a small proportion of each one, in equal amounts, is scattered.

A white piece of paper or a snowball behaves in a very similar way: AH colors are equally reflected. The difference is that in this case, no light is absorbed. All the illuminating light is scattered. The blue, green, and red components are reflected in equal amounts, our eyes see the high brightness, and both the paper and the snowball appear white.

All colored objects absorb certain wavelengths and scatter others. The apple appears red because, when illuminated by white light, it absorbs green and blue and scatters red light only.

A lemon appears yellow because it absorbs blue light and scatters red and green light. Our eyes perceive these red and green wavelengths, we add them together and interpret the lemon’s color as yellow.