100 Most Important MCQ Of Illumination with answer & explanation

Answer.4. Nitrogen

Explanation:-

Argon and nitrogen are the gases most commonly used in filament bulbs. Nitrogen will minimize the risk of arcing but will absorb more heat than argon.

Argon is used by itself in general service lamps. A mixture of the two gases is used in incandescent lamps where the tendency for arcing is more likely, such as in projector lamps.

In this case, the amount of nitrogen present is kept very small as little as 5% in order to obtain optimum lamp efficiency. Lamps filled with krypton gas have a longer life than argon and nitrogen lamps and cost more.

Answer.3. 1/cos³θ

Explanation:-

Lambert’s Cosine Law

Lambert’s Cosine Law states that when light falls obliquely on a surface, the illumination of the surface is directly proportional to the cosine of the angle θ between the direction of the incident light and the surface normal. The law is also known as the cosine emission law or Lambert’s emission law.

Illumination (E) = I.Cos³θ/r²

Where

I = luminous Intensity

r = radius

Answer.3. Current limiting device

Explanation:-

There are mainly two functions of the choke coil

1.  Limit the current.
2. Produce high voltage across tube light.

Choke must provide a suitable striking (ignition) voltage across the bulb at starting such that an electric arc can sustain between the electrodes afterward. Secondly, the ballast is responsible for limiting the current flow across the lamp during its normal operation of it. 

As the initial impedance is high, the striking voltage required to ignite the arc would also be higher than the normal operating voltage (around 300% higher) of a fluorescent lamp. Immediately after the lamp is struck, the impedance drops to its minimum value, representing negative resistance characteristics that need some form of current limiting to prevent lamp destruction from excessive current.

Limit the current

• In a gas discharge, such as a fluorescent lamp, current causes resistance to decrease. This is because as more electrons and ions flow through a particular area, they bump into more atoms, which frees up electrons, creating more charged particles.
• In this way, the current will climb on its own in a gas discharge, as long as there is adequate voltage (and household AC current has a lot of voltage).
• If the current in a fluorescent light isn’t controlled, it can blow out the various electrical components.

Produces High voltage Across Tubelight

• Choke is nothing but the coil/ballast ( inductor) which is used to induce the high voltage across it. as we know that inductor has the property to induce high voltage for a brief period of time, this high voltage is required to ionize the gases in the starter.

Answer.2. a-(iv), b-(i), c-(ii), d-(iii)

Explanation:-

(a)The SI unit of luminous flux is the lumen (lm).

(b) The SI unit of luminous intensity is the candela (cd)

(c) Lumen is defined as the luminous flux emitted by a source of one candlepower per unit solid angle in all directions.

Lumen = Candle power × intensity Solid angle

(d) The CP of a source is defined as the total luminous flux lines emitted by that source in a unit solid angle.

CP = Lumen/ω

Answer.2. Resistance

Explanation:-

Fluorescent lamps can run directly from a d.c. supply of sufficient voltage to strike an arc. A choke has very low impedance with dc. supply. Hence, resistance in series with the choke must be used.

This would consume about as much power as the lamp. When operated from d.c. supply, the starting switch is often arranged to reverse the polarity of the supply to the lamp each time it is started; otherwise, the mercury accumulates at one end of the tube. Fluorescent lamps are (almost) never operated directly from d. c. supply for those reasons.

 The choke is connected in series with the tube filament or resistance which provides a voltage impulse for starting the lamp and acts as ballast during running i.e it drops the voltage and smoothens the current.

Answer.1. Rate of energy radiation in the form of light waves

Explanation:-

Luminous flux is defined as the rate of energy radiation in the form of light waves. It is denoted by φ and its SI unit is Lumen.

Answer.1. Fluorescent lamp

Explanation:-

Fluorescent lamps operate on the principle of gaseous discharge. They rely on the production of ultraviolet light from the ionization of mercury to charge fluorescent materials which absorb the UV rays and transform them into longer wavelengths in the range of visible light. The color of the light and the efficacy of the lamp are affected by the selection of the phosphor compound.

More than half of the input energy used by fluorescent lamps is used to produce UV light. Yet, due to the fluorescent of the phosphor compounds, the distribution of energy output is modified; less than 20 percent UV, up to 37 percent IR, about 20-30% percent heat radiation at less than 5 percent visible light.

All light sources produce heat and every unit of electrical energy put into an interior lighting system appears as heat. For corresponding values of installed flux, the high efficacies of fluorescent lamps mean, in comparison with tungsten filament lamps, that a lower wattage is required and therefore less heat is produced.

Most of the energy from tungsten filament lamps appears as radiation about 80-90%, while the proportion of radiation from fluorescent lamps is much smaller and most of the heat is removed by conduction and convection.

Answer.4. Carbon Arc lamp

Explanation:-

Arc lamps are also used to produce very intense UV radiation for e.g.  Mercury arc lamp, carbon arc lamp, either a medium wave or long wave. The cored carbon arc is probably the best-known lamp of this type. An arc is produced by passing electricity as a large spark across two electrodes of carbon in dose proximity. Although this arc lamp emits some long-wave UV radiation, its primary use is in visual-light photography and photomicrography. A continuous spectrum is produced in the UV, visible, and IR spectral ranges. 

The carbon Arc lamp is continuous and a genuine sunlike radiator, with the exception that this lamp gives shorter ultraviolet rays than the sun. 

The carbon arc lamp produces its light when high amperage direct current is applied to one or two carbon rods or electrodes within the lamp housing. A stream of electrons in the current forms a brilliant arc as it jumps a narrow gap between the two carbon rods. As the lamp burns, the feed rod oxidizes and must be continually adjusted (or trimmed).

There is no lamp that can better simulate the intense light of the sun or the hard light of the moon but it almost produces nearly ultraviolet light. The correlated color temperature of a white flame, carbon arc lamp is 5800°K, which closely matches photographic daylight.

Answer.4. 20%

Explanation:-

Fluorescent tubes:

The traditional tubular fluorescent lamp consists of a sealed gas-filled glass tube with a phosphor-coated inner surface. When switched on, the mercury vapor within the tube ionizes, causing the phosphor coating to glow brightly (fluoresce); the color depends on the specific materials used. The fluorescent lamp is three to four times more efficient than a tungsten source (more light per watt), so power consumption is correspondingly lower for the same light intensity. There is little radiant heat in the light beam. (Half of the power used by tungsten light sources may be wasted as heat! ) Because fluorescent lights provide a broad light source, the illumination is relatively soft and easier on the eyes than intense spotlights. Fluorescent tubes have a relatively long life.

Fluorescent lamps operate on the principle of gaseous discharge. They rely on the production of ultraviolet light from the ionization of mercury to charge fluorescent materials which absorb the UV rays and transform them into longer wavelengths in the range of visible light. The color of the light and the efficacy of the lamp are affected by the selection of the phosphor compound.

More than half of the input energy used by fluorescent lamps is used to produce UV light. Yet, due to the fluorescent of the phosphor compounds, the distribution of energy output is modified; less than 20 percent UV, up to 37 percent IR, about 20-30% percent heat radiation at less than 5 percent visible light.

All light sources produce heat and every unit of electrical energy put into an interior lighting system appears as heat. For corresponding values of installed flux, the high efficacies of fluorescent lamps mean, in comparison with tungsten filament lamps, that a lower wattage is required and therefore less heat is produced.

Most of the energy from tungsten filament lamps appears as radiation about 80-90%, while the proportion of radiation from fluorescent lamps is much smaller and most of the heat is removed by conduction and convection.

The first advantage of tubular fluorescent lamps is their high efficacy. The 100W coiled-coil tungsten lamp gives about 1260 lm (12.6 Im/W), whereas a fluorescent tube such as the 65 W warm white has a lighting design output of 4600 Im. The control gear of else fluorescent lamp consumes about 15 W so the total efficacy is about 57 Im/W, which is more than four times per watt of the light output of the 100 W tungsten lamp.

Answer.3. Radiation

Explanation:-

Heat transfers from hotter objects to cooler objects and never in the opposite direction. When you pour coffee into a standard ceramic mug, for example, you can see heat transfer to the air as steam rises from the mug. If you hold the mug, you can feel that heat has been transferred from the coffee to the mug and now into your hands. Heat transfers in three ways:

Conduction: Heat transfer between particles (for example, the coffee and the mug) without the displacement of the particles themselves. Conduction occurs when heat is transferred from one solid to another, as in the case of heat traveling through a mug and into your hands.

Convection: Heat transfer through the movement of particles as hotter, lighter particles rise and displace cooler, heavier particles. Convection enables a space heater to heat an entire room, as hot air continuously rises from the heater, displacing the cooler air until all the air in the room reaches a certain temperature.

Radiation: Heat transfer through electromagnetic waves. Radiation is how the sun transfers energy to the Earth. You also feel radiant heat when you’re near a fire. A unique property of radiant heat is that it requires no medium to carry it, so it can travel through a vacuum, as radiant heat from the sun travels through the vacuum of space.

Since most of the energy from tungsten filament lamps appears as heat energy therefore the energy is transferred through radiation until or unless you touch the bulb with your hand.