Light and Illumination MCQ Quiz - Objective Question with Answer for Light and Illumination - Download Free PDF

Mean spherical candle power (MSCP)

It is defined as the mean of the candle powers in all directions and in all planes from the source of light.

The total luminous flux reaching the working plane is given by:

Working Lumens = \({ϕ\times Utilization \space factor\over Utilization \space factor}\)

The illumination on the working plane is given by:

\(E={Lumens\over Total \space Area}\)

Calculation

The area of the room (A) = 10 × 4 = 40 m²

The total luminous flux emitted by ten lamps is:

ϕ = 10 × 150 × 4π =  18, 849.5 lumens

Working Lumens = \({18849.5\times 0.5\over 0.8}=11780.97\space lumens\)

The illumination on the working plane is:

\(E={11780.97\over 40}=294.52\space lux\)

• Illuminance - It is the measurement of the amount of light falling on a defined surface area.
• The formula is the luminous flux per unit area.
• Luminous Flux - It is the measurement of the total amount of visible light emitted by a light source.
• Lumen is the SI unit of luminous flux.
• Watt is the unit of Power and Joule is the unit of work or energy.

• The bimetallic strip is used by the thermostat of many devices like electric iron.
• The bimetallic strip is made up of two different types of metals (brass and iron) with a different coefficient of expansion bonded together.
• Hence in the presence of heat, the bimetallic strip expands differently. The metallic strip is connected to a contact spring through small pins. So that the temperature setting for a bi-metallic strip can be changed by moving it close and away from a heating element
• The bimetallic strip remains in physical contact with a contact point at a moderate temperature. However, at a temperature of the iron above a certain limit, the strip tends to bend towards the metal with a lower coefficient of expansion. At this point, the strip stops to be physically connected to the contact point and current stops flowing because of an opening of the circuit.
• Position (a) is when the iron is at a normal temperature.
• Position (b) is when the iron becomes too hot.

Concept:

Discharge Lamps:

• In all discharge lamps, an electric current is passed through a gas or vapor which renders it luminous.
• The elements most commonly used in this process of producing light by gaseous conduction are neon, mercury, and sodium vapors.
• The colors (i.e. wavelength) of light produced depend on the nature of the gas or vapor.
• For example, the neon discharge yields orange-red light of nearly 6,500 A.U. which is very popular for advertising signs and other spectacular effects.
• The pressure used in neon tubes is usually from 3 to 20 mm of Hg.
• High-pressure mercury vapor lamps, Neon lamps, Sodium vapor lamps, etc are examples of discharge-type lamps.
• Mercury-vapour light is always bluish-green and deficient in red rays, whereas sodium vapor light is orange-yellow.
• The discharge lamps work on the discharge phenomenon i.e, the voltage needs to discharge the ion from one side of the electrode to another side due to this high voltage is needed to pass the ion than the current so the current will lag behind the voltage at the normal working time.
• Hence Discharge lamp working at a lagging power factor.
• Due to the addition of the Choke and Capacitor, it has a high initial cost.
• It required approximately 5 minutes for starting due to the ionization process phenomena.

Light Emitting Diode (LED) 

• LED stands for light-emitting diode.
• LED lighting products produce light up to 90% more efficiently than incandescent light bulbs.
• LED bulbs consume very less power compared to CFL, Incandescent bulbs.

The difference between CFL and LED are as follows-

Important Points

The correct answer is luminous objects.

• Objects that emit light on their own are called luminous objects.

Key Points

• The light emitted by luminous objects allows us to see things around us.
• Examples of luminous objects are tube light, the sun, a lit candle, a glowing bulb, etc.
• Illuminated objects also known as non-luminous objects are the objects that shine in the light of other objects.
• Illuminated objects are capable of reflecting light to our eyes. For Eg. Moon, Sky.
• An opaque object is one that does not allow light to pass through it. For Eg. Concrete, wood, and metal etc.

• The most useful measure of a light source's color characteristics is the colour rendering index (CRI).
• CRI is a measure of a light source's ability to show object colors "realistically" or "naturally" compared to a familiar reference source, either incandescent light or daylight.
• The color rendering index (CRI) is measured as a number between 0 and 100.
• At zero (0), all the colours look the same.
• A CRI of 100 shows the true colors of the object.
• Incandescent and halogen light sources have a CRI of 100.
• Typically, light sources with a CRI of 80 to 90 are regarded as good and those with a CRI of 90+ are excellent.
• Higher the CRI, the better the color rendering capacity.

The correct answer is option 2): Red

Concept:

• Sodium-vapour lamp, electric discharge lamp using ionized sodium, used for street lighting and other illumination.
• A low-pressure sodium vapour (LPS) lamp contains an inner discharge tube made of borosilicate glass that is fitted with metal electrodes and filled with neon and argon gas and a little metallic sodium
• When the lamp is first started, it emits a dim red to warm the sodium metal; within a few minutes as the sodium metal vaporizes, the emission becomes the common bright yellow.

• The visor of a halogen flood lamp is made of glass.
• The bulb material is either quartz (fused silica) or alumina-silicate glass.
• Quartz glass has the appropriate temperature resistance for the tungsten-halogen cycle, which produces bulb temperatures of up to 1,652°F (900°C).
• For lamps of low wattage up to about 120 watts, alumina-silicate glass can be used.
• Either glass comes in the form of cylindrical tubes that are pre-cut to the desired length or cut to length by the lamp manufacturer.

Tungsten is used to make filaments. This is because of the following properties:

• It has a very high melting point.
• It is a good conductor of heat and electricity.
• Due to high resistivity, it does not burn at room temperature and the bulb glows at high temperatures.
• It does not oxidize in presence of a vacuum.

Among the following options, a low-pressure hydrogen lamp is not used for interior lighting.

Types of lightning lamps:

1.) Low-pressure hydrogen lamp:

• A hydrogen discharge lamp has a glass lamp enclosure formed with radiation-emitting particles.
• A hydrogen lamp is used for wavelength calibration in the UV range as it radiates continuously in that range.
• The hydrogen lamp does not produce a continuous visible spectrum.

2.) Incandescent lamp:

• These types of lampwork on the principle of incandescence, which produces light by heat.
• When the electric current is passed through the thin metal filament, the filament is heated, glows, and produces light.

3.) Fluorescent lamp:

• A fluorescent lamp is a low-weight mercury vapor lamp that uses fluorescence to deliver visible light.
• An electric current in the gas excites mercury vapor, which produces short-wave ultraviolet light that then causes a phosphor coating on the inside of the lamp to glow.
• A fluorescent lamp converts electrical energy into useful light much more efficiently than an incandescent lamp.

4.) Metal halide lamp:

• A metal-halide lamp is an electrical lamp that produces light by an electric arc through a gaseous mixture of vaporized mercury and metal halides. 
• The metal-halide lamps have a high luminous efficacy of around 75–100 lumens per watt which is about twice that of mercury vapor lights and 3 to 5 times that of incandescent lights.

• An IP rating is also known as Ingress Protection or International Protection ratings which are defined to the international standard of EN 60529 (British BS EN 60529:1992).
• This standard is used to define the levels of sealing effectiveness of electrical enclosures against intrusion from foreign bodies such as tools, dirt, and moisture. 
• The minimum IP rating for a garden light is IPX3 (normally IP43), which protects against rain or spraying water at a 60° angle from vertical.
• The Ingress Protection Rating of an outdoor light housing IP65, as it indicates a dust-tight housing as well as resistance to jets of water.
• IP Rating Reference Chart

Sodium vapour lamp:

It is low intensity so that the length of the lamp should be more. In order to get the desired length, it is made of a U-shaped tube.

This long U-tube consists of a small amount of neon gas and metallic sodium.

At the time of start, the neon gas vaporizes and develops enough heat to vaporize metallic sodium in the U-shaped tube.

Initially, the sodium is in the form of a solid, deposited on the walls of the inner tube.

When enough voltage is impressed across the electrodes, the discharge starts in the inert gas; it operates as a low-pressure neon lamp with pink colour.

The temperature of the lamp increases gradually, and the metallic sodium vaporizes and then ionizes thereby producing monochromatic yellow.

Important:

Advantages:

• Good efficiency
• Colour rendering is better than that of high-pressure sodium street lights
• Some lamps last far longer than the 24000-hour mark, sometimes 40 years

Disadvantages:

• Like many lamps, it contains traces of mercury which must be disposed of properly
• Human skin looks green under the light, it is poor for colour film/photography
• The warm-up time required to start the lamp

Applications:

Large areas like parks, street lighting, high ceiling buildings, and gyms

The correct answer is option 3):(Lumen )

Concept:

• Luminous flux is the measure of the brightness of a light source in terms of energy being emitted.
• In other words, it is the measure of the perceived power of light.
• The S.I unit of Luminous Flux is Lumen.
• Lux is the unit of illuminance.
• Lamp efficiency is measured in lumen/watt
• Candela unit of luminous intensity