Illumination and Lighting Engineering MCQs 2026

Illuminance on a surface is measured in

1. A candela only ✓
2. B lumen ✓
3. C watt per steradian ✓
4. D lux (lx) ✓

Luminous flux is measured in

1. A lumen (lm) ✓
2. B lux only without area ✓
3. C candela-second only ✓
4. D watt ✓

One lumen is defined in relation to

1. A only IR radiation power ✓
2. B radiant flux weighted by the luminous efficiency function V(λ) ✓
3. C only magnetic flux in weber ✓
4. D only cable charging VAR ✓

Luminous intensity of a point source is measured in

1. A candela (cd) ✓
2. B lux ✓
3. C lumen per hour ✓
4. D ohm ✓

Power factor of magnetic-ballast fluorescent luminaire is often improved by

1. A removing capacitor entirely always ✓
2. B high power factor or electronic ballast ✓
3. C using only resistance ballast for unity PF ✓
4. D increasing THD without correction ✓

Starting voltage for fluorescent tube is highest at

1. A highest temperature always ✓
2. B zero humidity only condition ✓
3. C lowest ambient temperature ✓
4. D full lamp lumen output ✓

Metal halide lamps are preferred for

1. A only indicator pilot lamps ✓
2. B good color rendering and high efficacy in sports/factory lighting ✓
3. C only series street lighting without gear ✓
4. D only battery trickle charge ✓

Lamp life rating (e.g., 1000 h incandescent, 50000 h LED) indicates

1. A guaranteed illuminance lux level ✓
2. B maximum supply voltage ✓
3. C earth loop impedance ✓
4. D statistical median or rated hours to replacement criteria ✓

Cut-off luminaire in street lighting directs light

1. A only into the sky for astronomy ✓
2. B downward to the road with limited upward spill ✓
3. C only into adjacent property without control ✓
4. D only horizontally at eye level ✓

Mounting height of street lights affects

1. A only transformer tap position ✓
2. B only cable insulation thickness only ✓
3. C spacing, uniformity and glare on the roadway ✓
4. D only motor synchronous speed ✓

Average lux on road surface in street lighting design uses

1. A only Ohm law of conductor ✓
2. B only Ferranti effect formula ✓
3. C only welding heat input equation ✓
4. D lumen method with utilization factor and maintenance factor ✓

Semi-cut-off and non-cut-off street lanterns differ in

1. A amount of light allowed above horizontal (upward light) ✓
2. B only lamp wattage without optics ✓
3. C only pole material wood vs steel ✓
4. D only supply neutral earthing ✓

Spacing between street lights is increased when

1. A only when lamps are removed ✓
2. B mounting height and luminaire candela distribution allow ✓
3. C only when voltage is reduced 50% ✓
4. D only when power factor is zero ✓

LED street lighting retrofit often improves

1. A only THD without any lumen gain ✓
2. B only pole weight without optics ✓
3. C efficacy, life and controllability (dimming/scheduling) ✓
4. D only earth resistance of rod ✓

Pole setback and overhang influence

1. A only neutral current in 4-wire system ✓
2. B only rotor resistance of slip-ring motor ✓
3. C only Buchholz relay gas volume ✓
4. D light distribution on carriageway and footpath ✓

International practice for road lighting classes considers

1. A only conductor strand count ✓
2. B only fuse element alloy only ✓
3. C traffic volume, road type and pedestrian conflict areas ✓
4. D only synchronous condenser rating ✓

Series street lighting (historical) used

1. A parallel household wiring only ✓
2. B only DC traction feeder ✓
3. C constant current series circuit with isolation transformers ✓
4. D only open-delta transformer without lamps ✓

Light pollution from poor street lighting design is reduced by

1. A full cut-off optics and curfew dimming where permitted ✓
2. B aiming luminaires at sky ✓
3. C using only bare lamps on low poles ✓
4. D maximizing uplight for ambiance ✓

Design illuminance with MF less than unity means installed initial lux is

1. A lower than maintained always ✓
2. B equal to zero always ✓
3. C higher than the target maintained illuminance ✓
4. D independent of lamp choice ✓

LED lamp efficacy compared to incandescent is generally

1. A always lower than 10 lm/W ✓
2. B equal to candle only ✓
3. C independent of junction temperature ✓
4. D much higher (often 80–150+ lm/W) ✓

Tungsten halogen cycle in halogen lamps

1. A redeposits evaporated tungsten back on the filament ✓
2. B eliminates all heat from filament ✓
3. C replaces need for glass envelope ✓
4. D converts AC to DC ✓

High intensity discharge (HID) lamps include

1. A mercury vapor, metal halide and high-pressure sodium ✓
2. B only tungsten halogen without discharge ✓
3. C only neon sign electrodes without arc ✓
4. D only LED chip arrays ✓

Compact fluorescent lamp (CFL) advantage over incandescent is

1. A lower efficacy than incandescent ✓
2. B no need for any phosphor ✓
3. C higher luminous efficacy and longer life ✓
4. D operation without any ballast ever ✓

Fluorescent lamp requires ballast to

1. A increase filament resistance to infinity ✓
2. B convert AC to DC at load only ✓
3. C measure earth fault current ✓
4. D limit current and provide starting voltage ✓

Incandescent lamp light is produced by

1. A gas discharge in mercury vapor only ✓
2. B heating a tungsten filament to incandescence ✓
3. C LED junction electroluminescence ✓
4. D chemical combustion of fuel ✓

Spacing to height ratio (SHR) in interior lighting relates to

1. A short-circuit level of substation ✓
2. B uniformity of illuminance for a given luminaire distribution ✓
3. C transformer impedance only ✓
4. D welding electrode diameter only ✓

Color rendering index (CRI) degradation in aging lamps

1. A may be considered alongside lumen depreciation in critical areas ✓
2. B is unrelated to lighting maintenance ✓
3. C replaces illuminance calculation entirely ✓
4. D eliminates glare completely ✓

Emergency lighting levels are maintained considering

1. A appropriate MF and minimum lux codes for escape routes ✓
2. B only decorative color temperature ✓
3. C only highest HF ballast THD ✓
4. D only motor pull-out torque ✓

Luminous efficacy of a light source is

1. A watts per lumen always below 1 ✓
2. B lumens produced per watt of input power ✓
3. C candela per meter only ✓
4. D power factor of lamp only ✓

A 100 W incandescent lamp producing 1700 lm has efficacy about

1. A 17 lm/W ✓
2. B 100 lm/W ✓
3. C 1.7 lm/W ✓
4. D 170 lm/W ✓

Luminous flux required on a work plane depends on

1. A required illuminance and area (Φ = E × A) ✓
2. B only lamp voltage ✓
3. C only power factor of motor ✓
4. D only cable length ✓

Maintenance factor (MF) in lighting design accounts for

1. A only supply voltage rise ✓
2. B lamp lumen depreciation and dirt depreciation over maintenance period ✓
3. C only transformer iron loss ✓
4. D only motor slip ✓

Utilization factor (UF) in interior lighting depends on

1. A only conductor resistivity ✓
2. B only breaker making capacity ✓
3. C only grid frequency deviation ✓
4. D room geometry, reflectances and luminaire photometrics ✓

Glare in lighting installations is reduced by

1. A using only bare lamps at low height ✓
2. B maximizing direct glare toward eyes ✓
3. C eliminating all diffusers always ✓
4. D proper shielding, mounting height and limiting luminance of sources ✓

Lamp lumen depreciation (LLD) factor represents

1. A ratio of voltage to current ✓
2. B power factor of ballast only ✓
3. C ratio of lumens at end of life to initial lumens ✓
4. D cable derating factor ✓

Dirt depreciation factor (DDF) in lighting allows for

1. A increased lamp voltage only ✓
2. B motor starting current ✓
3. C transformer tap change ✓
4. D reduced light output due to dust on luminaires and room surfaces ✓

Combined maintenance factor MF is typically

1. A sum of LLD and DDF only ✓
2. B always equal to 2 ✓
3. C product of LLD and DDF (and other factors if used) ✓
4. D independent of cleaning schedule ✓

Relamping before average lamp life in group relamping

1. A always wastes all lamps instantly ✓
2. B eliminates need for MF ✓
3. C maintains more uniform illuminance than spot relamping alone ✓
4. D reduces efficacy to zero ✓

Cleaning luminaires on schedule improves

1. A only power factor of supply ✓
2. B only cable insulation resistance ✓
3. C only short-circuit MVA ✓
4. D effective lumens reaching the work plane ✓

For LED luminaires, lumen maintenance is often quoted as

1. A only peak candela at 1 ms ✓
2. B L70 or L80 life (hours to 70% or 80% initial lumens) ✓
3. C only THD of driver ✓
4. D only earth resistance ✓