Every Illumination question asked in GPSC DEE Electrical, GPSC AE Electrical, Supervisor Instructor — solve, check instantly, then read the formula and exam tip.
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D — Fluorescent lamp. Its long tube gives wide, diffuse, low-glare light with much better luminous efficacy than incandescent lamps.
View answer & solutionD — Halogen lamp. It is an improved incandescent source with a halogen regenerative cycle, giving high filament temperature, stable output, ~3200 K colour temperature and CRI close to 100.
View answer & solutionC — Lux. Illuminance is luminous flux falling per unit area: 1 lux = 1 lumen/m².
View answer & solutionModern industrial LEDs provide high luminous efficacy and long service life compared with older mercury-vapor technology. Suitable luminaires can also provide high CRI, so poor color rendering is not an inherent LED limitation; inspection areas can be designed with high-CRI LED sources. Key relation: Luminous efficacy=lumens/electrical watt.
Exam focus: Check efficacy, lifetime, CRI and glare together. Common trap: LED does not automatically mean poor CRI.
View answer & solutionA luminaire is the complete lighting unit/fixture: it includes the lamp or LED light source together with housing, optical components, electrical gear/driver and parts needed to distribute, position and protect the light source.
View answer & solutionA — Bluish-white. Mercury emission lines are mainly in the blue-green-violet region with almost no red, so the light appears bluish-white.
View answer & solutionThe luminaire is 4 ft below a 16-ft ceiling and the work plane is 4 ft above the floor, so cavity height is 8 ft. Room cavity ratio is RCR=5h(L+W)/(LW). Substituting h=8 ft, L=120 ft and W=60 ft gives RCR=1.0, matching option B.
View answer & solutionB — Thermal insulation. The evacuated outer envelope keeps the discharge tube hot enough to vaporise sodium and protects the inner tube; it is not the light source.
View answer & solutionLED luminaires are the dominant high-efficiency choice for new street-lighting projects because they provide high luminous efficacy, long life, controllability, good optical directionality and lower maintenance compared with legacy discharge lamps.
