1. What is the SI unit of luminous flux?
A. Lux
B. Candela
C. Lumen ✅
D. Watt
📝 Explanation: Lumen (lm) is the SI unit of luminous flux, which measures the total quantity of visible light emitted by a source.
2. Which law states that illumination is inversely proportional to the square of the distance from the light source?
A. Lambert’s Cosine Law
B. Inverse Square Law ✅
C. Planck’s Law
D. Stefan-Boltzmann Law
📝 Explanation: The Inverse Square Law states that illumination decreases proportionally to the square of the distance from the source.
3. Which lamp has the highest luminous efficacy?
A. Incandescent lamp
B. Fluorescent lamp
C. LED lamp ✅
D. Mercury vapor lamp
📝 Explanation: LED lamps are most efficient, converting more electrical energy into light with very little heat loss.
4. What is the unit of illuminance?
A. Lumen
B. Candela
C. Lux ✅
D. Watt
📝 Explanation: Illuminance is measured in lux, which is lumens per square meter (lm/m²).
5. Which of the following lamps is most suitable for street lighting?
A. Incandescent lamp
B. Fluorescent lamp
C. Sodium vapor lamp ✅
D. Mercury vapor lamp
📝 Explanation: Sodium vapor lamps offer high efficacy and better penetration through fog, ideal for streets.
6. The ratio of luminous flux emitted by a source to the power consumed is called:
A. Luminous intensity
B. Luminous efficacy ✅
C. Illuminance
D. Luminance
📝 Explanation: Luminous efficacy = lumens/watt, showing how efficiently a light source converts power into light.
7. Which factor affects the depreciation of illumination over time?
A. Lamp lumen depreciation
B. Room surface dirt accumulation
C. Lamp aging
D. All of the above ✅
📝 Explanation: All listed factors contribute to reduced illumination over time.
8. Which of the following is a disadvantage of fluorescent lamps?
A. High luminous efficacy
B. Long life
C. Contains mercury ✅
D. Low heat generation
📝 Explanation: Fluorescent lamps contain harmful mercury, making disposal and handling difficult.
9. In a lighting scheme, the ratio of the minimum to average illumination is called:
A. Uniformity ratio ✅
B. Utilization factor
C. Maintenance factor
D. Depreciation factor
📝 Explanation: The uniformity ratio ensures even lighting across an area for comfort and safety.
10. Which of the following is used to measure illumination?
A. Lux meter ✅
B. Photometer
C. Lumen meter
D. Candela meter
📝 Explanation: Lux meters directly measure the illuminance level in lux.
11. Which lamp has the best color rendering index (CRI)?
A. Incandescent lamp ✅
B. Fluorescent lamp
C. Sodium vapor lamp
D. Mercury vapor lamp
📝 Explanation: Incandescent lamps have a CRI close to 100, rendering colors naturally.
12. The total luminous flux emitted by a source is measured in:
A. Candela
B. Lux
C. Lumen ✅
D. Watt
📝 Explanation: Lumen measures the total amount of visible light emitted by a source.
13. Which of the following is not a method of artificial lighting?
A. Direct lighting
B. Semi-direct lighting
C. Indirect lighting
D. Natural lighting ✅
📝 Explanation: Natural lighting comes from sunlight and is not an artificial lighting method.
14. The illumination at a point on a surface is directly proportional to:
A. Square of the distance from the source
B. Cosine of the angle between the normal and the direction of light ✅
C. Sine of the angle between the normal and the direction of light
D. Tangent of the angle between the normal and the direction of light
📝 Explanation: According to Lambert’s Cosine Law, illumination ∝ cos(θ).
15. Which lamp operates at the lowest temperature?
A. Incandescent lamp
B. Fluorescent lamp
C. LED lamp ✅
D. Halogen lamp
📝 Explanation: LEDs produce very little heat compared to other lamps, making them efficient and safe.
16. Which of the following factors does not affect the level of illumination?
A. Distance from the source
B. Angle of incidence
C. Color of the light ✅
D. Reflectance of the surface
📝 Explanation: The color of light doesn’t impact the intensity of illumination, only the visual perception.
17. The human eye is most sensitive to which color?
A. Red
B. Green ✅
C. Blue
D. Violet
📝 Explanation: The human eye is most sensitive to green light (around 555 nm wavelength).