BOC Lighting Systems Efficiency Assessment Exam
Practice Questions And Correct Answers (Verified
Answers) Plus Rationales 2026 Q&A | Instant
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SECTION 1: LIGHTING FUNDAMENTALS & METRICS
Question 1
What is the definition of illuminance?
A) The total amount of light emitted by a source
B) The amount of light falling on a surface per unit area
C) The amount of light reflected from a surface
D) The efficiency of a lamp in converting electricity to light
Answer: B — The amount of light falling on a surface per unit area
Rationale: Illuminance is the measure of how much luminous flux falls on a
surface, measured in lux (lumens per square meter) or foot-candles. It depends on
the distance from the light source and the angle of incidence .
Question 2
What is the unit of illuminance?
A) Lumens
B) Watts
C) Lux
D) Candela
Answer: C — Lux
,Rationale: Lux is the SI unit of illuminance, defined as one lumen per square meter
(lm/m²). Foot-candles are used in imperial units .
Question 3
Which of the following formulas correctly expresses the inverse-square law for
illuminance?
A) E = I × r²
B) E = I / r²
C) E = r² / I
D) E = I × cosθ
Answer: B — E = I / r²
Rationale: The inverse-square law states that illuminance (E) is inversely
proportional to the square of the distance (r) from the point source. This means
when distance doubles, illuminance drops to one-quarter .
Question 4
When light strikes a surface at an angle, the illuminance is determined by which
law?
A) Inverse-square law only
B) Lambert's cosine law
C) Ohm's law
D) Boyle's law
Answer: B — Lambert's cosine law
Rationale: Lambert's cosine law states that illuminance on a surface is
proportional to the cosine of the angle between the incident light direction and the
surface normal. The formula is E = E₀ × cosθ .
,Question 5
The term "luminous efficacy" is defined as:
A) The ratio of electrical power input to light output
B) The ratio of luminous flux to electrical power input
C) The ratio of illuminance to power density
D) The percentage of energy converted to heat
Answer: B — The ratio of luminous flux to electrical power input
Rationale: Luminous efficacy is measured in lumens per watt (lm/W) and indicates
how efficiently a lamp converts electrical energy into visible light. Higher efficacy
means more light per unit of power .
Question 6
What is the typical luminous efficacy range for a modern fluorescent lamp?
A) 5-10 lumens/watt
B) 15-20 lumens/watt
C) 30-40 lumens/watt
D) 60-65 lumens/watt
Answer: D — 60-65 lumens/watt
Rationale: Fluorescent lamps typically have efficacies of 60-65 lumens/watt. This is
significantly higher than incandescent lamps (~10-15 lm/W) but lower than many
LED options .
Question 7
What is the installed load efficacy ratio (ILER) used to assess?
A) The total cost of a lighting system
B) The efficiency of a general lighting installation
C) The color rendering quality of lamps
D) The maintenance schedule for fixtures
, Answer: B — The efficiency of a general lighting installation
Rationale: ILER is a performance indicator that compares the actual installed load
efficacy (lux/W/m²) to a target value for the application and room index. It helps
identify opportunities for improvement .
Question 8
How is ILER calculated?
A) ILER = Target Lux/W/m² ÷ Actual Lux/W/m²
B) ILER = Actual Lux/W/m² ÷ Target Lux/W/m²
C) ILER = Total Watts ÷ Floor Area
D) ILER = Luminous Flux ÷ Input Power
Answer: B — ILER = Actual Lux/W/m² ÷ Target Lux/W/m²
Rationale: The formula is: ILER = Actual Lux/W/m² ÷ Target Lux/W/m². An ILER of
0.75 or above is considered satisfactory; 0.51-0.74 merits investigation; 0.5 or less
requires urgent action .
Question 9
What ILER value indicates that urgent action is required to improve lighting system
efficiency?
A) 0.75 or above
B) 0.51 to 0.74
C) 0.5 or less
D) 1.0 or above
Answer: C — 0.5 or less
Rationale: ILER ratios of 0.5 or less justify close inspection to identify options for
converting the installation to more efficient lighting equipment .
Practice Questions And Correct Answers (Verified
Answers) Plus Rationales 2026 Q&A | Instant
Download Pdf
SECTION 1: LIGHTING FUNDAMENTALS & METRICS
Question 1
What is the definition of illuminance?
A) The total amount of light emitted by a source
B) The amount of light falling on a surface per unit area
C) The amount of light reflected from a surface
D) The efficiency of a lamp in converting electricity to light
Answer: B — The amount of light falling on a surface per unit area
Rationale: Illuminance is the measure of how much luminous flux falls on a
surface, measured in lux (lumens per square meter) or foot-candles. It depends on
the distance from the light source and the angle of incidence .
Question 2
What is the unit of illuminance?
A) Lumens
B) Watts
C) Lux
D) Candela
Answer: C — Lux
,Rationale: Lux is the SI unit of illuminance, defined as one lumen per square meter
(lm/m²). Foot-candles are used in imperial units .
Question 3
Which of the following formulas correctly expresses the inverse-square law for
illuminance?
A) E = I × r²
B) E = I / r²
C) E = r² / I
D) E = I × cosθ
Answer: B — E = I / r²
Rationale: The inverse-square law states that illuminance (E) is inversely
proportional to the square of the distance (r) from the point source. This means
when distance doubles, illuminance drops to one-quarter .
Question 4
When light strikes a surface at an angle, the illuminance is determined by which
law?
A) Inverse-square law only
B) Lambert's cosine law
C) Ohm's law
D) Boyle's law
Answer: B — Lambert's cosine law
Rationale: Lambert's cosine law states that illuminance on a surface is
proportional to the cosine of the angle between the incident light direction and the
surface normal. The formula is E = E₀ × cosθ .
,Question 5
The term "luminous efficacy" is defined as:
A) The ratio of electrical power input to light output
B) The ratio of luminous flux to electrical power input
C) The ratio of illuminance to power density
D) The percentage of energy converted to heat
Answer: B — The ratio of luminous flux to electrical power input
Rationale: Luminous efficacy is measured in lumens per watt (lm/W) and indicates
how efficiently a lamp converts electrical energy into visible light. Higher efficacy
means more light per unit of power .
Question 6
What is the typical luminous efficacy range for a modern fluorescent lamp?
A) 5-10 lumens/watt
B) 15-20 lumens/watt
C) 30-40 lumens/watt
D) 60-65 lumens/watt
Answer: D — 60-65 lumens/watt
Rationale: Fluorescent lamps typically have efficacies of 60-65 lumens/watt. This is
significantly higher than incandescent lamps (~10-15 lm/W) but lower than many
LED options .
Question 7
What is the installed load efficacy ratio (ILER) used to assess?
A) The total cost of a lighting system
B) The efficiency of a general lighting installation
C) The color rendering quality of lamps
D) The maintenance schedule for fixtures
, Answer: B — The efficiency of a general lighting installation
Rationale: ILER is a performance indicator that compares the actual installed load
efficacy (lux/W/m²) to a target value for the application and room index. It helps
identify opportunities for improvement .
Question 8
How is ILER calculated?
A) ILER = Target Lux/W/m² ÷ Actual Lux/W/m²
B) ILER = Actual Lux/W/m² ÷ Target Lux/W/m²
C) ILER = Total Watts ÷ Floor Area
D) ILER = Luminous Flux ÷ Input Power
Answer: B — ILER = Actual Lux/W/m² ÷ Target Lux/W/m²
Rationale: The formula is: ILER = Actual Lux/W/m² ÷ Target Lux/W/m². An ILER of
0.75 or above is considered satisfactory; 0.51-0.74 merits investigation; 0.5 or less
requires urgent action .
Question 9
What ILER value indicates that urgent action is required to improve lighting system
efficiency?
A) 0.75 or above
B) 0.51 to 0.74
C) 0.5 or less
D) 1.0 or above
Answer: C — 0.5 or less
Rationale: ILER ratios of 0.5 or less justify close inspection to identify options for
converting the installation to more efficient lighting equipment .
