CLC Light Source Technology & LEDs 3

Question 1

What is the primary cause of 'color shift' in LED luminaires over their rated life?

Accepted Answer

Phosphor degradation and silicone yellowing in the package

Answer

Phosphor degradation and silicone encapsulant yellowing caused by heat and UV exposure are the primary drivers of chromaticity shift in LED products over time.

Question 2

Which LED metric specifically describes the ratio of luminous flux emitted in the forward hemisphere versus total fixture input power?

Accepted Answer

Luminaire efficacy rating (LER)

Answer

LER (Luminaire Efficacy Rating) accounts for luminaire optical losses, driver losses, and thermal losses to express delivered lumens per input watt.

Question 3

A TRIAC (phase-cut) dimmer causes visible flicker with an LED driver primarily because:

Accepted Answer

The LED driver cannot regulate current smoothly from the chopped AC waveform

Answer

TRIAC dimmers chop the AC waveform; many LED drivers struggle to filter this irregular input and produce stable DC current, causing flicker or instability.

Question 4

What does 'R9' value indicate in a CRI report for an LED source?

Accepted Answer

The rendering of saturated red (test color sample 9)

Answer

R9 is the CRI score for test color sample 9, which is a saturated red; a high R9 (>50) is critical for applications like food retail or skin tones.

Question 5

Which thermal parameter is used to compare the heat dissipation capability of different LED packages from junction to the circuit board?

Accepted Answer

Thermal resistance junction-to-solder point (Rth j-s)

Answer

Rth j-s (junction-to-solder-point thermal resistance) quantifies how efficiently heat moves from the LED die to the board, enabling comparison between packages.

(CLC) Certified Lighting Consultant Practice Test

(CLC) Certified Lighting Consultant Practice Test

CLC Light Source Technology & LEDs 3