Led Grow Light Guide 2 — Questions and Answers
Question 1: What unit measures the amount of photosynthetically active light reaching a plant's canopy per second per square meter?
- PPFD (μmol/m²/s) (Correct answer)
- Lumens
- Lux
- Kelvin
Correct answer: PPFD (μmol/m²/s)
PPFD measures photosynthetic photon flux density at the canopy in micromoles per square meter per second.
Question 2: Which light spectrum range primarily drives vegetative leaf growth in plants?
- Blue (400-500 nm) (Correct answer)
- Green (500-600 nm)
- Far-red (700-780 nm)
- Ultraviolet C
Correct answer: Blue (400-500 nm)
Blue light promotes compact vegetative growth and strong stems.
Question 3: What does the term 'DLI' stand for in indoor growing?
- Daily Light Integral (Correct answer)
- Direct Lumen Index
- Dynamic Light Intensity
- Diode Light Input
Correct answer: Daily Light Integral
DLI is the total amount of PAR light delivered to a plant over a 24-hour day.
Question 4: Which spectrum is most associated with promoting flowering and fruiting?
- Red (600-700 nm) (Correct answer)
- Blue (450 nm)
- Cyan
- Pure white only
Correct answer: Red (600-700 nm)
Red light strongly stimulates flowering and fruit development.
Question 5: What is a key advantage of LED grow lights over HPS lights?
- Lower heat output and higher energy efficiency (Correct answer)
- Higher electricity use
- They emit no usable spectrum
- They cannot be dimmed
Correct answer: Lower heat output and higher energy efficiency
LEDs run cooler and convert more electricity into usable light than HPS fixtures.
Question 6: Hanging an LED grow light too close to seedlings most commonly causes what problem?
- Light burn and bleaching of leaves (Correct answer)
- Excessive stretching
- Root rot
- Nutrient lockout
Correct answer: Light burn and bleaching of leaves
Too-intense light at close range bleaches and burns the upper leaves.
Question 7: What does 'PPE' (photon efficacy) of an LED fixture describe?
- μmol of light produced per watt of power (Correct answer)
- Total watts consumed
- Color temperature in Kelvin
- Lifespan in hours
Correct answer: μmol of light produced per watt of power
Photon efficacy measures how many micromoles of light a fixture produces per watt.
Led Grow Light Guide 2
What unit measures the amount of photosynthetically active light reaching a plant's canopy per second per square meter?