Chapter 2 "Myths" Flashcards
Myth 1: Lumens = Photosynthesis
Measuring light intended for photosynthesis in __________is just plain stupid.
Lumens
A ____________________is a measurement of how much light the human eye perceives.
______________________measure the total amount of human visible light that comes from a particular light source.
a lumen (scientific symbol: lm)
Lumen
Humans use most of the “visible light range” between ________nm and ______________nm but our eyes are focused on 500–600nm, mostly the______________ and ________________portions of the spectrum.
400nm and 700nm
Green and Yellow
Plants have a completely different response to light, focusing their absorption around ________nm an __________nm (blue) and _______nm and 700nm (red).
400nm and 500nm
600nm and 700nm
Plants have a completely different response to light, focusing their absorption around two color spectrums:
400nm–500nm ______________.
600nm–700nm ______________.
Blue
Red
Plants focus their light absorption around the following spectrums:
—
Blue, 400-500nm
Red, 600-700nm
Plants also absorb some light in the rest of the visible spectrum as well as non-visible light in the _____________ and ____________bands.
Ultraviolet
Infrared
When it comes to garden lighting, it’s time to stop thinking in lumens and start thinking about __________________ (PPFD).
PPFD describes the density of _______________reaching a particular ________________.
Photosynthetic photon flux density
Photons
Surface area
PPFD is measured in _______________________which is a more useful measurement for the light your plants receive than lumens.
Micromoles (umol), per meter sq, per second
You need a __________________meter to measure how much photosynthetically active light energy is actually reaching your plants.
When testing LED grow lights, make sure to pick a quantum flux meter that is specifically designed for LEDs
Quantum flux
Light “color” is measured according to the _____________scale with blue having _____________values and ____________lower ones.
Kelvin (K)
Higher
Lower
Daylight color definitely shifts across the duration of a single day.
Sunlight starts out in the morning at approximately _________K (orange), climbs above ___________K (white) at midday, then drops back to ___________Kor lower at sunset.
2000K
5000K
2000K
daylight color of ………
2000K _________________
5000K __________________
Orange
White
Daylight-sky color temp can climb as high as _______________on a sunny summer afternoon. This falls in the ______________color spectrum.
8,000K - 10,000K
Blue
Many gardeners use only one type of HID light for their entire grow, and that includes the 3 types of HIDS; ___________, ___________, _______________lamps. None of these gardeners has any trouble “flipping” their gardens from vegetative to fruiting/ flowering.
MH
HPS
CMH
Many gardeners use only one type of HID light for their entire grow, and that includes MH, HPS, and CMH lamps. None of these gardeners has any trouble “flipping” their gardens from vegetative to fruiting/ flowering. WHY????????
They simply changed the photoperiod—the length of time the lights are turned on.
Plants that are sensitive to day length flower when their________________, not when the ______________of the light they receive changes
PHOTOPERIOD
COLOR
Most LED grow light manufacturers provide realistic power ratings and coverage area recommendations for their lights.
It would be ideal for LED grow light manufacturers to publish the power of their lights in _____________________at set height intervals
Micromoles
LED emitters have a _________________hour-plus life-span, which is about 10 years if used 12 hours a day,
50,000 hour
Myth 6: LEDs Won’t Burn Plants
One of the biggest myths about LED grow lights is that they won’t burn plants no matter how close they’re positioned to the plants. This myth is based on the light’s relatively low heat output and the idea “the more ____________the better.”
With today’s high-powered units, it’s easy to exceed the __________________ for plants.
Photons
Light-gathering limits
When hung too close to plants, LED grow lights can cause ____________________, also known “light bleaching.”
This occurs when more light is absorbed than can be processed by the plant.
Photooxidation
With Photooxidation……..those portions of the plant that are closest to the light—often the biggest flowers, unfortunately—turn white because their ___________________ destroyed.
chlorophyll
Light-loving plants need a more _________________spectrum to grow properly.
Complete
What is an LED?
LEDs differ from HID lamps in that they use a ______________________to produce light instead of creating light from hot, glowing gas plasma.
LED is an acronym for light emitting diode.
Semiconductor Diode
When an _________________is passed through an LED, a tiny chunk of material at the center of the emitter called a “___________” glows a particular color depending on the material it’s made from.
Electric current
Die
The die sits in a reflective cup to direct the light outward through an affixed ____________lens, and then the entire thing is enclosed in an _______________ case.
Epoxy
Epoxy
