Chapter 2 "Myths"

Question 1

Myth 1: Lumens = Photosynthesis

Measuring light intended for photosynthesis in __________is just plain stupid.

Answer 1

Lumens

Question 2

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.

Answer 2

a lumen (scientific symbol: lm)

Lumen

Question 3

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.

Answer 3

400nm and 700nm

Green and Yellow

Question 4

Plants have a completely different response to light, focusing their absorption around ________nm an __________nm (blue) and _______nm and 700nm (red).

Answer 4

400nm and 500nm

600nm and 700nm

Question 5

Plants have a completely different response to light, focusing their absorption around two color spectrums:

400nm–500nm ______________.

600nm–700nm ______________.

Answer 5

Blue

Red

Question 6

Plants focus their light absorption around the following spectrums:

—

Answer 6

Blue, 400-500nm

Red, 600-700nm

Question 7

Plants also absorb some light in the rest of the visible spectrum as well as non-visible light in the _____________ and ____________bands.

Answer 7

Ultraviolet

Infrared

Question 8

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 ________________.

Answer 8

Photosynthetic photon flux density

Photons

Surface area

Question 9

PPFD is measured in _______________________which is a more useful measurement for the light your plants receive than lumens.

Answer 9

Micromoles (umol), per meter sq, per second

Question 10

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

Answer 10

Quantum flux

Question 11

Light “color” is measured according to the _____________scale with blue having _____________values and ____________lower ones.

Answer 11

Kelvin (K)

Higher

Lower

Question 12

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.

Answer 12

2000K

5000K

2000K

Question 13

daylight color of ………

2000K _________________

5000K __________________

Answer 13

Orange

White

Question 14

Daylight-sky color temp can climb as high as _______________on a sunny summer afternoon. This falls in the ______________color spectrum.

Answer 14

8,000K - 10,000K

Blue

Question 15

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.

Answer 15

MH
HPS
CMH

Question 16

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????????

Answer 16

They simply changed the photoperiod—the length of time the lights are turned on.

Question 17

Plants that are sensitive to day length flower when their________________, not when the ______________of the light they receive changes

Answer 17

PHOTOPERIOD

COLOR

Question 18

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

Answer 18

Micromoles

Question 19

LED emitters have a _________________hour-plus life-span, which is about 10 years if used 12 hours a day,

Answer 19

50,000 hour

Question 20

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.

Answer 20

Photons

Light-gathering limits

Question 21

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.

Answer 21

Photooxidation

Question 22

With Photooxidation……..those portions of the plant that are closest to the light—often the biggest flowers, unfortunately—turn white because their ___________________ destroyed.

Answer 22

chlorophyll

Question 23

Light-loving plants need a more _________________spectrum to grow properly.

Answer 23

Complete

Question 24

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.

Answer 24

LED is an acronym for light emitting diode.

Semiconductor Diode

Question 25

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.

Answer 25

Electric current

Die

Question 26

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.

Answer 26

Epoxy

Epoxy