Why is light important? 1.) Photosynthesis (chl & light) 6CO H 2 O (chl & light) C 6 H 12 O 6 + 6O 2 + 6H 2 O 2.) Needed for chlorophyll production 3.) Photomorphogenesis - development of certain plant parts, esp. flower initiation and development, seed germ...

Why is light important? Anthocyanin 4.) Anthocyanin production 5.) Light is energy! Some is converted to heat when it strikes a plant surface 6.) Light influences translocation in the plant 7.) Light can affect abscission (dropping of plant parts) when intensity suddenly changes

Light intensity - Refers to brightness - Often the limiting factor for growing or maintaining plants indoors

Light measurement Light can be measured in many ways! - Light meter (photoelectric cell) Footcandle Footcandle = the unit of illumination equivalent to that produced by a standard candle at a distance of 1 foot Lux Lux = the unit of illumination equivalent to that produced by a standard candle at a distance of 1 meter

Conversion Conversion: 1 fc = 11.1 lux These units measure only visible light (what the eye can see!) light quantity For scientific reporting of light quantity, you might hear the following terms: candela lumen photon flux quanta joules

Natural 1.) Natural (sunlight) Artificial 2.) Artificial (bulbs and tubes) 3.) Combination of the above Sources of light for an interior

Sunlight Factors affecting light penetration into a room: Windows 1.) Windows -type (glass/plastic/glazing) -reflection -barriers (overhangs, screens, curtains, shades, buildings and plants outside, dirt, etc...) -orientation (N, S, E, W)

Sunlight 2.) Latitude ( distance away from the equator) J F M A M J J A S O N D J J F M A M J J A S O N D J (calendar year) Burlington Atlanta Equator

Sunlight 3.) Geographic region -annual cloud cover -atmospheric pollution -humidity -elevation

Artificial light Supplemental to sunlight -extend hours of light intensity -increase intensity of light Sole source -role: room lighting plant lighting combination

Considerations not necessary with sunlight: spectral emission = range of colors produced by the light Light Quality!!! Artificial light orange violet blue green yellow red indego Visible Light (nanometers) Gamma rays X-rays Ultra- violet InfraredRadio

PA RPAR) Photosynthetically Active Radiation (PAR) Range = nanometers Based on length of each wavelength of light ~~~~~~~~~~~~~~~~~~~~ Chlorophyll blue430 red 670 Chlorophyll and associated pigments utilize light energy primarily in the blue (430 nm) and red (670 nm)

Choosing artificial lights Sources: Incandescent bulb Pros Pros: - -small - -no special fixtures - -dramatic - -range of wattages available Cons Cons: - -light is concentrated - -7% of energy usable light - -90% of energy heat! - -short life (750 hrs.) -red/orange blue -high in red/orange & low blue

Fluorescent tubes (cool-white, warm-white, daylight) Pros Pros: - -diffuse light, new fixtures avail. - -efficient! (7x incandescent!) - -22% of energy usable light - -cool! 36% of energy heat - -last 8, ,000 hrs (15x longer than incandescent!) Cons Cons: - -work best if o F - traditional - traditional fixtures bulky - -low far-red emission - -contain mercury -emit ultraviolet light

Coolwhite Warmwhite

Daylight fluorescent vs. Incandescent bulb Fluorescent Incandescent Relative energy (nanometers)

Pros Cons Sodium vapor lamps (HID lighting) Pros: % of energy visible light Cons: -yellow/orange/red spectral emission only! -large ballast (requires special lighting fixtures)

What happens when light contacts a leaf? Reflected Transmitted Absorbed

Ways to increase artificial light: Added white reflectors to fluorescent fixtures Paint surrounding walls white Regularly clean tubes to remove dust Regularly clean plants to remove dust Change tubes regularly Keep plants centered under fluorescent tubes

Natural vs. Artificial light intensities 10,000Noon sun during summer can measure 10,000 fc Cloudy winter day: 500-2,000 fc 1,300Inside rarely exceeds 1,300 fc –typical office fc –typical living room day: 10-1,000 fc night: 5-10 fc

Minimum light required for plant maintainance??? 100 fc

-Light quantity- Total light per day = footcandles of light x hours of light/day Example: 100 fc x 16 hrs of light/day 1,600 fc hours/day Sometimes, extending the daylength can compensate for a lower light intensity...