I. THE SOLAR RADIATION

        1. Nature of Radiation

                -Electromagnetic spectrum (wave or particle)
                -Measured b wave length and frequency

        2. Solar Radiation Reaching the Earth

                -Atmospheric Window (most visible, PAR)
                -Filtration by:

                            Ozone Filter (ultraviolet light, long wave light)
                            CO₂ Filter (infrared light, heat waves)
                            Water Vapor Filter (Far red, infrared)

        3. Greenhouse Effect

                -The visible range light reaches the earth
                -The earth reradiates long rays (infrared) to atmosphere
                -Infrared light is absorbed by watervapor and CO₂ in the atmosphere heating the earth's atmosphere (as in a greenhouse)

II. MEASUREMENT OF LIGHT (LIGHT INTENSITY)

        1. Radiometric Measurement

                -Measurement of light energy
                -Units: Joules, calories, watts (watt m^-2)
                            1 Joule = 0.24 cal
                            1 watt = Joule ^. s^-1

        2. Photometric Measurement

                -Measurement of brightness
                -Units: foot candle, lux, µmol m^-2s^-1   (PPF, Photosynthetic photon flux)

             Conversions     1 foot candle = 10.76 lux
                                       1 lux = 0.1 ft. c.

                Example         A bright day                 Overcast day
 
                                       10,000 f.c.                    1,000 f.c.
                                        100, 000 lux                10,000 lux
                                        2,000 µmol m^-2s^-1        200 µmol m^-2s^-1

                For sun light conversion factor is 54
 
                                        lux /54 = µmol m^-2s^-1       (PAR)    or      µmol /m² sec

                                        Conversion factor (divisor)
                                        -incandescent lamp:             50
                                        -C.W. Fluorescent lamp:     74
                                        -H.P. Sodium lamp:              82
                                        -mercury                               84

III. THE LIGHT ENERGY BUDGET (PAR)

        Water traspiration                       (39%)
        Back Radiation from Soil            (34%)
        Reflection by Plants                     (20%)
        Heating Soil                                 (2%)
        Heating Air                                  (4%)
        Plant Growth (photosynthesis)     (1%)
                                                            (100% total recieved)

IV. LIGHTING FOR PHOTOSYNTHESIS

        1. Purpose

                -To keep the plant slightly abobe light compensation point (indoor plants)
                -To increase crop yield
                    for intensive agriculture
                    i.e. winter lighting of roses results in up to 20% yield increase for Valentines Day market

        2. Light Sources

                -Incandescent lamps not energy efficient
                -Use fluorescent lamps (daylight, cool white, etc)
                -Use HID lamps (high intensity discharge lamps)
                        high pressure sodium lamps
                        metal halide lamps
                        mercury vapor lamps

        3. Cautions

                -CO₂ must be enrched whan light intensity increased
                -keep temperature optimum
                -more labor to harvest
                -reverse day to night for growth rooms (tissue culture)

IV. LIGHTING FOR PHOTOPERIOD CONTROLS (LOW LIGHT INTESITY)

      1. Purpose
                -to keep short day plants vegetative (prevent flower initiation)
                -to flower long day plants under short day condition

      2. Light Source
                -use incandescent lamps (more economical)

      3. Recommendation
                -for day extension, light after sunset to 10 pm
                -Night break (11 pm to 2 am) more economical (short day plants)
                                     (1 am to 2 am)