GENERAL CULTURAL PRACTICES (Enviromental Conditions Required) – LIGHT

ENVIRONMENTAL CONDITIONS REQUIRED are included 1)Light 2)Temperature 3) Relative Humidity (RH) 4)Carbon Dioxide 5)Air Circulation and of course 6)Oxygen. I will cover one by one and we starts with light.
*Light: Two factors are important and can be affected by greenhouse structures and coverings (see also posts Greenhouse Control system-Light and Greenhouse Glazing material). NOTE: Both of these vary with plant species.

• Quality: Refers to wavelengths of light. (Remember in physics: light spectrum) Visible light = 390-760 nm: blue at the low end, red at the high end. PAR (photosynthetically active radiation) = between 400 and 700 nm (blue, yellow, orange and red… but not green)NOTE: This varies slightly for each plant species.
• Quantity: The quantity of light monitoring is very crucial especially in countries which have four season. The quantity of light is affected by both day length and sun angle (changes with season): 1)Day Length: eg. In North-West area in USA, day length on June 21 is 14 hours 15 min. On December 21 day length, however, is only about 10 hours. 2)Sun Angle: In June the angle is high = 81o from the horizon (almost overhead). In December the angle is low = 34o from the horizon. **The quantity (amount) of light reaching the Earth’s surface is therefore higher in Summer than it is in Winter. **For tomatoes in the desert southwest or other high light areas: During the Winter or times of low light the quantity of light available is enough to support 3 – 4 fruit/cluster.During Spring/Summer/Fall the quantity of light may be too high and shading may be needed. 4 – 5 fruit/cluster is typical. For Tropical countries like Malaysia & Thailand , the amount of light is almost consistent. But sometimes when droughts happens or at locations where sunlight are so intense, shading may also be needed to cut down some damaging effects from high intensity light of the Sun. This is crucial especially for Chillies and Melons grower.