Measuring Light
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Spectrum – “To Measure Is To Know” Measuring Light How Does the Sun’s Radiation Affect My Plant Growth? How do your plants feel today? 4LIGHT HAS ECONOMIC VALUE As the driving force for photosynthesis, light is fundamentally important to crop production. Plant growth and development is significantly influenced by both the quantity and the quality of light. Light energy is relevant to other factors too. The ET calculation (evapotranspiration) for irrigation scheduling uses solar radiation as a key variable. Leaf wetness periods or high humidity, which affect disease pressure, can be mitigated with sunny days versus cloudy days. It is essential that growers understand this important variable in order to efficiently produce quality plants. Effects Small influence on morphogenetic and physiologic processes, bleaches colors, causes sunburn, causes some fungus sporolation Ultra Violet Ultra Violet Blue Low absorption, stimulation of cell elongation, influence on flowering and germination, blocking may slow stretch HEAT - energy absorption is converted into heat Slight absorption by chlorophyll, influence on photoperiodism, inhibition of cell elongation, sunburn, causes some fungus sporolation High absorption by chlorophyll and carotenoids, big influence on photosynthesis Low absorption by pigments Low absorption by chlorophyll, big influence on photosynthesis and photoperiodism, blocking may slow stretch MEASURING LIGHT ACCURATELY REQUIRES THE RIGHT METERS AND METHODS

How Does Light Affect My Plant Growth? Human Eye Perception Foot Candle or Lux meters measure light similar to how the human eye perceives brightness: strongest in the 500-600nm range. Though this is desirable for photography and interior design, plants react to light differently. “Measuring DLI inside the greenhouse can be very revealing, since growers usually rely on their eyes to determine the light levels and the human eye is a terrible light sensor because it is so effective at adjusting to different light environments.” James E. Faust Associate Professor of Horticulture Clemson...

Spectrum – “To Measure Is To Know” LIGHT METERS Solar radiation The sun radiates a broad range of light from 300-1100nm. In agriculture, this total radiation is needed primarily to calculate Evapotranspiration (ET). ET is the amount of moisture leaving the ground through evaporation (from the ground) and transpiration (from the leaves), and is dependent upon light, wind speed, temperature, and relative humidity. UV (200-400nm) Plants can suffer from sunburn; exposure to radiation in the mid-ultraviolet part of the electromagnetic spectrum (UV-B) triggers stress responses, inhibition of...

Spectrum – “To Measure Is To Know” Measuring Light Individual light sensors, available individually or as a bar of 3 or 6 sensors, allow you to measure site-specific areas. These hand-held sensors feature cosine correction, built-in levels, and mounting brackets for stationary measurements. Light Bars are frequently used when measuring across a greenhouse bench. 3415FX 3668I 3668I3 3668I6 3676I 3670I Field Scout External Light Sensor Meter Quantum Light Sensor Quantum Light 3 Sensor Bar Quantum Light 6 Sensor Bar UV Light Sensor Silicon Pyranometer Sensor Leaf Area Index Leaf Area Index or...