The Power in your Light
Light for plants is measured in micro-moles shining on a square meter. For example, full-sun at noon on the equator is 1990 μmols-m2-s1. (1990 micro-moles per square meter per second). To measure the light-energy for a photoperiod, multiply the micro- moles by the total seconds in the photoperiod and divide by 1 million….
1990×3600×12÷1,000,000 = 86 moles (DLI)
…which is also referred to as the Daily Light Integral (DLI). To add some perspective, the highest DLI recordings in the USA are in the Californian desert at 45 DLI. These measurements relate to the Photo synthetically Active Radiance (PAR) of the solar light-wave, which is between 400nm and 700nm.
A new HID 1000 watt ballast and lamp should be capable of generating 1990 μmols-m2-s1 one foot from the lamp or light point. As light travels its intensity deteriorates. For example, at 19 inches from the light point, the micro-moles are calculated thus:
1990÷(19″÷12″)2 which resolves to 794 μmols-m2-s1 or a DLI of 34. About the light saturation point for green-leaf photosynthesis.
Inverse Square Law tells us the power produced by a grow light decreases the greater the distance from the bulb. Spacing plants in growing enclosures presents a gardener with the paradox of how to achieve an optimum Leaf Area Index (LAI) while fully covering the plant canopy with direct-light at the right intensity.
You could be losing up-to 60% of your light energy because static lighting lacks an ability to diversify itself to maximize your plants absorbing surfaces at the right intensity. Moving your light offers the grower considerable flexibility in terms of plant to lamp tolerance, spacing plants, and provides light intermittently on the same leaves 40% of the photoperiod at the correct intensity so the maximum LAI (Leaf Area Index) can be achieved.
Leaf Area Index – is a measure of the total upper leaf surface area exposed to direct- light in relation to the area of ground that a plant occupies.