{"id":681,"date":"2017-02-28T10:37:43","date_gmt":"2017-02-28T15:37:43","guid":{"rendered":"https:\/\/designinglight.com\/?p=681"},"modified":"2017-02-28T10:37:43","modified_gmt":"2017-02-28T15:37:43","slug":"lighting-for-plant-health","status":"publish","type":"post","link":"https:\/\/designinglight.com\/?p=681","title":{"rendered":"Lighting For Plant Health"},"content":{"rendered":"

I have a current project with a green wall, aka living wall, and other greenery in the space. I\u2019ve been given conflicting information about the lighting requirements I need to meet are and how to measure them, so I did some research. This isn\u2019t definitive, but here\u2019s what I\u2019ve found.<\/p>\n

First of all, the measurement units that we\u2019re all familiar with don\u2019t apply to horticulture because the average plant\u2019s response to light is very different from that of the human visual system. We know that the human eye response curve is V(\u03bb) (pronounced vee lambda) which is shown in Figure 1. Our response to electromagnetic energy falls between 380 and 770 nm, with a peak response at 555 nm. In order to measure light the way the human visual system perceived it, V(\u03bb) is folded into the definition of the lumen, the footcandle, etc.<\/p>\n

\"\"<\/a><\/p>\n

Figure 1<\/strong> V(\u03bb)<\/p>\n

Plants, however, have a response curve called the photosynthesis action spectrum, shown in Figure 2. The wavelengths of light that are absorbed and used by plants are below 520 nm and above 610 nm [i]<\/a>, which roughly equates to the blue and red range of the visible spectrum. Plants need a great deal of red light, a far amount of blue light, and little or no green light.<\/p>\n

\"photosynthetically<\/a><\/p>\n

Figure 2<\/strong> Average photosynthesis action spectrum of chlorophyll [ii]<\/a><\/p>\n

So, we can\u2019t talk about the amount of light delivered to plants in a useful way if we\u2019re using lumens and footcandles. The measurement of light for plant health is Photosynthetically Active Radiation (PAR) [iii]<\/a>. There are PAR calibrated light meters, and digital tools to convert lux\/footcandle readings to PAR. Other common measurements are also not relevant to horticulture.<\/p>\n