Monday, April 25, 2011

Light Meters / Photometers

One of the most important sources of energy for plants is sunlight, but did you know that not all plants like the same amount of light? Tropical plants can be some of the pickiest when it comes to light requirements. In a rainforest most of the light coming from the sun is absorbed by tall trees, yet a small amount of light can get through which is absorbed by smaller plants near the ground. These plants below the canopies enjoy their shady environment, and in fact, thrive in it. Basically not all plants require the same amount of light. How do you know how much light a plant needs then? Often times nurseries will sell plants with labels that have their light requirements, if they don't, the internet is always a good source for this information.

Most of the time you can just tell how much light a plant needs based on what kind of plant it is. Generally trees and tall plants require full sun while low to the ground plants generally like full or partial shade. Many plants can survive in shade or sun, but others are extremely sensitive and can be killed by too little or too much light. Fast growing annuals such as beans are a great example of a plant that will die without adequate light levels. This is because bean sprouts grow too tall and end up snapping their stem or falling over (in an attempt to get more light). On the other end of the spectrum, orchids can easily be harmed by too much light. In fact, light meters are very useful tools for orchid growers because different species of orchids require different levels of light.

What does a photometer do?
A photometer is another name for a light intensity meter, an instrument that measures the amount of light that it is receiving. This is very important because the human eye has a very hard time at distinguishing light levels. For instance, the difference in light levels in a well lit room compared to outside are huge. Inside my house, my light meter can hardly even register a few foot candles (a unit measuring light intensity), yet in the sunlight there is between 5,000-10,000 foot candles! So if you don't have a green brain, one of these light meters will help you decide where to put plants to optimize their potential.

Below you can see the left picture was a reading taken from inside my house, while the picture on the right has the meter facing the sun.