Of all the elements required for plants to survive, light is perhaps the most important.  Without light, plants die very quickly.  But how do you know which plants will survive in the different light levels that are found in a building?  Will the same species thrive as well in a well-lit atrium as in a seldom-used conference room?  Can you get the 'look' you are after if the light isn't right?

This section of module 3 will help you find out how plants use light and how you can select plants that will survive under different light levels.

How do you know how much light you have?

The only way to be sure about the amount of light that is available is to measure it.

Different types of measurement

Light can be measured in several different ways, including the energy of the light, the quantity of light or the brightness of the light. Light meters are available that measure light in all these forms, but for our purposes, you only need to consider brightness (illumination).  Click here to find out about other types of light measurement.

The brightness of light as experienced by the eye (illumination) is measured in lux (foot candles in the USA.  1 lux = 0.093 foot candles, which means that there are approximately 10 lux to 1 foot candle). This is the form of light measurement that most interior landscapers and architects use.

What do we use to measure light?

The only way to accurately measure light is to use a light meter. NEVER rely on your eyes and your judgement about the light levels in a room, because your eyes adapt very quickly. No matter how much experience you have in specifying plants, you can never trust your eyes alone when making a decision about light levels.

Light meters, like any other scientific instrument are totally objective. They can only tell you how much light there is at the centre of the sensor at the time of the measurement. They cannot make allowances for the time of day, the direction of the sun or the type of window blinds that might be in place. However, they are fairly simple to use, just as long as you follow some straightforward rules.  Click here to download information on measuring light.