Lighting for indoor plants

plant lighting study
Plants need light to grow.
When we install plants in areas with low access to natural light, we tend to compensate for this deficiency with artificial lighting. The problem comes when we overcompensate. The obvious issue here is artificial lighting = electricity = cost. Now, if we know how much lighting the plants really need, we provide just enough to keep them alive while minimising cost.  
In some way, plants ‘eat’ light. It’s like how we eat. Breakfast, lunch and dinner. Tea breaks in-between. Some people like to have a heavy breakfast and eat less throughout the day, while others might want to spread it out more evenly throughout the day. Point is, you’ll be ok if your daily cumulative food intake does not fall below a certain threshold.

It’s the same for plants. You can shine a 150 W metal halide lamp at them for 10 min, and it will probably be the same as pointing a 15 W lamp for 100 min. You can expect the phyiology behind this to be much more complicated, but that’s the rough idea.


The total light absorbed by the plant is termed the “Daily Light Integral” (DLI).

We exposed 2 species of plants to different DLI levels. The plants are:

– Philodendron Gold

– Dracena Surculosa

The DLI levels range from 4 molm-2day-1 to 0 molm-2day-1. (In layman terms, from a bit of exposure to light to complete darkness).

This experiment has been going on for 16 weeks. We should be wrapping up in 2 – 3 weeks.

From this experiment, we can see how low the lighting level can go for these 2 plants before they croak.

The purpose of this experiment is to answer the qn: If I am providing artificial lighting for indoor plants, how do I keep my lighting bill as low as possible?

By finding the minimum lighting levels needed for each plant, we can turn the lights off after we know they have had their fill. This means savings electricity and $$.

– T

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