# Low, Med, High Lighting - what does it all mean?



## Nubster (Aug 9, 2011)

Low light plants mean just that...they only require low light to thrive. However many low light plants will do really well under medium and high light...like Java Fern for the example. There's some that are low light plants that really only do well under lower light...so they should be placed in a shaded area of the tank if you are using medium or high light or just left out altogether. There is a chance that a plant may melt or otherwise take a dive if going from low to high light but then will come back. So...for many/most plants...it's fine to mix lighting requirements as long as it's under the higher light. A lot of plants that are high light will do poorly under low light or grow in a much different way than they would under high light which is likely undesirable. So it works well one way, but not the other.


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## Seattle_Aquarist (Jun 15, 2008)

Hi Aqua07,

Low, medium, and high light used to be based upon the number of watts per gallon when T12 and T8 fluorescent tubes were used as the light source. When T5 lamps came into being along with MIRO 4 reflectors the 'watts per gallon' didn't really apply but was still used by some. The saltwater community adopted the use of Photosynthetically Active Radiation (PAR) to define the amount of light. Actually what is being measured is the Photosynthetic Photon Flux Density (PPFD) first where the number of light photons per second measured over a square meter provides a quantitative measurement of light. Cara Wade from Build My LED did a great talk on the subject of lighting in October of 2015 at my local club, GSAS.

That may be more than you wanted to know but in the planted tank community we have (somewhat arbitrarily) decided that the following PAR levels / light levels correspond as follows:


> PAR Values
> Values between 10-30 are considered low light.
> Values between 30-80 are considered medium light.
> Values between 80-120 are considered high light.
> Keep in mind that these values are what is currently accepted by the community as accurate, and aren't set in stone.


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## Quagulator (May 4, 2015)

I would like to chime in, and emphasis the importance of what @Seattle_Aquarist mentioned --- "Keep in mind that these values are what is currently accepted by the community as accurate, and aren't set in stone."

This statement could not be more true. There is no specific line you cross going from low to medium to high light plants. I have a tank currently running with extremely high light, yet the majority of my plants in that tank do very well under less than a 1/4 the amount of light I am providing them. Many "high light" plants can grow at lower light levels if, lets say, you provide ample CO2 and nutrients. Sometimes they grow in a different manner such as growing up instead of across the substrate, growing large/branching leaves instead of small compact leaves, or having more stem length in between leaflets when grown in lower light than their ideal level, all of which are adaptations of the plant stretching for as much light as possible to suit its needs.

Also generally speaking, the less light you have, the slower plant growth there is. Take a low light crypt in a low light tank compared to the same cultivar of crypt in a high light tank, both of which have equal amounts of nutrients/CO2 and the crypt in the high light tank will grow faster. This is generally speaking, but it offers reason as to why a high light tank requires higher CO2 concentrations and nutrient levels to combat algae.


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