Photosynthetic Photon Flux Density (PPFD)

Photosynthetic Photon Flux Density(PPFD) goes by various names, Quantum Light or simply Photon Flux. In all cases, it is a unit of measure to express the light quantity relating specifically to photosynthesis in units called micro-moles. The PPFD is expressed in micro-moles of photons per meter squared, per second (μmo/ms/sec). You could say, the PPDF is to PAR as Lux is to lumens. The prior is horticultural specific, while the latter, refers to the capacities of the human eye. A mole is a quantity, an amount, a very large amount. It is a number equal to the number of atoms in 0.012 kg of carbon-12. A micromole is one millionth of a mole.

Example Using PPFD Measurements

I have to hand it to Build My Led (BML), a company out of the USA. They do a great job of specifying their products. Below is a good example of good information, I found on their web site, offering a LED replacement equivalent to a 660watt HPS bulb. They give the exact wavelengths in nanometer (nm) units and the quantity of photons getting to the plant in PPFD, micromoles/m2/second (μmoles/m2/s). In order to do this you will have to know the distance of the light source to the plant. The distance they placed the fixtures, they ave posted as 10 inches.

HPS vs LED | Example

This LED complex is made up of five 48″ All-Purpose Red Growth Spectrum fixtures. It is designed to replace a 600W HPS system over a 4’x4′ growing area.  I admire their advertising because they give exact relevant information in an informed professional language. Your going to have to be familiar with that language in order to judge any fixture product intelligently. Unlike many companies using only descriptive adjectives (“the best”) rather than quality and quantities in the PAR range. This system delivers an average PPFD reading of 200 PPFD. The fixture mounting height was 10″ from the measurement plane, and provides increased uniformity over HPS. In addition, it is emitting only the PAR ranges a plant can use. All the while consuming 61% less watts.

Light Levels for Some Common Plants

 The table below provides a reference to light levels for a sampling of plants and sun conditions

  • House Plants 30 to 200 PPFD
  • Leafy Crop Plants (i.e. Lettuce & Basil) 200 to 600 PPFD
  • Tomatoes & Other Fruit Crops 400 to 1000 PPFD
  • Full Sunlight in Summer @ Noon 2000 PPFD
  • Full Sunlight in Winter @ Noon 1200 PPFD