Your whole life you’ve measured light in two ways watts and lumens. You’ve never deviated from that measurement because you’ve never had to, so why now? Well, it may surprise you to find that both measurements just aren’t very useful to plants. In fact, your plant just doesn’t care how many lumens your new grow light is. It cares about the PPFD or the photosynthetic photon flux density. But wait! The supplier for the light you’re looking at doesn’t list a PPFD rating, what now? Do you absolutely need to know this number? The answer? Yes.

What is a PPFD rating?

The photosynthetic photon flux density is a measure of the light’s photons that are capable of absorption into the plant. It’s important since lumens only measure light visible to humans, not how much is actually reaching the surface of your plant’s leaves – and being absorbed into the plant as nutrition.

So, how do you measure a lights PPFD? Well, it’s actually quite simple, which is why it’s surprising so many retailers don’t list the value. The machine to measure the output is a couple hundred dollars and gives out a reading almost instantly. The test as a whole is painless and gives a far more accurate reading of the light’s usefulness than measuring lumens.

Why don’t certain manufacturers provide the PPFD rating?

We can’t say for sure, however, a company could only have two reasons for not disclosing information. One, they aren’t experienced enough in the field to know what measurements are needed to sell grow lights to knowledgeable customers. Two, their product has an extremely low PPFD that will discourage the customer from purchasing the item. Either way, sellers who don’t disclose the PPFD are sellers you don’t want to buy from. Could you imagine buying a computer from someone who doesn’t know what an operating system was? Or buying a house from someone who isn’t sure of the square footage. In both cases, you would run from the seller – and it’s the same when buying grow lights.

What can I do when buying a grow light?

Choose a supplier that markets their product well, provides you, the consumer, with the information you need to make a knowledgeable choice and has a good return policy if the light doesn’t work as they advertised. There’s no replacement for experience and good business practices no matter what you’re looking for or buying.