Lux to PAR Calculator

What is PAR, and Why Does It Matter?

PAR (Photosynthetically Active Radiation) is the range of light wavelengths between 400–700 nanometers that plants use to do their photosynthesis magic.

Why does PAR matter, you ask?

Well, photosynthesis is kind of a big deal if you want your plants to thrive instead of just surviving.

During this process, plants absorb those PAR photons and convert CO2 and H2O into sweet, sweet glucose to fuel their growth.

More PAR = more food production = bigger, better plants.

It’s simple math, really.

Now, we can actually measure how much of this precious PAR light your plants are getting with a nifty metric called PPFD (Photosynthetic Photon Flux Density).

In layman’s terms, it tells us the number of PAR photons hitting a given surface area every second.

Lux — What Is It Good For?

Lux is all about measuring light intensity for human eyeballs. Plain and simple. It’s a quantification of how many lumens of visible light are hitting a given surface area.

So while useful for, you know, actually seeing where you’re going, lux tells you jack squat about the light plants crave.

Still, it’s kind of the OG measurement when it comes to lighting. That’s why those dirt-cheap lux meters are so widespread.

Now here’s the hard truth—lux is a pretty crappy metric for measuring plant lighting.

It completely disregards the all-important blue and red wavelengths that really get plants’ photosynthetic engines revving.

Instead, lux weights things heavily towards green light that has plants like, “Yeah…thanks for nothing, bro.”

And don’t even get me started on invisible light waves like UV and far-red that Lux can’t begin to touch. Those are prime plant fuels that could be missing from the lux picture entirely.

Lux meters may be flawed, but they’re a damn cheaper than a PAR meter.

How the Lux to PAR Calculator Works

The core concept is dead basic: You slap in your lux reading, the calculator divides it by a conversion factor specific to your light source type, and boom—you’ve got an approximate PAR value measured in units of μmol/m²/s.

Why do we need to convert, you ask?

Well, lux meters are calibrated to measure visible light intensity as perceived by human eyes.

Meanwhile, PAR quantifies the photon firepower in the 400-700nm waveband – the range that really butters plants’ biscuits for photosynthesis.

So we’ve gotta bridge that gap.

Here’s the magic formula powering this calculator:

PAR (μmol/m2/s) = Lux/Conversion Factor

Simple, right?

Plug in your lux level, divide by the conversion factor, and you’re well on your way to PAR estimation.

Now here’s the key factor: that conversion factor varies like crazy depending on your light source.

Think sunlight, LEDs, fluorescent, MH, and HPS—they all put out different spectral power distributions.

For example, sunlight gets a factor of 54, while cool white fluorescent is at 74. Metal halides sit around 71, HPS lamps go for 82, and typical white + red LED grow lights range from 55 to 65.

SIDENOTE: This calculation is just an estimate at the end of the day. For truly accurate PAR measurements, you’ll want a real quantum PAR sensor—no shortcuts there.

But as long as you know the limitations and use this thing correctly, it’s a solid way to ballpark your PAR levels.

Step-by-Step Calculator Instructions

Here’s how to put this bad boy lux to PAR calculator to work:

1. First, grab your lux meter, shine it at your grow lights, and jot down that lux reading.

2. Now, hop into the calculator and plug that lux number into the designated input field.

3. Next up, you’ll see a dropdown menu asking what type of light source you’re working with. Select from the options: sunlight, fluorescent, metal halide, HPS, or LED.

4. Once you’ve nailed down those inputs, click on the “Calculate PAR” button. That’s it—the calculator’s internal magic will do the rest.

In a flash, the calculator will spit out your approximate PAR value in units of μmol/m²/s. This tells you how many photosynthesis-fueling photons are reaching that sampled area each second.

A few pro tips before you get trigger-happy with those lux measurements:

  • Take multiple readings from different spots under your lighting to gauge the PAR distribution.
  • Sample directly at the canopy level where your plants are drinking up all that light energy.
  • If you get inconsistent readings, double-check that your light source is selected correctly.

At the end of the day, the calculator spits out approximations. Factors like your light’s specific spectral output can skew the accuracy a bit.

Dhruvir Zala

Meet your guide
Dhruvir Zala

I’m the guy behind Farmingram, where I nerd out on all things indoor agriculture. Through rigorous research, my goal is to get more people excited about where agriculture is headed.