Lumens vs PAR – What Is More Important When Choosing Grow Lights?

There are many things about grow lights that appear technical. Nonetheless, you should have sufficient knowledge of some of these technical details, if you will make a good choice of grow light for your plants.

When I was buying my first grow light, I felt unqualified to make an informed decision, as I knew next to nothing about the features to consider. One of the things I couldn’t understand at first was the meaning of and the differences between lumen and PAR. All I knew was that they had to do with light intensity.

If you are planning to start indoor gardening, then you need grow lights. In addition to the type of grow light, the light intensity is another thing you have to consider before buying one. In this article, I will compare lumens vs PAR, and help you decide which is more important to consider before choosing a grow light. I will also discuss some of the things you should consider in a grow light before buying one.

What Is Lumen?

The lumen is a unit of luminous flux equal to the light emitted in a unit solid angle by a uniform point source of one candle intensity. In simpler terms, it is a measure of the brightness of light from a source, as perceived by the human eye.

Going by lumens, the typical range of wavelengths used to measure light intensity ranges from 400 – 700nm. This is the spectrum that is visible to the human eye. However, the wavelengths at the center of this spectrum appear brightest to the eyes, while those at the far ends appear dim.

The wavelengths at the far ends – blue and red – are the most important for plant growth. These wavelengths appear quite dim to the normal eye, while most of the brighter wavelengths are not as essential to plants.

In essence, the lumen rating tells you little or nothing about the suitability of a grow light for your plant, as it is more of a measurement of brightness, and brightness is not the most important factor when it comes to lighting for photosynthesis.

Lumen would be the right factor to go by if you were choosing a light for illuminating a room. When it comes to plants, brighter light is not necessarily better.

What Is PAR?

Photosynthetic active radiation (PAR) light is made up of the wavelengths - in the visible 400 – 700nm spectrum – that drives photosynthesis. It is the range of light that is plants need to produce glucose. A light source may produce more wavelengths than plants need, the PAR is made up of those that plants make use of.

Lumen, as a measure of brightness, can be roughly appraised by the human eye. However, PAR cannot be perceived similarly. Instead, PAR is measured by the use of special quantum sensors.

These sensors can use either the yield photon flux (YPF) or the photosynthetic photon flux (PPF) weighting methods to measure PAR. The simple PPF weighting gives equal significance to all the wavelengths that fall in between the 400 – 700nm spectrum.

The downside of the PPF weighting is that it does not reveal how chlorophyll reacts to different wavelengths. On the other hand, the YPF weighting measures based on the sensitivity of chlorophyll to each wavelength in the spectrum.

What makes the YPF more interesting is that a wider spectrum of 360 – 760nm is considered to include infrared and ultraviolet wavelengths that are not visible to the human eye.

Which Is More Important to Consider – Lumen or PAR?

Since the lumen and PAR are different light intensity measures, it becomes critical to know which you should consider before you choose a grow light.

Lumen value is of less value when it comes to grow lights. For normal lighting purposes, it would help to consider lumen, as it is directly related to the brightness of a light source. However, the significance given to yellow light in the lumen scale is of less importance in indoor gardening, because it is not an essential wavelength for photosynthesis.

On the other hand, PAR is what you should consider. The PPF weighted PAR considers all wavelengths within the 400 – 700nm spectrum equally, yet it is still a better measurement of grow light impact on plants than the lumen value.

Nevertheless, if you are concerned with the intensity of the various wavelengths within the photosynthetically active spectrum, the YPF PAR is the standard. Typically, LED grow lights are heavy in the most essential blue and red wavelengths. So, you may not have to bother about the specific wavelengths produced, unless you have special requirements for your plant.

While lumen value is always the highest in the mid-section of the spectrum, the PAR reading will be highest at either end of the spectrum, near the 400nm and the 700nm range.

Other Things to Consider in a Grow Light

You should not make a grow light choice based on PAR/lumen alone. Some of the other features I’ve found critical in grow lights include:


This has to do with the level of energy used to produce light and the quality of the light output. In incandescent bulbs, the energy used is directly related to the intensity of lighting output. However, in LED grow lights, that is not the case.

LED lights are energy-efficient, and the energy used is not usually related to the quality of the output. What you should focus on is the equivalent of the output in HID power and the low power consumption.


You need a grow light that will offer coverage over a large area, without compromising light quality. If you want healthy plant growth, they should all be adequately covered by the light, even if it means getting multiple grow lights.

The distance at which you hang the lights from the plants will also affect the coverage. Coverage is always reduced at a lower level and increased at a higher level.

Cooling system

Another interesting fact about LED grow lights is that most of them come with cooling systems. While they do not produce as much heat as some other types of light, the perpetual emission of light causes heat buildup.

Go for lights that come with cooling fans and heat sinks that help with heat dissipation. In the absence of a cooling system, the lifespan of the light will be considerably shortened.


I hope this article has helped you understand what the difference between lumen and PAR is and what you should consider when buying a growing light. If you are a beginner in indoor gardening, if you don’t understand what lumen and PAR means, or which is more important to consider in a grow light, PAR is what you should consider. Lumen value is nothing more than a representation of how bright the light from a source is. What you want to consider in a grow light are the wavelengths useful to your plants.

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