How are Lumens Measured and PAR Overview for Indoor Gardens

measuringbulb

measure light output

Here is an important concept and a tool that you need to learn about and use to properly measure the light output of your grow light setup, to help you achieve maximum plant growth while minimizing electricity costs.  I’m talking about measuring LED lumens using a light meter. This tool tells you how much actual light is being produced, versus electrical power consumption.

Are you already using a light meter to help grow your business?  If not, read on. I give you some useful explanations, and also below I review and recommend top 5 light meters, one of which I suggest you invest in for your growing business.

Another very important concept to know about is PAR, which deals with plant light spectrum. Read on to learn more below.

What is a Lumen?

When dealing with LED lighting one needs to think in terms of lumens not watts, whether replacing the old incandescent bulbs in your house with new LED bulbs or whether you are installing LED grow lights for a large-scale industrial grow farm.  As we all know, traditional incandescent bulbs measure their light output based on Watts, a 100 Watt bulb for example. But as we’re also painfully aware, those things get HOT since much of that energy in old-style bulbs is actually getting dissipated as heat rather than light. And while wattage does help explain how much energy is being consumed, it’s not a good way of measuring light output.  I’ll explain why.

This fancy term lumen is basically just a standard unit of measure of the “amount” of light produced by a given light source, in other words the luminous intensity of the light source. Historically, this goes back to the original way of measuring light using the standard output of 1 candle power.

In addition, there’s another important term you might hear about, called “lux” which is related to lumen but lux gives you a better measure of how focused or spread out the light source is. Think of the difference between a regular bulb and a laser; a laser focuses all the light in one point and therefore has a very high lux value, compared to a regular bulb that produces more diffuse spread light. So this is about as detailed as I think we need to get right now, but of course you can always get more info at Wikipedia here.

Long story short, more lumens = more light.

Remember, more watt does not necessarily give you more light (just a higher electric bill, ouch!) A more appropriate way to think is in terms of lumens per watt, which is also called “luminous performance” or “luminous efficacy” and essentially tells you how efficient your light source is in terms of lumens per watt.

So now you can understand how two sources, say a regular bulb and an LED light, could both potentially produce the same amount of light but they will each consume a very different amount of energy (watts). I think it is common knowledge that LED lights are WAY more energy efficient at producing light (lumens) for a given amount of energy.

What is PAR? Overview

As I’m sure you know, the reason plants are green is because they actually reflect most green light, while they absorb most of the rest of the light spectrum. This means that plants don’t really need green light, because for some reason green light doesn’t have the proper energy content to promote photosynthesis in plants. Yet the light at the other ends of the spectrum, namely orange, red, Infrared, as well as blue, violet, and even Ultra-violet, are just the kind of light that plants need.

Understanding Plant Light Spectrum

photosynthesis PAR
As shown in the spectrum diagram above, the white curves represent the typical plant response to light, in terms of the photosynthesis chemical reaction that occurs inside the plant as it absorbs light energy to create food for itself. You can see a big dip in the white curve around the green & blue-green regions, this is the light that is relatively useless for them.

However, in the same diagram above you see the white curves peak in the violet regions and deep orange and red. This is the kind of light that plants love and need to grow and bloom. The best grow lights are the ones that are tuned and designed to deliver these particular plant light spectrum bands that the plants need. There is absolutely no reason for your artificial lights to be producing green light, that is just a total waste of energy.

The beauty of LED lights is that manufacturers are able to finely tune the spectrum to deliver the appropriate light, therefore minimizing wasted energy. No other light in the market, except LEDs, gives you this benefit.

So, based on the above discussion you can see that LED grow lights give you two main benefits:
– More Lumens of light output per Watt
– More usable plant light spectrum

What is PAR Measurement?

In addition to understanding what is a Lumen, you should also understand what is PAR. PAR is an abbreviation for the scientific term Photosynthetically Active Radiation. This is just a fancy term for describing the type of light spectrum that plants use. Generally, this covers the wave band (spectral range) of solar radiation from 400 to 700 nanometers which is also in the range of visible light.

But unlike the human eye, plants prefer light at both ends of that spectrum. This is the light that photosynthetic organisms are able to use in the process of photosynthesis. So ultimately, you want to look for a plant grow light that mimics this range of light.

Most LED grow lights provide you with a PAR measurement, which is a measure of the photosynthetic photon flux (area) density, or PPFD. You may see reference to PPFD in the light specs.

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Top 5 LED Light Meters

First, here are my picks for the top 5 LED light meters. If you’re serious about maximizing growth, you really should add one of these to your toolbox. Careful not to just buy a cheap one that won’t work with LED lights. These listed here should do the job for you.

Amprobe LM-200 LED Light Meter

This model is basically a dual-scale meter that has the capability to measure 40,000 foot-candles or 400,000 Lumens per square meter of LED light sources. For altitudes below 2000 m, this light meter is fitted with a filter and a silicon diode sensor. With a built-in memory embedded, you can store up to 99 records at a time and there is a data hold that usually freezes the readings which appear on the display screen. Maximum recording will display the highest reading and there is an angled light cosine correction which is used for angle light projection. It is powered by a 9V battery and comes with a 1.5 m wire used for positioning of light sensor.

Amprobe LM-120 Light Meter

The Dual-Scale meter supports multiple light sources such as high-pressure sodium, fluorescent, metal halide and many other incandescent sources operating up to 20,000 foot-candles or 200,000 lumens per square meter. Furthermore, you will also get zeroing functionality and auto-ranging feature. For altitudes below 2000 m, these are fitted with silicon diode sensors. There is a protective sensor cap fitted with a 1.5m wire and a 9V battery. The zeroing capability of this model resets to the null point and the cosine angle correction adjusts in case of angled light.

Fluke 941 Light Meter

This model is compatible with four different sources of light namely high-pressure sodium, incandescent light sources, metal halide lamps and fluorescent lamps. The testers are immensely reliable and provide the precise measurement of the amount of light falling on a particular surface area. Also, with data retention and automatic shutdown feature, you will be able to save more battery and use it for longer periods of time. Weighing approximately 220 grams, this is one of the highly recommended light meters for people who are engaging in growing indoor-crops such as cannabis.

Extech LT40 LED Light Meter

This is a relatively economical light meter that is available in the market with multiple functionalities. It measures all the conventional sources of light as well as LED lights with better performance especially in case of color LEDs and white light LEDs. It measures the amount of light falling on a surface in Lumens per square meter or foot-candles depending upon the preference of the users. Also, it comes embedded with an LT40 protective sensor, a storage pouch, two AAA batteries and a user manual.

Extech LT45 LED Light Meter

This model specifically measures the amount of LED light falling on a surface and also measures conventional light sources, but is more preferable for the former. You can measure the amount of light in Lumens per square meter or in foot-candles upon your preference and the reading will be precise owing to the sensors that this model comes fitted with. This model additionally comes with a 9V battery, a hard case, a protective sensor cover and a user manual.
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Background…

LED – Light Emitting Diode

You may be wondering why LED lights are so dang better at producing light. The Light Emitting Diode, LED, is fundamentally a semiconductor device and works following similar principals as transistors and other micro-electronics of the modern age. In some sense, and single LED is a lot like a transistor, but it’s designed to emit light. The semiconductor industry has made significant progress in the last several decades, as more and more transistors are being shrunken down and packed onto a micro-chip, which is why our smartphones and computers keep getting more and more powerful, yet they are not getting bigger and bigger. Similarly, LED’s are being packed closer and closer together, and being designed to produce maximum amount of light while the actual electronic components are getting smaller and use less energy. LED’s are now EVERYWHERE it seems, even in your TV, your computer, your smartphone, your smartwatch, and now they’re even in your grow room!

Another thing to keep in mind is that LED lights, or diodes, can produce light in different colors depending on the application. Each color is a different frequency, but they can also be combined to produce new colors. And in recent years, the industry made a major achievement in figuring out how to produce pure white light using LED technology.

Noble Prize in Physics for Blue LED

LEDblue_free

Blue, green, and red makes white.

One of my favorite news stories about this has to with the invention of white LED, or more specifically blue LED. You see, the 2014 Nobel Prize in Physics was awarded to a team of Japanese scientists from Nagoya University in Japan, credited for inventing the pure Blue LED.

What’s the big deal you ask about a blue LED? Well before the blue LED was invented, the world had red LEDs and green LEDs and even some other color LEDs, but we did not have pure white. Our inability to produce pure white light using LEDs was actually holding back progress and widespread adoption of LED bulbs in society. If LED lights were ever going to replace incandescents, of course we need white light LEDs. So when the blue LED was finally invented by Dr Akasaki and his team, now they could combine red-green-blue LEDs to produce pure white light and then voila!

Now thanks to these amazing scientists, LEDs are gaining widespread adoption and acceptance throughout society, and the world will be a better, greener place!

How are Lumens Measured

So as we’ve been discussing, what we want to focus on here is measure actual light intensity, not just energy consumed. So it helps to understand how to properly compare apples to apples or apples to oranges, as the case may be. Next is a brief guide offering you some rules-of-thumb (or should I say rules-of-green-thumb, get it!) for how to compare light sources accordingly.

Watts to lumens

When going from Watts to lumens, you need one key piece of information described previously, which is the luminous efficacy of the light source. Again, this tells you how efficient your light is, in terms of producing certain lumens per watt. LED lights have a higher luminous efficacy value as compare to incandescent bulbs. So then once you know that value, and you know how much power you are giving it in watts, voila you can determine the total lumens output, according to this equation:
lumens = power x luminous efficacy.

Let’s give you an example again of a regular incandescent bulb.
25W incandescent bulb, with 15 lumens/watt luminous efficacy gives 375 lumens of light (that is 25×15=375)
60W incandescent bulb -> gives off 900 lumens (lm)
100W incandescent bulb -> gives off 1500 lumens (lm)

Now, let’s compare that same incandescent bulb against an LED light source with luminous efficacy of 60 lumens/watt, therefore
25W LED -> 1500 lumens

Right there, you can see that a 25Watt LED can theoretically produce the same lumens as a 100W incandescent bulb. WOW! what a huge potential savings in energy costs! No wonder the whole world is moving towards LEDs.

Lumens to watts

Now if you want to calculate the inverse, that is going from lumens to watts, it’s just a matter of solving the same equation I described above, but filling in the known values and solving for the unknowns (remember algebra?) This equation is just:
Power(in watts) = lumens / luminous efficacy.

Let’s again look at the incandescent example, and say we know the bulb produces 1500 lumens and has a luminous efficacy of 15, so Power = 1500 / 15, which equals 100 watts.

How to measure lumens

OK so now that you understand the basic principles and math, the next question is how to measure light, or how to measure lumens? Well, of course if you are buying a bulb, the manufacturer will just tell you how many lumens it produces. But there’s also a convenient, hand-held device that one can use. It goes by many names, such as light meter, photo meter, lux meter, lumen meter, etc. I just like to call it a light meter for simplicity.

What is a light meter?

As mentioned above, a light meter is a device which measures the quantity of light that is present in a particular area. Often, light meters are used extensively by photographers who refer to them as exposure meter. Photographers use them in order to determine the time of exposure required for their photographs. Some cameras have built-in light meters, and such devices will automatically make adjustments to aperture settings of your camera along with film speed and shutter speed. With the help of these three factors, it will compute exposure settings that will be preferable for your camera.

Many light meters, including the ones I review below, are hand held and intended for various purposes. It contains a special kind of light sensor, or photo sensor, that is sensitive to the light intensity. There are generally two types of light meters that are being sold in the markets, either incident-light meters or the reflected-exposure ones.

Incident-light meters are devices that are used to measure the amount of light that is falling on a surface. These light meters come embedded with a spherical light sensor that is placed on the area. In this way, the amount of light reflected from the subject does not hinder the calculation process of the amount of light falling on the surface and it gives precise reading. Thus, reflected-light meters are mostly meant for average scenes to calculate the exposure rate.

Reflected-light meters are better for capturing the amount of light falling over landscapes instead of incident light meters. Many a times, people tend to use reflected-exposure meters in order to compute readings of incident-light. All you have to do is keep the reflected-light meter near to the subject.

But there is one question that still remains unanswered. Whether these light meters are effective only for conventional sources of light, or can we use them to measure LED light sources as well. Since every form of light has its own frequency and wavelength, these light meters are considered to be versatile and can give you precise readings devoid of the source and type of light that is falling on the subject. But some light meters are specifically designed to measure LED lights, while others are multi-purpose, while some do not handle LED lights measurements (buyer beware, stay away from light meters that do not work with LED lights, read my product reviews below).

Use Light Meters for Growing

If you are reading this article, you are probably a professional grower looking to maximize your plant growth while minimizing cost. Everyone who has tried to setup a grow operation knows that one of the BIGGEST cost factors is electricity. Those old-school bulbs burn very hot and waste a LOT of energy, wasting you money. Not to mention, the traditional grow lights cause excessive heat, which then requires installing cooling fans in your grow room, which adds to the overall cost of your business! Stop the insanity! Time to get smart…

So why do you need to use a light meter in your grow operation? Well, so you can measure the light of course, duh! Seriously, just because you setup an LED light fixture, doesn’t mean that it will produce the same even light throughout your whole grow room. Undoubtedly there will be some dark zones and shadows caused by growing plants. So you cannot assume that the 2000 lumen lamp you used when your plants were young, will still work when your plants are mature.

The BEST thing to do is get yourself a handy dandy light meter, and periodically take light readings at different spots within your grow area. This will allow you to adjust the lighting accordingly in order to maximize your plant growth. Maybe you discover you need to put another light in that far corner of your room, or maybe there’s too much light in one area, etc. Of course, your plants will tell you if they’re not getting enough light, but you don’t want to leave things to chance! Man, this is a business, it’s about making money, so you have to approach your grow operation like a business, and optimize it and maximize your returns.

A light meter is a great investment, and in my opinion it is one of the essential tools of a SERIOUS grower who is in business to make profit. As such, I have reviewed what I consider to be best top 5 light meters for your growing business! Remember, stay away from cheap general purpose LED light meters that may not give proper LED readings, and puts your whole crop at risk. But the best tools and equipment, and this will help you produce the best results.

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