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How To Measure Lumens?

How To Measure Lumens?

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Light and light bulbs. Lumens and lux. 

Most of us are well-versed with the first two. Not so much the last two.

Both are crucial light measuring units, albeit a little confusing. You probably agree with that, but you’re also wondering, how are lumens measured for light bulbs? What about lux?

Unlike what you might imagine, it’s easy to measure light. With the help of a few tools, you can do it in seconds. 

Read on to learn how.

How To Measure Lumens For Light Bulbs?

The lumen rating of a bulb is determined during manufacture. So as you buy the bulb, you can tell its lumen level because it’s indicated on the product.

Energy 101: Lumens

So you don’t need to measure the lumens. But you can test the bulb for other light metrics.

Analyzing the light level in a room can help you know the best spots for different activities. 

For example, you can tell where to place your study desk or couch and which corner to convert to a reading nook.

It’s common for different surfaces within a room to receive varying amounts of light, even when they all receive light from the same bulb.

Yellow lights hanging on the celling

How does this happen?

  1. The bulb releases the same amount of light in all directions. This is the lumen. 
  2. Varying amounts of light land on each surface in the room. This is illuminance, also called lux or foot-candle.

Let’s see an example.

You’ve installed a bulb at the center of your home office, and you want to have two tables in the room. 

You place Table A right below the bulb and place Table B in one corner of the room.

Switch on the bulb and measure the amount of light in both locations. 

The readings will show a higher reading on Table A and a lower reading on Table B.

Conclusion: Table A will receive more light than Table B because it’s closer to the bulb.

Using Light Meters To Measure Light

Light meter

To measure how much light is falling on a surface, use an incidental light meter . These light meters are digital and typically handheld.

A light meter can help you know how much light a replacement bulb is emitting. It can also help you arrange a space based on how light spreads across the room.

How light meters work

The light meter has a photodiode sensor, which detects the amount of light hitting the device. The sensor converts the light energy to measurable electrical energy. It then displays the readings on an LCD screen.

The meter displays light intensity in lux or foot candles. Most devices display both metrics and will have a Lux/FC button. Press the button to switch between lux and foot-candle readings.

Here is how to use the light meter

  1. Press the Power button to switch on the gadget. 
  2. Place the meter in front of the light and check the reading.
  3. Repeat this while moving the meter around the room. In doing so, you measure the light intensity in different spots across the room. 

In general, light meters record light intensity readings continuously. So you can see how the amount of light varies as you move around the room.

Most meters have a Min/Max button. Press this button to see the lowest and highest lux or foot-candle count.

Using Light Meter Apps To Measure Light

BEST LIGHT METER APP - How To Get The BEST Film Exposure (2021)

Light meter apps are an alternative way of measuring light. If you don’t have a handheld light meter, you can use this option.

The app uses your smartphone’s integrated light sensor. The sensor adjusts the light settings as you use the phone.

For instance, it will adjust brightness when:

  • You’re reading
  • Taking a photo or video

To use the app:

  1. Download and install your chosen app from the App Store or Play Store.
  2. Open the app and check the readings. If you can get a reading, it means the app is working. 

Some apps have a simple layout and display the reading on the screen. Others show a meter or graph with the light level readings. 

  1. Hold your phone with the screen facing the light and check the light level the app records. 
  2. Move closer to the light and check the light level it records. Move away from the light and do the same. 
  3. Now, compare the readings to see which locations have brighter lighting.

You may have to test a few apps to see which one works best with your phone. 

Unfortunately, you can’t tell how well an app works beforehand. No government agency is policing the app stores for quality compliance. So some apps may not be as good as others.

Even though the light meter app may be accurate and reliable, it may also be limited in some ways.

For example, the app may have hardware or software limitations. Because of this, it may only display readings up to a certain number.

Light Measurement Explanations

When buying lights, you’re likely to encounter these three terms: lumens, lux, and foot-candles.

You’ll also see these terms when looking at lighting recommendations for different spaces.


Decoration light bulb

Lumen measures the amount of visible light originating from a light source. The lumen level indicates how bright or dim a light is. It’s shown in numbers.

A high lumen number means more light and, therefore, more brightness. 

Bulbs have the lumen level written on their surface and the packaging. When you know how much light you need in a given room, you can pick the bulb with enough lumens to emit that amount of light.


A light bulb

Lux measures illuminance. Illuminance indicates the total amount of light falling on a given area.

Lux indicates how many lumens are falling on a square meter of a surface. It tells us how much light hits a given object at a specific distance from the light source. 

The lux amount decreases as you move farther from the light source.

Let’s say you have a bulb with 1000 lumens, and you light it over a 1 square meter table. The bulb’s light intensity will be equal to 1000 lux.

If you use the same bulb to illuminate a larger area, you get fewer lux and less brightness. So if you light up a 20 square meter room, you get 50 lux.

In the same way, if you use a 2000-lumen bulb to illuminate a surface area of 1 square meter, you’ll get 2000 lux. And if you beam these lumens over 20 square meters of space, you get 100 lux. 


Bright Light bulb

Like lux, a foot-candle is a measure of illuminance. It tells us how much light is falling on a given surface. 

The only difference is that it measures the surface area in square feet instead of square meters.

Foot-candles indicate how many lumens fall on a square foot of a surface. 

Often, bulb manufacturers use lux or foot-candles to explain how much light a bulb gives. 

Lighting professionals do the same when explaining how much light is needed to make a space suitable for a specific use.

They may say this space needs 50 foot-candles of light intensity. Or this bulb provides 500 lux.

So it helps to know how lux compares to foot-candles. 

We have 10.76 square feet in every square meter. Therefore, 1 foot-candle = 10.8 lux.

And so 50 foot-candles would be equal to 500 lux. And 5000 lux would be equal to 500 foot-candles.


Studying in the dark with light

Knowing a bulb’s lumen level makes it easy to tell whether it can produce enough light for a given space. 

Even better, knowing the lux helps you gauge how much of the light is landing on various spots in a given location.

To measure a bulb’s lux, you can use a light meter or an app. 

Light meters are readily available on the market and are easy to use.

Light meter apps are available for download, some at a fee, but most at no cost. The app uses your phone’s light sensor to calculate lumens.

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