How to Measure Brightness of Light Bulb

If you’re looking to buy a new light bulb, one of the factors you’ll want to consider is how bright the bulb is. But how do you measure brightness?


Measuring the brightness of light bulbs is easy and can be done with a simple device called a light meter.

In this blog post, we will show you how to measure brightness of light bulb using a light meter and provide some tips on choosing the right light bulb for your needs.

In addition, we will also provide some tips on choosing the right photometer for your needs. So, if you want to know how bright your light bulb is, keep reading!

Summary: Measuring the brightness of a light bulb is an essential factor when selecting appropriate lighting for your home or workspace. There are two main units used to quantify the brightness of a light bulb: lumens and foot-candles. Lumens indicate the total amount of visible light emitted by a light source, while foot-candles measure the amount of light reaching a specific surface area at a certain distance from the light source.

To measure the brightness of a light bulb in lumens, you can refer to the packaging or product specifications provided by the manufacturer. This information is typically listed on the box or in the product description online. For a more hands-on approach, you can use a light meter or a smartphone app with a built-in light sensor to measure the brightness in foot-candles.

Place the light meter or smartphone at a specific distance from the light source, usually one meter, and take a reading. To convert foot-candles to lumens, multiply the foot-candle reading by the surface area (in square feet) over which the light is distributed. This will give you an approximate measurement of the bulb’s brightness in lumens, allowing you to compare and select the most suitable light bulb for your needs.

Why Should You Measure Brightness of Light Bulb?

There are a few reasons you might want to measure the brightness of a light bulb. One reason is if you’re looking to buy a new light bulb and want to ensure it’s bright enough for your needs.

Another reason is if you have a light bulb that isn’t as bright as it used to be and want to know if it needs to be replaced. Whatever your reason, measuring a light bulb’s brightness can help ensure that you have the right light bulb for your needs.

Things to Consider Before Measuring Brightness of Light Bulb

Lumens Output

The lumens output is one of the most important things to consider when measuring brightness. Lumens measure the amount of light that is emitted by a light bulb. Therefore, the higher the lumens, the brighter the light bulb will be.


Another thing to consider is wattage. Wattage measures the amount of energy that is used by the light bulb. The higher the wattage, the brighter the light bulb will be.


However, a watt is actually a unit of power, not light. So, when you see a light bulb labeled “100 watts”, it does not mean it emits 100 lumens of light. A 100-watt light bulb only emits about 17 lumens of light.


Lux is a measure of how bright the light is. One lux is equal to one lumen per square meter. So, if you have a light bulb that emits 100 lumens of light and is shining on an area of 1 square meter, then the brightness would be 100 lux. Therefore, lux can be measured with a light meter.


Foot candles are another way of measuring the brightness of light bulbs. A foot-candle is the amount of light that falls on a square foot area from a distance of one foot. You can also use a light meter to measure foot candles.

Luminaire Efficacy

Luminaire efficacy measures how efficiently a light fixture converts energy into light. This is different from wattage because some light fixtures are more efficient at converting energy into light.

For example, a fluorescent light fixture is more efficient than an incandescent light fixture. Therefore, luminaire efficacy is measured in lumens per watt.


Candela is a measurement unit that defines a light’s brightness in a particular direction. A candela is equal to the light emitted by a candle in that direction.


The candela is mainly used when measuring powerful light sources like spotlights and headlights.

Now that you know the different ways of measuring brightness, you can choose the best one for your needs.

What You’ll Need

To measure the brightness of a light bulb, you’ll need the following:

  • A light meter
  • Black cloth with a box
  • A white sheet of paper or cardboard
  • A ruler or tape measure

Step by Step Guide: How to Measure Brightness of Light Bulb

Step 1: Prepare Your Work Area.

To get started, you’ll need to prepare your work area. First, clear the table or counter space where you can set up your light meter and materials.

Then, gather all of the materials you’ll need for the task. Finally, ensure you’ve all the items on the list above before proceeding to the next step.

Step 2: Take a Box.

Next, take a box and cut a hole in one side. The hole should be large enough to fit the light meter’s sensor and light bulb.


Make sure there are no other holes or openings in the box. As they can interfere with the accuracy of your measurements.

Step 3: Cover the Box.

After you’ve cut the hole in the box, cover it with black cloth. This will help ensure that only the light from the bulb enters the box and is measured.

Make sure you have wrapped inside the box fully with black cloth so no light can escape.

Step 4: Set Up the Light Meter.

Now, it’s time to set up your light meter. First, insert the batteries into the meter. Then, open the sensor cover and place the sensor inside the hole you cut in the box. Once the sensor is in place, close the cover.

Step 5: Place Your Light Bulb.

Now, it’s time to place your light bulb in the socket. Ensure the light bulb is screwed in tightly so it doesn’t come loose during the measurement process. Also, check that a black cloth covers the light bulb and light meter.

Step 6: Turn Off All the Lights in the Room.

To get an accurate measurement, you’ll need to turn off all the lights in the room. This includes overhead lights, lamps, and any other light sources.


Once all the lights are off, close the curtains or blinds to block out any light coming from outside. The goal here is to make the room as dark as possible.

Step 7: Set the Light Meter to the Correct Setting.

Now, it’s time to set the light meter correctly. For most light meters, you’ll want to set it to “foot-candle” or “lux.”

These settings will measure the amount of light in a given area. Once you’ve set the light meter to the correct setting, press the “on” button.

Step 8: Place the White Sheet of Paper.

Now, take the white paper and place it under the light bulb. The purpose of the white sheet is to reflect light back up to the sensor. This will help ensure that the light meter gets an accurate reading.

Step 9: Take the Measurement.

Once the white sheet is in place, you can take the measurement. Hold the light meter close to the light bulb and press the “measure” button.

The light meter will then give you a reading of the light bulb’s brightness. You’ll want to take multiple measurements and average them together to get the most accurate reading.

Step 10: Record the Results.

Once you have your measurement, it’s important to record the results. This way, you can refer back to them later if needed.


You can record the results in a notebook or on paper. If possible, take a picture of the light bulb and the light meter, so you have a visual reference.

Tips for Measuring Brightness:

There are a few things you can do to ensure accurate measurements:

1. Calibrate your light meter regularly. This will help ensure that your readings are accurate.

Make sure the room is dark when taking measurements. Light interference can significantly impact the readings.

2. Use a diffuser when measuring brightness. This will help spread the light evenly and prevent hot spots.

3. Take multiple measurements and average them together. This will help account for any slight variations in the readings.

4. Use the lux setting on your light meter. This measures the amount of light in a given area and is more accurate in measuring brightness than using the wattage setting.

5. When taking measurements, it is important to remember that the human eye is not equally sensitive to all wavelengths of light. Therefore, two light bulbs with the same lux rating can appear to have different brightness levels.

Final Words

Measurement of light bulb brightness is an important aspect of lighting design and engineering. By understanding how to measure the brightness of a light bulb, you can ensure that your lighting fixtures provide the correct amount of illumination for the intended space.

There are various methods for measuring a light bulb’s brightness, each with its advantages and disadvantages. Measuring the brightness of a light bulb can be done using a simple device called a lux meter.

A lux meter measures how much luminous flux is shining on a surface per unit area. In this blog post, we have discussed how to measure brightness of light bulb with a lux meter and provide some examples of readings taken with different types of bulbs.

We hope this guide has been helpful for you. If you have any questions or want to know more, feel free to comment below!

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