When we choose a light, there are several performance indicators we should focus on. For example, the brightness of the light, the duration of the light, and the weight.
However, when we actually try to select a light, many questions arise about the light’s specifications.

• There are several lights that claim “800 lumens” in their catalogs, but do they all have the same brightness?
• How many hours does the light last in actual operation?
• Even if the light is bright and lasts for a long time, is it heavy and difficult to handle?

In this blog, we measure the lumens (total luminous flux), lighting time, and weight of lights using measurement equipment.
Based on the results, we provide the following information

Measured Lighting Time
Measured Average Lumens
Measured Total Lumen Output
Measured Lumen-to-Weight Ratio (LWR)

These indicators are calculated using this site’s original method.
You can use this information when selecting a light.

Why do we use our own performance indicators?

Most nominal lumen values provided by light manufacturers are the amount of light immediately after the light is turned on.
But the nominal lumen value has a drawback. The nominal lumen value does not take into account the fact that the brightness of a light dims as it is continuously turned on.

Therefore, we calculate the average lumens during the lighting time and the total lumen output generated during the lighting time.

Lumen Weight Ratio (LWR) is calculated as a performance index that also considers the actual weight of the light.

Measured Initial lumen

Initial lumen is the lumen (total luminous flux) of the light immediately after it is turned on (30 to 120 seconds later).
This is based on the ANSI/PLATO FL1 Standard, a performance evaluation standard for portable lights.

Most of flashlights’ nominal lumen values are the luminous flux at the beginning of lighting.
However, most lights are brightest just after they are turned on. As time goes by, they become dimmer.
For this reason, I don’t emphasize the initial lumen as an indicator of the light intensity of a flashlight.

Measured Lighting time

This is the time it takes for the light to reach 10% of its initial lumen after it is turned on.
The ANSI/PLATO FL1 Standard measurement method is also used for this.

Why do we use “until the light reaches 10% of the initial lumen” instead of “until the light turns off”?
The reason for this is to exclude the time when the light remains on at a light intensity that is not practical.

Measured Average lumens

This is the average lumens during the lighting time.

A light that is bright only immediately after it is turned on may have its initial lumen value listed in the catalog specifications. After the first boost, the light may be rapidly dimmed to extend the lighting time.
This average lumen value can be low for such lights.

Measured Total Lumen Output

This is the cumulative light output generated by the light during its lighting time.
The higher the lumen output of the light and the longer it is on, the higher the total lumen output.
It corresponds to the yellow area in the graph below.

Suppose we have a light that provides 100 lumens for 10 hours.
Its total lumen output would be 1000 (= 100 lumens * 10 hours).

Also, total lumen output = average lumens * lighting time.

Note that total lumen output is a term unique to this site. It is not used in other places.

Measured Lumen-to-Weight Ratio (LWR)

Lumen-to-Weight Ratio (LWR) is the total lumen output divided by the actual weight of the light (grams including fixtures and batteries).
I consider LWR to be a definitive indicator in determining the performance of a light.

For example, a light with a total output of 1000 lumens and a weight of 100 g would have an LWR of 10.0.

A heavier light will have a smaller LWR.
Light output can easily be increased by combining a high-power light with a high-output battery. But it will be a heavy light.
Imagine what would happen if an automobile battery and light were mounted on a bicycle. It would be too heavy to pedal very nimbly.

With the LWR, you can find a light that is bright for its weight.

Conclusion

Based on the actual measurements of the lights, I provide the following information.

• Measured Lighting Time
  Time it takes for the light to reach 10% of its initial lumen just after it is turned on
  
• Measured Average Lumen
  Average lumens during the lighting time
  
• Measured Total Lumen Output
  Cumulative amount of light produced by a light during the lighting time
  
• Measured Lumen-to-Weight Ratio (LWR)
  Lumen output divided by the light’s measured weight (grams including fixtures and batteries)
  

This information can be used as a reference for your light selection.

The post Explanation of useful indicators for light selection, “Average Lumens”, “Total Lumen Output”, and “LWR” appeared first on Digital Bike Parts.

I’ll show you how I measure lumens of lights below.

It’s not easy to measure total quantity of visible light

It is easy to measure the illuminance of a light at a single pinpoint.

The illuminance of a particular point can be measured easily with an illuminance meter like this one shown below.
This is the EM-9300SD measuring instrument I purchased in 2016.

However, a light illuminates a large area rather than a single point.

Now we are measuring the illuminance of two lights.
Suppose that their measured illuminance at a center illuminated point are the same.
In this case, the light with the larger illuminating area is judged to be brighter overall.

Then, how should we measure the total quantity of visible light emitted by those lighting devices?
One possible method is to place light-measuring sensors in multiple locations.

However, each light can have different illuminated area.
Even if the measurement results are obtained at multiple points, it is not easy to determine how to relate them to the total light quantity.

In addition, slight differences in distance and the orientation of the light sensor can significantly change the measured light intensity.

Thus, it is difficult to measure the total light quantity with this kind of illuminance meter

Measuring lumens (total luminous flux) with an integrating sphere

I use an integrating sphere to measure the total luminous flux (total luminous flux = lumens) of a light.

Integrating sphere is used to measure lumens. When light is illuminated in a sphere, the inside of the sphere is filled with a homogeneous brightness due to the reflection of light within the sphere.

With a sensor in the sphere, the light lumen value can be measured.

This is the integrating sphere. It’s a hollow steel sphere with a diameter of 50 cm (about 1.64 feet).

The inner surface of the integrating sphere is coated with highly reflective barium sulfate.

A measuring device called a “spectral luminous flux analyzer” is connected to the integrating sphere to measure lumens.

For Correct Measurement

Even when using an integrating sphere, changes in measurement conditions can cause deviations in lumen values.
To avoid deviations in the measured values, I make several efforts as shown below.

• The mounting position and angle of the light and the measurement device should be constant. (See (Remarks))
• The performance of lights and batteries is greatly affected by temperature. Therefore, I keep the room temperature between 20℃ (68℉) and 25℃ (77℉).
• Use new, I use charged batteries.
  As a rule, I use lights and batteries that have not been used for cycling.
• For alkaline battery-powered lights, I use batteries of the same brand, with a new production date and unused.
  

(Remarks) Placement of lights on the integrating sphere

According to the instructions attached with the integrating sphere, lights can be placed either “outside the sphere” or “inside the sphere” as shown in the figure below.
However, in practice, if the light is placed inside the sphere, the exterior of the light itself will absorb light.
Therefore, depending on the size and color of the light, the lumen measured will vary.
In particular, a lighting device with a black exterior absorbs light itself, resulting in lower measured lumens.

When I measure lumens, a lighting device is placed outside the sphere and light is irradiated into the sphere.
If the light is placed on the outside, it is necessary to take measures to shield the light.
A hole must be prepared to match the shape of the light. In fact, this process is quite time-consuming.

The analyzer is calibrated with a reference bulb provided by the measurement device manufacturer.
The following is a reference bulb. It has been verified in advance that it emits a certain lumen of light when a specific electric current value is applied, and the analyzer is calibrated with that light.

The post How to measure lumens of a light with an integrating sphere appeared first on Digital Bike Parts.