Convert lux to lumens and the lumens per watt concept

Lumen is a unit of measurement used to describe how much visible light a source emits and is always present on lamp boxes. The better light bulb is one that uses less electricity while producing more light. LED lamps have a higher position than older incandescent bulbs since they require less power to provide greater light. Now, when comparing similar-powered LED light bulbs, the one that emits more light has better LEDs in it.

Now, in order to measure lumens, we require a tool called an integrating sphere (also known as an Ulbricht sphere), which is both large and expensive. We need a watt meter in addition to measuring lumens to determine the lamp’s power. Lumens per watt is derived by dividing these two figures. It refers to the amount of light this light bulb produces per watt. We can compare a 20-watt lamp from one brand with a 10-watt lamp from another brand using this number because we are aware of how much light each watt in each company’s light bulb produces.

There are two different units, lux and lumen, which are used to measure visible light.

Definition of lux from Wikipedia:

The lux (symbol: lx) is the unit of illuminance, or luminous flux per unit area, in the International System of Units (SI). It is equal to one lumen per square metre.

Lumen definition from Wikipedia:

The lumen (symbol: lm) is the unit of luminous flux, a measure of the total quantity of visible light emitted by a source per unit of time, in the International System of Units (SI).

These two definitions demonstrate how distinct these two units are; however, the definition of lux also states that lux and lumen can be equal if all the light from the source or lamp is concentrated on a one-meter square.

Watch the video below to understand the rest of the story, but if it’s difficult, for you Read more:

We have a “sphere” of light because it is difficult to cast the lamp’s light precisely and fully without any waste or reflection back onto a square. Wherever we set our lux meter on the surface of the sphere, the lux number is equal to lumens if we place the lamp within the sphere, and the area of the sphere is equal to one square meter.

If we set S to one, the radius produced is equivalent to 28.20 cm using the sphere’s area formula, which is equal to S = 4(Pi)r2. That is, the lux measurement obtained at a distance of 28.2 cm from the light source is equivalent to lumens!

Of course, this approach is flawed and completely inaccurate. For instance, the setting must be absolutely dark to ensure that no distracting light interferes with the test. Or the area should be absolutely dark to prevent light reflection from anywhere.
For instance, if you look at the comments on the same video, several people suggest ways to improve the accuracy of this measurement. There are two other methods: DIY Sphere and pipe tube. If you click on the links and read about them, the pipe technique is simpler but has just positive error, which may not be significant given the approach’s low cost.