How is lumens measured from a light

Plus, we'll show you how lumens are measured, an easy way to translate watts to lumens and why all these changes are a good thing. But what are lumens, exactly? And how do you understand what are lumens in light bulbs and light fixtures? In addition to being the Internet's premier modern lighting and design store hey, that's us!

And if you want a fixture with bright, luminous personality, it's the key to choosing the perfect piece for your lighting scheme. And watts do not. Not that watts are bad, but they measure energy use, not light output. With new, energy-efficient LED technology, we can no longer rely upon wattage to indicate how bright a bulb is.

See how to measure lumens below:. Use the chart above to determine exactly how many lumens are in a watt and vice versa. This should provide you with a good understanding of how bright lumens is vs. Additionally, you can use the color temperature chart to help you in choosing the best lighting for your application - whether it's for kitchen or bedroom lighting , or perfecting your pendant lighting. Kelvin, lumens, watts, oh my! The changes in lighting regulations and technologies mean that there are new lighting terms to learn.

For example, while we've previously looked to watts to learn a bulb's brightness, that information is now presented in lumens. Newer bulbs have a Lighting Facts label that will give you all the details of a particular bulb similar to a nutrition label on food :.

Concerned about this significant waste of energy, the federal government set out to change regulations on light bulbs, requiring them to be more efficient. These federal regulations first applied to watt incandescents in and watt bulbs in In , incandescent and watt bulbs began to be regulated in the same way. So, it's not that incandescent bulbs are going away—they are simply changing. Plus, there are still many incandescent bulbs that are exempt from these regulations.

Three-way bulbs often used in table and floor lamps , colored lights and appliance bulbs are all staying the same. There are serious, measurable benefits to these changes. The U. Thankfully, the more energy efficient light bulbs primarily halogen, compact fluorescent, LED now on the market are available in an amazing array of sizes, colors and shapes.

Your gift will appear in your cart. One gift per customer, while supplies last. Lumens reserves the right to substitute an item of comparable value. Some eligible brands may include items that do not qualify for this promotion. So basically, if you need a light bulb that emits light in all directions for example ceiling light in a house look at lumens when comparing various bulbs, however, if you need a light that can focus the maximum amount of brightness in a smaller beam such as a spot light or a flashlight, look at candelas when comparing such lights.

Besides these two, illuminance is also an important metric, measuring the amount of light falling on a given surface measured in lux or foot-candles , but later with this. The classical example of explaining lumens and candelas: Imagine that you place a transparent sphere with 1 meter radius over a candle.

The candle produces light intensity of 1 candela and emits light uniformly in all directions. If you cut a 1 square meter large hole in the sphere, 1 lumen of light would come out of that hole. This gives as an equation:. We can also calculate the luminous flux of entire sphere using the same equation. To do this, first we need to know the surface area of the sphere , this can be calculated using a formula:.

The same equation can be transformed to calculate candelas :. Lets look at a new example, we have a light bulb that emits lumens of light uniformly in all directions, with the same transparent sphere with 1m radius over the bulb. But if we want to calculate the light intensity in a certain direction, lets say passing through one steradian as in the first example, we can use the same formula:.

To even better illustrate the difference between luminous flux lumens and luminous intensity candelas , imagine a light bulb that produces 1 candela or 12,57 lumens, if you cover one side of the bulb it will still produce the same light intensity of 1 candela, but half the luminous flux — 6,28lm. But because lumens measure the total amount of visible light from the source, covering half of the bulb will decrease the total amount of visible light by half.

This is why you should compare candelas when purchasing a spot light or flashlight with concentrated light beam and lumens or lux when purchasing indoor lighting such as ceiling lights or outdoor flood lighting. These previous calculations and formulas were mostly attributable to a light source that is isotropic or in other words, emits light uniformly to all directions.

Now lets look how to calculate candelas and lumens in light bulbs at certain angles. In previous examples we calculated lumens and candles assuming that light is emitted uniformly to all directions or in one example through a solid angle of one steradian, where 1 lumen equaled 1 candela , but usually we purchase lighting fixtures that illuminates light in a certain angle, spot lights illuminate in a narrower angle to provide more focused beam while flood lights illuminate in a wider angle to cover larger surface area.

And in opposite, if we decrease the luminous intensity candelas , we should increase the viewing angle steradians to produce the same luminous flux lumens. So we can say that luminous intensity is inversely proportional to the viewing angle, meaning that increasing one value at the same rate, the other will decrease.

At the same time when calculating luminous flux, if we increase either the luminous intensity or the viewing angle, the luminous flux will increase, and in opposite, if we decrease either the luminous intensity or the viewing angle, the luminous flux will also decrease.

So how can we determine this apex angle of a light beam? The full equation to calculate luminous flux lumens of a light source, if we know luminous intensity candelas and apex angle steradians is:. To calculate luminous intensity candelas , if luminous flux lumens and apex angle steradians are known, use this equation:.

Now lets check this equation on a more practical example. We can use the previous equation:. So it is true, if we increase the apex angle of a lamp while keeping the luminous intensity the same, the lumen output will also increase. Now the lamp should produce less lumens:. To summarise, luminous flux measures the total amount of visible light emitted in all directions, the unit of luminous flux is lumen lm. Luminous intensity measures the quantity of visible light emitted in a given direction at solid angle by a light source, the unit of luminous intensity is candela cd.

Candelas are mostly used to describe brightness of lighting fixtures that produce focused beam of light at a narrower angle in a single direction, such as laser pointer, flashlight and spot light. Lumens are used to compare bulbs or lighting fixtures that illuminate in a wide angle and need to produce light equally in all directions, such as ceiling lights and some types of food lights. Generally, wider the beam angle of the light, lower the light intensity, and narrower the beam angle of the light, higher the light intensity.

Illuminance is the amount of light or luminous flux falling on a surface. Illuminance is measured in lux lumens per square meter or foot-candles lumens per square foot using the US and British metrics. Illuminance is independent of type of the surface it illuminates on and only depends on the amount of light that falls on that surface, so it will be the same either when illuminating on a wall, ground, floor, tree or any other object.

Illuminance in opposite to lumens and other lighting metrics can be easily measured with a simple device called a light meter, or even with a smartphone that has a special application installed. Definition of lux — lux lx is a measuring unit of illuminance, lux measures luminous flux per unit area or how much light is falling on a given surface. Basically, lux will determine how bright the surface illuminated is going to be.

One lux equals one lumen per square meter of surface area:. In the Imperial and US customary measurement systems , a term foot-candle fc is used instead of lux. Foot-candle also measures the amount of light falling on a surface, but instead of lumens per square meter used to measure lux , lumens per square foot are used to measure foot-candle.

Foot-candle is the most widespread lighting measurement in the industry. The explanation for this choice dates back to the origins of the candle itself. When people began to measure the intensity of light, candles were the most common light source available. At that time, the candle-making industry provided a consistent, steady, clean, and efficient way to measure light. Thus, we use this well-known expression, even to this day. The lumen is a significant entity: it measures the total amount of visible light emitted by a given source.

All other measurements are based on the lumen. The lumen measurement originated from the basic concept of foot-candles. It might be illustrated, more or less, by the image shown here. A more scientific definition exists today, but this drawing helps visualize the lumen. Picture a candle set in the middle of a sphere measuring 0. If we cut a hole that measures 0. A foot-candle equals one lumen per square foot. This is a British measurement.