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What measures describe light?

What measures describe light?

Light plays a key role in our lives. It allows us to see the world around us. However, we don’t always realize that light is a complex physical phenomenon that can be described using many different measures and units. In this article, we will look at the most important measures used to describe light, such as candela or cd/m2.

Luminance – candela

One of the basic measures of light is Luminance, also referred to as screen brightness. It is expressed in candelas per square meter (cd/m2). The candela, the SI unit of light intensity, is key in this context. Luminance tells us how bright an object or surface is. The higher the luminance value, the brighter the observed object.

Luminance is crucial in the design of various display devices, such as monitors, TVs, screens, digital displays, etc. For example, a typical computer monitor should have a luminance in the range of approx. 140-250 cd/m2, while a display intended for outdoor use should have a luminance of at least 1000 cd/m2. Screen brightness and cd/m2 are the key parameters here.

When designing display devices, it is very important to match the luminance to the brightness of the environment in which the display will operate. Too low a screen brightness in a bright environment will make the content on the screen unreadable. On the other hand, too much screen brightness in a dark room can tire the eyes and impede perception. Therefore, location and lighting conditions should always be taken into account when selecting a display.

For example, LCD displays installed in shopping malls should have a luminance of 500-750 cd/m2. Office monitors, on the other hand, only need to provide 150-300 cd/m2. Screen brightness and cd/m2 are also key here. It’s even different for in-vehicle displays – here you need luminances of 1,000 cd/m2 or more. Only then will the content be clearly visible regardless of the lighting conditions outside the vehicle.

Interestingly, looking through the technical data of smartphones, you can see that the higher-end models offer luminance even over 700 cd/m2. This is to ensure good readability of the display even in very bright conditions, such as in full sunlight. Cheaper smartphones, on the other hand, have to settle for a luminance of 300-500 cd/m2.

In summary, luminance is a key parameter of any electronic display. Its proper selection determines the readability and comfort of the device. The manufacturer, which offers a wide range of LCD displays with different luminance levels, is able to meet the needs of a variety of customers and applications.

Light intensity – lux

Another important measure of lightis light intensity, defined in lux (lx). One lux is the intensity of light falling on an area of 1 m2 from a light source of 1 lumen. In other words, light intensity tells us the amount of luminous flux falling on a given surface.

Light intensity is crucial when designing interior lighting. For example, a typical office should be illuminated with light of 300-500 lux, precision operations require 1000-2000 lux, and simple warehouse work even only 100 lux.

Properly designing the lighting in a room or space requires an in-depth analysis of what activities will be performed in it. A different light intensity will be required in a hospital operating room, where very bright light is needed to enable precise procedures, and another in an office, where the most important thing is to have a good view of documents and monitors, but without blinding employees.

Still another example would be production halls, where the light should enable efficient and safe work, but at the same time not tire the eyes during long hours of activity. In stores, on the other hand, lighting should display merchandise and encourage shopping. So you can see that choosing the right intensity and type of lighting depends on the specific purpose of the space.

Light – candela

Luminosity is a measure of the power of light radiation emitted by a light source in a specific direction. The SI unit of luminosity is the candela (cd). Luminosity allows comparing the power of different light sources. For example, a typical incandescent bulb has a luminous intensity of approx. 10-20 cd, LED lamp – approx. 100 cd, and a professional spotlight up to 100,000 cd.

Luminosity is an important feature of lamps and luminaires. By comparing the luminosity of different models, we are able to choose the ones best suited for a given application. The high luminosity lamp will be a good solution for lighting large areas, such as yards, parking lots, production halls. On the other hand, a lamp with low luminosity will work better as a spot light for a desk at home or a reading room in a library.

It is also worth noting that, in addition to luminosity, the angle of the lamp is also important. The wide angle will allow to illuminate a large area with diffused light. A narrow angle will focus the light beam and allow to illuminate a selected surface or object more strongly. For this reason, spotlights with high luminosity and a narrow angle are often used to illuminate monuments, memorials or architectural features.

Light efficiency

To compare different light sources, in addition to luminosity, another measure is needed – luminous efficacy. It determines the ratio of the luminous flux emitted by the light source to the electrical power it consumes. The unit of luminous efficiency is lumens per watt (lm/W).

Luminous efficacy assesses how efficiently a light source converts electricity into light. For example, a typical incandescent bulb has an efficiency of approx. 15 lm/W, fluorescent lamp – 50-100 lm/W, and LED even more than 150 lm/W. Therefore, LED lamps are gradually displacing older technologies.

In an era of rising electricity prices and greater environmental awareness, more and more attention is being paid to the energy efficiency of lighting. That’s why more and more LED lamps are appearing on the market with record high efficacy reaching up to 200 lm/W. In addition, manufacturers are constantly improving LED technology, so that the latest LED lamps are able to provide the same amount of light as older technologies, using up to 4-5 times less electricity!

High luminous efficiency also means less heat emission from the lamp. As a result, smaller heat sinks are required to cool them, allowing LED lamps to be constructed in increasingly smaller sizes. This is especially important in lamps designed to be built into furniture, bookcases, light bars, etc. In summary, luminous efficacy, along with other parameters such as longevity and color temperature, makes it possible to fully assess the properties of a given light source and select the optimal solution for your needs.

Color temperature

The color temperature of the light is A measure of the color of the light they emit. It is defined in kelvins (K). The higher the color temperature of the light, the bluer its color. Candlelight, for example, has a temperature of approx. 1900 K, typical incandescent bulbs approx. 2700 K, fluorescent lamps 3000-6000 K, and sunlight as much as approx. 5500 K.

Proper selection of the color temperature of light sources is important in many applications, such as lighting offices, stores, hospitals and operating rooms. A color temperature that is too low can cause drowsiness and decreased productivity. In contrast, too high a temperature can cause visual fatigue and irritability.

For example, lamps with cool white light above 5,000 K are recommended for lighting office spaces, doctors’ offices, workshops requiring precision. Warmer shades of 3000-4000 K will work well in bedrooms, living rooms, reading rooms – anywhere a more cozy, homey mood is desired.

The color temperature also determines the color rendering of illuminated objects and spaces. Cool light will better reflect blue-green colors, while warm light will reflect red-orange colors. That’s why warm lamps are often used in clothing stores to highlight the colors of clothes. On the other hand, in vegetable gardens it is better to present vegetables and fruits in a light closer to daylight.

In summary, the color temperature of light significantly affects the ambience and functionality of lit rooms and color perception. Its conscious choice allows you to create a space optimally adapted to its purpose and the preferences of its users.

Light color

In addition to color temperature, light is also characterized by color. There is a distinction between white light and light of a particular color, such as red, green, blue. Light color is important in many fields, such as medical diagnostics, traffic signals and lighting plants in greenhouses.

The ability to fine-tune the color of the light allows for many interesting and useful applications. For example, germicidal lamps use blue light of a certain wavelength to destroy bacteria and microorganisms. In medicine, in turn, lamps with red or infrared light are used to treat skin diseases.

In agriculture, controlled light color helps control plant growth, flowering, fruiting. For example, alternating red and blue lamps in greenhouses accelerates tomato growth. On the other hand, the red light of LED lamps helps strawberries grow faster.

In our homes, too, we are increasingly using color-changing lighting to create mood and functionality in interiors. The warm white light of the lamps dimmed in the evening helps you relax and unwind before bed. Cool white light in the morning stimulates the body and improves concentration.

The ability to seamlessly change the color from white to any shade of RGB allows you to get millions of combinations and completely change the character of the room with the help of lighting. As a result, RGB LED lamps and strips, which we can control from a remote control, app or smart home system, are becoming increasingly popular.

Read more about smart spaces in our range of displays for smart home, smart office and smart city.

As you can see, light color is another important parameter, besides intensity and temperature, to fine-tune lighting to meet the expectations and needs of users in a given application. Technological advances are giving us more and more options and control over this aspect of lighting.

What is light measured by?

A number of instruments, such as lux meters, colorimeters, spectrometers and gonioradiometers, are used to measure light parameters. These devices use light sensors, usually photodiodes, photoresistors or photomultipliers. They allow you to accurately measure the intensity, color and other characteristics of light from both light sources and illuminated objects.

Lux meter

A lux meter is used to measure illuminance, or the amount of light falling on a given surface. Allows you to control whether the lighting parameters in a room, office, production hall, etc. meet the required standards. The colorimeter measures the color of light, including its temperature and deviation from the standard scale. With its help, you can check whether the parameters of the light emitted by LED lamps are in accordance with the manufacturer’s specifications.


The spectrometer analyzes the exact spectral distribution of light, that is, its components at different wavelengths in the visible range as well as in the infrared and ultraviolet. These advanced devices are used, among other things. in laboratories to precisely study the properties of light sources, lasers or other optical phenomena.

In summary, the development of measurement techniques makes it possible to increasingly accurately analyze and control light parameters in scientific research, industry and everyday life. This allows lighting to be optimized for energy savings, functionality and user safety.


As you can see, light is an extremely complex physical phenomenon with many parameters. Each has a different role and allows us to characterize differently how a given light source interacts with the illuminated surface or observer.

Luminance determines the brightness of the screen and the light emitted. The intensity indicates how much light falls on a unit area, often expressed in cd/m2 – sometimes incorrectly written as cd m2. The candela is a unit of luminosity and tells the power of a light source. The candela unit is used in the SI system. Luminous efficacy shows how efficiently energy is converted into light. Color temperature and hue characterize the spectrum and color of light.

Understanding these basic parameters and being able to use the appropriate metrics is crucial for engineers and professionals involved in lighting design. They make it possible to precisely define the requirements for lighting systems in a variety of applications – from offices and factories to hospitals or shopping malls. This knowledge is also useful for any of us who want to consciously shape the lighting of our apartment or house.

It is also essential knowledge for a display manufacturer such as Unisystem.

We hope that this article has helped to introduce and better understand the basics of light metrology. He clearly demonstrated that proper selection of light parameters is crucial to the functionality, performance and safety of any displays and lighting systems around us.


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