The unit of measurement of light. How to measure.

unit of measurement of light

The unit of measure of light is Lumen.

The unit of measure of light is – Lumen. This is the unit of light flux in the system of units of physical quantities – SI. 1 Lumen = light flux, which is emitted from a point isotropic source. The luminous intensity of the light must be 1 candela. Total luminous flux emitted from isotropic luminaire, with light intensity 1 candela, is equal to 4 lumens.

Lumen is the total luminous flux from the luminaire. Despite this, this unit of measurement is not very common because it does not take into account the concentrating efficiency of a reflective object or lens. Lumen is not a direct measure of luminance or lantern performance. A wide beam of light can take the same values as a narrow beam. Lumens is not capable of determining light intensity because estimating in lumens involves taking into account all diffuse light, which is useless in this case.

Unit of measure of luminous intensity – Candela

The unit of measure of light intensity is the candela. It is referred to as Kd or cd. Candela is equal to the luminous intensity, which is emitted in a certain vector, given by the source of monochromatic emitter with frequency 540×10 to the 12th degree of Hertz.

The SI system has 7 major units of measurement, one of which is the candela. Candela is equal to the luminous intensity emitted in a particular vector given by a source of a monochromatic emitter with a frequency of 540×10 to the power of 12 Hertz. Its energy power of light is 1/683 (W/sr). Cp is a steradian, which is used to measure solid angles. In Slavic countries it is referred to as Cp, but the international designation is sr.

unit of measurement of light

The mentioned frequency corresponds to the green spectrum. The human eye is more sensitive to green than to other colors. To achieve the same light intensity with a different frequency, higher energy intensities are needed.

Scientists of past centuries defined Candela as the power of light emitted from a black object perpendicular to a plane of 1/60 square centimeters at a temperature of 2042.5K. At this temperature, platinum melts. Modern science has defined 1/683 so that the present designation corresponds to the previous one.

A candle flame emits about one candela of light intensity. Because a candle is called candela in Latin and candle in English, this unit of measure was formerly called that: candle. Now this name is not used and is considered an archaism.

The unit of measurement of illumination.

The unit of illuminance – the ratio of luminescence to the surface that it illuminates, is commonly referred to as illuminance. It takes into account the perpendicular incidence of light on a particular plane.

The unit of measurement of illuminance is Lux (lux.).

1 lux = ratio of 1 lumen to 1 meter of surface per square meter.

Luminous flux is measured in lumens. Both units are listed in the International System of Units. In the United Kingdom and the United States, light levels are recognized in lumens per square foot, also called foot-candela. Luminance is the illuminance from a 1-candela source at one foot from the illuminated plane.

Is it really necessary to measure the degree of illumination and what is the unit of light?

Scientists have proven that light that is too dim or too bright destroys the retina of the human eye, causing visual acuity to deteriorate. Because of the destruction of the retina, the speed and quality of brain function decreases. Lack of brightness increases drowsiness in people, reduces performance and worsens mood. It should be taken into account that we do not take into account situations in which a dim glow decorates the environment: a romantic date, watching a movie and so on. A saturated flow of light adds strength, energy, desire to work, thereby fatiguing the person faster.

Measurements are made to determine not only the degree of illumination, but also the level of noise, dust, pollution and vibration. According to doctors, the constant lack of light in the workplace leads to fatigue of employees, deterioration of vision and concentration. Workers become less able to work, which can lead to accidents due to inattention or other reasons.

In addition to people, other living organisms suffer from insufficient light: plants, animals. For rapid development and fertile flowering plants definitely need a strong stream of light. Animals due to poor lighting can have disorders in growth and development, reproductive function, weight gain, and may decrease the activity of the creature.

What is lighting like?

Lighting is usually natural and artificial.

Natural sources of light:

  • the sun;
  • the moon;
  • the diffused light of the firmament;
  • comets;
  • aurora borealis;
  • electrical discharges in the atmosphere;
  • stars and other celestial objects.

Artificial sources:

  • various illuminating forms and designs;
  • lamps;
  • luminaires;
  • flashlights;
  • monitors;
  • television sets;
  • cell phones and others.

Light intensity

The unit of measure of light intensity is measured when setting up lighting in a room or when preparing a camera to take pictures. Experienced photographers and lighting professionals use digital exposure meters, but you can also make a simple device with a similar principle of their own hands.

Many devices are designed for a particular type of lighting. For example, measuring the glow of sodium lamps, you will achieve a more accurate result than performing calculations over an incandescent lamp.

You can install an app on your smartphone that will determine the intensity of the light. No matter how good your phone and the app you choose, the results will be skewed and inaccurate, so it is better to use a specialized device.

Most devices measure light intensity in lux, since that’s the accepted unit, but some are set up to display footcandles.

How do they measure the degree of illumination

As we have already found out, the unit of measurement of illumination is Lux. It’s not hard to guess the name of the instrument used to measure light levels. “Lux” plus “meter” (from the ancient Greek translates as “measure”, “meter”) equals a luxmeter. The principle of operation of this portable device is similar to that of a photometer.

The light flux falling on the element releases electrons in the body of the semiconductor, which causes the electric current to be conducted by the photocell. The value of the electric current is directly proportional to the degree of illumination of the photocell, which is displayed on a scale or on an electronic display if it is a modern model of the luxmeter. Analogue instruments are equipped with a special scale with degrees. The movement of the arrow determines the final results of measurements.

Digital devices.

Analogue luxmeters were replaced by digital ones – small computers. The parameters can be seen on a small LCD screen. The part used to measure light is often contained in an outer case and connected to the main device by a flexible wire. Because of this design, you can measure light in any location, even hard-to-reach places. According to GOST, the error of the device should not exceed 10 percent.

Important points.

When calculating the comparative light intensity, you can make a measurement of the intensity of lighting with an analog or digital device. Modern meters display parameters in lux, while the outdated analog ones – the ones with an arrow – in footcandles. One footcandela equals 10.76 lux.

So we have understood what illuminance, light intensity and light intensity mean. You have learned what the units of measurement of luminous flux are, measuring instruments, you got acquainted with the standards and recommendations. Now you have a basic knowledge of lighting and will not be confused if you hear the word “candela” or “luxmeter” in a conversation. If interested, you can buy a measuring device and make some measurements of the illumination of your workplace. Then you will know whether your lighting complies with the standards or not.