In the areas where too little or too much light can cause serious damage, or where a limited range of illuminance leads to optimal results, the use of stationary photometers is recommended. Photometers for mobile or stationary measurementsД¬hecking the lighting of workplaces and traffic routes is usually done with mobile devices. Often they show the color distribution also graphically on a color display.

Many of these photometers not only display numerical values for the respective primary colors. The values are then specified, for example, as X, Y and Z values according to the CIE-XYZ color space or as red, green and blue values according to the CIE-RGB color space. The colorimetric values can be specified as three primary colors in three-part additive color models. Some photometers for illumination measurement do not only register the illuminance but also the color coordinates of the incident light. For this purpose, the International Commission on Illumination (CIE) defined the light efficiencies of different wavelengths for the eye of a normal observer adapted to bright and dark. For the measurements of the illumination of living and working areas, the spectral sensitivity of the photodiode should be adapted to the brightness sensitivity of the human eye.

These devices can measure the illuminance for these types of light more accurately than those from other light sources. In addition, an attention should be paid that some photometers with their sensor and the corresponding filter are designed for certain light sources.

If these measurement deviations have a strong effect on your application, it is better to choose a device with the better resolution. The measuring accuracy of many devices is 3 or 5 percent of the measured value. For indoor measurements, a measuring range of 2,000 lux or 10,000 lux is generally sufficient for outdoor daylight measurements, the measuring range should be 100,000 lux or higher. For the evaluation of the necessary measuring range it is important to clarify whether only minimum values should be checked with the photometer or whether high daylight values must also be recorded for certain evaluations. In clear weather, natural daylight reaches much higher values than required for visual tasks and most technical and natural processes. One lux corresponds to one lumen per square meter. The illuminance is a surface-dependent value that indicates how much luminous flux is incident on a surface. Compliance with these values for illuminance is measured in lux at the level relevant to the use, for desks or workbenches, which means on the table surface, for wall boards on the board surface and for traffic routes on their surface. In occupational safety guidelines, accident prevention regulations and technical standards, a minimum brightness value is prescribed or recommended for many areas. Light also plays a decisive role in the development and growth of plants and the durability of certain substances. This applies equally to stay in private and public areas. Situation-specific lighting is therefore important for recognizing dangerous situations and increases the ability to concentrate on work and learning tasks. Selection criteria for a photometer for measuring illuminanceДЇor the human eye, capturing details, colors and spatial structures is more difficult in increasing darkness. The selection criteria for a photometer depend primarily on whether it is to be used for measuring the illuminance or as a measuring instrument for determining the properties of liquids. These instruments, which are equipped with special sample containers, are also called turbidity meters. However, the photometers can also be used to determine the proportion of foreign substances or the concentration of the known mixtures of substances via the attenuation the light intensity. Based on the unit of illuminance, the photometers that are only used for this purpose are also called luxmeters. Photometers are basically used to measure illuminance.

Water quality measuring instruments