Technical insights on LEDs

Lux and Lumen

Lux and Lumen are two different measures of the luminous flux, Lumen is a measure of the "quantity of light" emitted by the source, Lux is a measure relating to the illuminated area. Often in the description of LED luminaires there is (deliberately?) Confusion between these two terms, giving excessive emphasis to the value in Lumen which in reality expresses only the amount of light emitted by the LED chip without taking into account the other elements that make up a luminaire. lighting such as parabola, lenses, diffuser, etc., and which have a decisive influence on the performance of the luminaire itself. Therefore, for the purposes of a correct evaluation of the efficiency of a lamp, the values to be taken into account are those expressed in Lux which define the illuminance, that is the result of the relationship between the luminous flux emitted by the source (measured in Lumen), the aperture and shape of the light beam and the distance of the illuminated object. For this purpose, the manufacturers provide files (IES) that perfectly reproduce the spatial distribution of the light beam and that can be used in lighting design.

 The color temperature (CCT)

 Color temperature indicates the appearance of the color emitted by a light source compared to a reference value and measured in Kelvin (k). In the case of lighting fixtures, the radiation emitted in the range between 2650k and 8000k, ranging from so-called warm white to cold white, is taken into consideration.

This index has a high importance in evaluating correct lighting according to the activities carried out, as the color temperature of the light has an important effect on the human being.

The warmer color temperatures (2700k / 3200k) are indicated in domestic and recreational environments, while in places where work activities are carried out, higher color temperatures (3500k / 4500k) are preferred, which guarantee optimal visibility and promote concentration. The white LEDs used in illuminotencina have a range of color temperatures that covers the whole range from 2650k to 6000k and the ability to accurately select the color temperature of the LEDs allows you to use the same product in different areas based on the specifications. need. .

 The color rendering index (CRI)

 Color rendering is the ability of a light source to render colors in the same way as solar radiation. The Color Rendering Index is a measure of the balance of the chromatic components of white light and is determined by comparing the radiation emitted by the light source in question with the emission spectrum of the Sun. The reference values are: - Ra excellent = 90> 100 - Ra good = 70> 90 - Ra moderate = 50> 70

LED lamps have a color rendering that varies according to the type and quality of the LED chip used, currently the best chips produced by companies such as CREE, NICHIA, SHARP, SAMSUNG, etc. guarantee Ra values higher than 90.

 The direct glare index (UGR)

 The European Standard EN 12464 in relation to the use of artificial light in indoor environments refers to the average "maintained" illuminance value, to the limitation of direct glare generated by the lighting bodies and to the color rendering of the lamps, with distinction between the task -area where the visual task takes place and the surrounding areas.

The UGR (Unified Glare Rating) direct glare index takes into account the direct glare produced by luminaires within the visual field and the luminance of the background with respect to the observer. The evaluation of this index is essential when designing lighting systems for work environments,

  The flicker of light (Flicker)

 In alternating current electrical systems the power supply frequency is 50Hz (cycles per second), i.e. the voltage varies from + 230V to -230V, 50 times per second and reaches zero twice in a cycle (sinusoid). The fluorescent and low consumption lamps that operate in these systems produce light with a flicker frequency of 100Hz, in simpler terms the power is turned on and off 100 times per second.

Humans cannot perceive this flicker at frequencies above 50Hz, but the light receptors in some more sensitive people can sense it and this can cause discomfort and discomfort. It can also cause an annoying flicker in the images shot by a video camera, if you do not take the necessary precautions.

Theoretically LED luminaires using a power supply or direct current should guarantee but in reality many products, especially the very cheap ones, use low quality power supplies.

Only quality products can guarantee the use of flicker-free power supplies in which this type of phenomena are completely absent.

The simplest way to check is to frame the light emitted with a camera.