A little about lighting

An overview of important concepts.


Lux is a term used to
explain amount of light. It describes it
the light that falls on a surface and tells
thus how illuminated a surface is.
e.g. a work table. Because it
describes the amount of light falling
on a surface, the amount of light will vary in
in relation to how far the light source is from the surface it is to illuminate. Lux as a measuring parameter is a lot
well suited for measuring the amount of light as it is relatively easy to measure with a lux meter.

Lumen (lm)

Lumen is the amount of light that flows out of a light source in all directions. That is, how much light a light source emits or the efficiency of the light source. In contrast to LUX, Lumen is difficult to measure, ie the measurement must be done in a laboratory. That is, the lumen cannot be measured in the field. Lumen pr. Watt (lm / W) tells how efficient the light source is, or in other words the efficiency of the light source.

CRI and RA

Ra index (Rendering Average) is a scale that was created for conventional light sources, and should describe the light source's ability to reproduce colors correctly. The scale goes from 0 - 100% and is an average measurement of a given scale that consists of 8 calibrated pastel colors. CRI (Color Rendering Index) is a description used on LED light sources and reproduces colors on a scale from 0-100%. Color reproduction for LEDs is not quite the same as with traditional light sources, because LED is a full spectrum light source. Ie. that LED has all the colors in the visible part of the light spectrum, which conventional light sources do not have. The lighting industry is working on creating a new CRI method that is better suited for LED. So far, several colors have been implemented in the existing scale so that it is now up to 14 colors. There are also saturated colors. This scale is used today but cannot be used to indicate Ra or CRI. At most manufacturers of LEDs, a CRI is stated based on the old method, but in addition the values ​​of each of the 14 measuring points are stated. This gives a sense of how good the LED light source is with a view to reproducing colors correctly.

Worth thinking about!

It is always the case that when you choose high CRI you will get less light out of the light source ie less Lumen. This means that there is a contradiction between CRI and Lumen.
Since LED is a full spectrum light source, the CRI 80 on an LED will be better than the CRI 90 on a conventional light source.

K (Kelvin)

This is the color temperature of the light and is measured on a scale from hot to cold. The higher up you get on the scale, the colder the light feels. It is important to note that we are talking about a feeling. In Norway we prefer relatively warm light, about 2700K - 3000K. In Southern Europe, a slightly colder light, about 4000K, is often preferred.

Worth thinking about.

How cold or hot the light is in K will affect the light output Lm. So you get more light from a light source that has a higher Kelvin. As with CRI, K (Kelvin) will affect the efficiency of the light source. This means that with LED it is difficult to get both in a bag and a sack. L / W 50000t. Example L80 / B20 50000t then says that you have 80% of the light left (20% light decline) and 20% of the LEDs no longer light after they have been lit for 50 hours.

Life expectancy calculation
With the introduction of LED, it became important to create a standard that would say something about longevity and quality. An Internatsional standard has therefore been created for this. In Europe, the IEC (International Electrotechnical Commission) is responsible for this in regulations IEC 62717 LED modules for general lighting - performance requirements. IEC states that as a threshold value applies @ 25 ° C L70 B50 50 hours. This means that all LEDs that satisfy this requirement are of good quality.

What do the individual values ​​mean?

@ 25 ° C: Means that the other values ​​apply at an ambient temperature of a maximum of 25 ° C

L: tells you the percentage of light that is left after a given time compared to what the light source had when it was new. There are 3 different levels: L90, L80 and L70. L90 says that it should be 90% of the original light level back when you reach the expected life.

B: Says that it is probable that not all LEDs satisfy the requirement for remaining light after the stated service life. However, the population of LEDs must still satisfy the requirement for remaining light. Two values ​​are used here B10 or B50. For lighting designers, this means that this value is not taken into account when calculating light in a lifetime cycle.

Worth thinking about.

IEC's threshold value @ 25 ° C L70 B50 50 hours is set to this level because the human eye does not perceive a light decline of less than 30%. This means that it is difficult to say that the L90 is significantly better than the L70 in practice. On paper yes, but in reality it will be very difficult to distinguish these qualities from each other.

In the case of so-called high-efficiency LEDs, these will have great difficulty in reaching a level above L70 at 50 hours.

The reason is that the service life of LEDs is strongly linked to heat generation and thus added power. An LED operated at 800mA or 30W or higher will hardly be able to meet the requirements of L90 50 hours. When talking about service life, it is also important to remember that the driver in the luminaire is involved in determining the service life and it is rare for a driver to have a service life of more than 000 hours.

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