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LED Lighting - Terminology

Every new technology comes with it's own technical jargon. Detailed on this page you will find answers to some of the more common questions associated with our LED lighting products. Need some advice? Contact us now.

 

Colour Rendering Index (CRI)

CRI is a numerical representation of how accurately a light source portrays colour with a scale running from 0 to 100. A light source with a poor CRI e.g. low pressure sodium (as found in yellow streetlights) will make all colours look very similar whereas a light source with a high CRI will make greens look green, yellows look yellow and blues look blue etc. It is advisable to use CRI >80 for commercial/domestic usage and CRI>70 for industrial usage - some special applications use CRI>90 or higher. It is worth noting that the CRI number is an average taken across the colour spectrum, some "high CRI" sources have very poor response in the red part of the light spectrum but are good elsewhere. If accurate colour rendering is important to your project, it is worth checking the values across the whole spectrum.

Correlated Colour Temperature (CCT)

This is the measurement of how "warm" or "cold" a light source is and is measured in Kelvin. Warmer, more yellow colour temperatures are lower down the scale (typically 3000K or lower) and colder, bluer colour temperatures are higher (typically 5500K or higher). Generally speaking, lower colour temperatures are less efficient but have better CRI whereas higher colour temperatures have higher efficacy and lower CRI.

Corrosion Resistance

Primarily of concern in marine/coastal environments or where abrasive chemicals are commonly used, corrosion protection usually takes the form of specifying products made from materials which do not react to the usage environment or by some form of protective coating. Although often a little more expensive than standard products, those which have been designed to cope with corrosive environments will usually prove their worth quickly against non-corrosion resistant equivalents.

Driver

Other than the LED chips, the other major component of an LED light fitting is the driver (sometimes referred to as a PSU, control gear or ballast). This converts and smooths the incoming electricity supply (usually 230V AC across the EU) to fit the much lower voltage requirements of the LEDs. This component is where most failures occur in LED fittings - lifetime is generally governed by the quality of the sub-components (particularly capacitors) and temperature.

Efficacy (Lumens Per Watt)

Efficacy is a measure of how much light a light source produces for the energy put in to it. This is normally expressed in lm/W (lumens per watt). With LED sources, efficacy is advancing at a rate of roughly double every 3 years although (as with lumen degradation) this varies with drive current and temperature. Like most markets, there is a wide variety of quality and cost - efficacy is one of the most important parameters in selecting an LED light fitting. High end products can reach around 150 lm/W or even higher whereas typically the budget end of the market can be as low as 70 or 80 lm/W, meaning that they are around half the efficiency of their premium counterparts!

Flicker-Free Illumination

Glare is an extremely important consideration in many lighting applications - particularly from a health and safety standpoint in the workplace, for sports lighting and to also to ensure that an artificially lit environment is visually comfortable. Glare is essentially how bright the light source appears compared to the surrounding area whilst looking in its direction - the UGR is a numerical way to represent the glare characteristics from a variety of angles. A high UGR is the reason why some light sources appear to be extremely bright to look at but do not actually provide much light at ground level.

IK Rating (Impact)

This is a measurement of how well a product can withstand a physical impact. Rated on a scale of 0-10 (sometimes higher numbers are quoted but the official scale stops at 10!) they are typically only of importance in areas where it is reasonable to expect occasional impact e.g. in a sports hall or where vandalism may be a concern.

IP Rating (Ingress)

The IP rating of a product is a 2 digit measure (from 00 to 68) of how well it is sealed against solid objects and moisture. The first number is rated on a scale of 0-6 (or X which means it has not been tested) and the second is rated on a scale of 0-8 (or X which means it has not been tested). Typically these are unimportant for many indoor applications however anything which is installed outside or in a heavy duty industrial application should be at minimum IP54, preferably at least IP65.

L70

See "Lumen Degradation"

LED Lighting - Light Emitting Diodes

These are the electrical components which produce the light within an LED fitting or luminaire and give this type of lighting its name. Also known as Light Engines or chips, in many ways they are similar to a solar panel working in reverse, using semiconductor diodes to convert electricity into light. While they have long been used as low power indicator lights, it is only relatively recently that the technology has advanced enough to become a serious force in the lighting market. As with any market, there is a wide variety of product prices and qualities - when choosing between products, two of the most important factors are lumen degradation and efficacy.

Lumen Degradation

All light sources lose brightness over time, whether LED, fluorescent, incandescent etc. - this is known as lumen degradation. The lumen degradation of LED lights is primarily dependent on chip quality, the current flowing through the chips (known as drive current - lower is generally better) and temperature. One of the primary differences between high and low quality LED fittings is thermal design - high quality LED luminaires are designed to radiate heat effectively to keep components cool and slow lumen degradation. An LED luminaire's lifetime is commonly modelled as its L70 point -i.e. the point at which lumen output has reduced to 70% of its initial value. Most good quality LED fittings should have an L70 value of at least 50,000 hours.

Lumens

Lumens are the unit of measurement for the amount of light a light source emits (known as luminance). This is the most common metric when comparing lighting products or estimating the suitability of a light for a particular application, however, with the correct application of precision optics this is not necessarily a fair way to compare products. It is important that you ensure it is luminaire (or fitting) output rather than chip output you are checking when comparing products to ensure that it is representative of the product - depending on lenses/diffusers etc, there can be a fairly significant step down from chip output to luminaire output.

Luminaire Output Ratio (LOR)

As mentioned above, the amount of light emitted by the luminaire is usually lower than that emitted by the chips themselves. The light output ratio is (as it sounds!) the ratio of luminaire output compared to chip output. Typically any type of diffuser/reflector will reduce the LOR compared to a simple glass/polycarbonate cover. LOR is generally much higher for LED products than comparable traditional systems, meaning that although some claim that T5 systems are almost as efficient as LED systems - because they emit light in 360 they typically require reflector systems to direct the light, resulting in much lower LOR.

Lux

Lux is the unit of measurement for illuminance. The difference between lumens and lux can often cause confusion. It can be most easily explained by thinking of luminance as the amount of light emitted from a light source whereas illuminance is the amount of light at a particular point away from the light source. 1 lux means 1 lumen per square metre.

Maintenance Factor (MF)

As well as lumen depreciation, dust/dirt accumulation on light fittings and room surfaces will affect light levels in the intervals between cleaning. To account for these (and other variables) a "maintenance factor" is used in lighting designs. This is a number ranging from 0-1 (typically 0.8 is used for LED products by default)and it is multiplied by the results of the design calculations with the aim of simulating lux levels at a particular point in product lifetime/cleaning cycles. This is almost always taken to be the mid-point unless stated otherwise. It is important to consider that if you are comparing designs with the same maintenance factor and one product has a much longer lifetime than the other, the light levels from the longer lifespan product will remain higher than the simulated maintenance factor for longer.

Traditional Fittings

Traditional Fittings is a term used to describe the light fittings which pre-dated LED luminaires. These are typically Halogen, Sodium, Metal Halide or Fluorescent based products and are in most cases inefficent in terms of output and maintenance costs.

Unified Glare Rating (UGR)

Glare is an extremely important consideration in many lighting applications - particularly from a health and safety standpoint in the workplace, for sports lighting and to also to ensure that an artificially lit environment is visually comfortable. Glare is essentially how bright the light source appears compared to the surrounding area whilst looking in its direction - the UGR is a numerical way to represent the glare characteristics from a variety of angles. A high UGR is the reason why some light sources appear to be extremely bright to look at but do not actually provide much light at ground level.

Uniformity

As the name suggests, this is a measure of how "uniform" or even the light levels are in an area - i.e. the variation between darker and lighter areas. Usually abbreviated to U0 in lighting designs, it is measured on a scale of 0-1, with higher values being better. Careful consideration of boundary zones (the perimeter area excluded from the calculations) must be taken to ensure the area being analysed is representative of the usage.

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