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Choosing LEDs

Efficiency

Manufacturer’s claims vary wildly about the efficiency of LEDs and can often be quite misleading. The simplest way to ensure that you are comparing “like with like” is to look at the efficiency in Lumens per Watt. That is, how much light do you get for each Watt of electricity used. Today (early 2010), LEDs that are in production range in efficiency from about 20 to 60 Lumens per Watt. New developments should increase this to around 80 or 100 Lumens per Watt over the next few years. This compares with around 10-15 Lumens per Watt for old-fashioned incandescent lamps and 50-100 Lumens per Watt for fluorescent tubes.

Colour rendering

The colour rendering of LEDs varies quite markedly between brands. For some applications this is not particularly important but for ambient lighting it is important to check the quality of light emitted. The LEDs that we offer for ambient lighting all have good colour rendering, comparable to that of a good quality fluorescent tube. Many manufacturers do not however quote a colour rendering index for their LEDs so we are rarely able to quote specific figures.

Heat output

LEDs give off relatively little heat but do run reasonably warm and often incorporate a heat sink to dissipate any excess heat and maintain the LEDs at optimum operating temperature. Compact lamps such as miniature spot lights can thus still get reasonably warm whereas larger bulbs and candles certainly cool enough to touch when operating.

Rated Life

The one area where LEDs really score highly is in their rated operating life which typically ranges from 20,000 to 50,000 hours. This is 20 to 50 times longer than a typical incandescent lamp so LEDs are ideal for use in areas where maintenance is difficult or long life is important.

Colour Temperature

Early LEDs were mostly a very much higher colour temperature (ie a bluish light) than the typical 2700K colour temperature of a warm white incandescent lamp. This has led many people to think that LEDs gave a “cold” light. LED technology has however advanced a great deal in the last couple of years and some types of LED are available in a range of colour temperatures from warm white (2700 or 3000K) up to daylight (6000K and beyond). LEDs with a higher colour temperature do however tend to be slightly more efficient than those with a lower colour temperature so some companies offer these as a way of making their products seem brighter. To replace standard incandescent or halogen lamps, a colour temperature of around 2700K to 3300K is preferred. Some companies use non-standard terms when describing the colour of LEDs such as “natural white” or “office white” which cannot be readily compared with other products. To ensure that you are comparing like with like always check the colour temperature. 

With traditional incandescent or halogen bulbs you couldn't choose the colour of the light the bulb produced as this was down to pure physics. Traditional bulbs work by passing electricity through a wire that glows hot. This glow produces the light that can be seen. Because LED bulbs are a completely different technology and much more technically advanced it is possible to choose the colour of the light that you want.

Without getting too technical, the colour temperature of light can be measured as a number on the Kelvin scale. This is represented by a number followed by the symbol “K”. 

High colour temperatures of over 5000K are said to be cool colours and often have a blue tone to them.

Whereas low colour temperatures of 2,500 – 3,200 are said to be warm colours and have yellow or orangey tones to them.

A few examples of the difference in Kelvin are as follows:

  • A candle flame has a Kelvin value of 1,850K
  • Traditional Incandescent lights have a Kelvin value of between 2,700K – 3,300K
  • Moonlight has a Kelvin value of 4,100K
  • On an overcast day, the light would be around 6,500K

 

With LED bulbs there are usually two options of white colour available and they are normally referred to as warm white or cool white. warm white is usually around 3000K and cool white around 5000-6000K. When choosing your bulbs you should check the Kelvin value of the bulb.

In domestic lighting, 75 – 80% of customers buy warm white LED bulbs as they offer the closest match to their old incandescent or halogen bulbs that they are replacing. The light given off by a warm white LED bulb can be described as soft and warm with a slight yellow hint to it.

Some customers purchase cool white LED bulbs if they want the brightest light possible or if they want to achieve a modern look to a room. This particularly suits colour schemes that are bright and bold and use primary colours, or even colour schemes that are predominantly white where a clean minimal look is required.

It’s also possible to use both warm and cool white bulbs in the same room on different switches to give the user different options on how they want the room to look. For example in a kitchen you may want warm white bulbs in the ceiling for everyday use but also have under unit lighting in cool white in order to give a very different effect at night once the main lights are off.

In commercial lighting the majority of customers opt for cool white bulbs. These give a brighter light but you should be careful to ensure that the colour temperature is not too high, or in practical terms the light not too cool, otherwise the effect may seem very harsh or displeasing to the eye.

 

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