HOW TO...

LEDs expert Gordon Routledge gives his 10 golden rules for specifying LED luminaires

Colour

Colour temperatures with LEDs can vary from 2800 all the way up to 10,000K or Alien Autopsy white as it’s known in the trade. If you’re trying to replace halogen go for around 3000K – don’t be tempted to use 5000K just because the efficiency is better.

Colour rendering

Make sure the colour rendering matches your application – warmer white LEDs tend to have higher colour rendering, and many now offer over Ra 90 – but with higher degrees of colour rendering you have a severe drop off in terms of overall efficiency.

Watts

Many manufacturers have developed the annoying habit of specifying the wattage over more common lighting terms – A 3W LED must be better than a 1 watt unit, which isn’t necessarily true.  The cost and quality of LED chips vary by manufacturer – it’s easy to dump power in to them without seeing improved light output.

Lumens

LED modules are difficult to measure in the same way as light bulbs and this leads to a number of errors. The worst case is when LED chip data is translated into light output from a real fitting – not accounting for optical and thermal loss of the whole luminaire. Make sure the quoted lumens is what is leaving the fixture.

Candelas

Often manufacturers use candela light output values instead of lumens, particularly in spotlight applications. While the candela value may equal that of a conventional halogen lamp – the lumen output doesn’t. This is okay in true spot lighting applications, such as retail display – but if you’re relying on those stray lumens to light a room – you may be in for an underwhelming experience.

White

It may surprise you that white LEDs – regardless of colour temperature or colour rendering – can actually offer more shades than a paint catalogue. Often refered to as binning – tight binning usually results in less product to product variation – but it also costs the manufacturer more to source these LEDs.

Efficiency

Make sure you understand the lumens per circuit watt as this incorporates all the system losses, including optical, thermal and electrical losses Lots of headline figures give impressive LED chip efficiencies – but these soon evaporate with a low grade optical system, inefficient driver and poor thermal management.

Heat

Efficient thermal management is key to the long term reliability and performance of LED devices. Will the superefficient heatsink still work when the back of the unit is covered in insulation? If the sample is red hot on the desk, it’s only going to get worse in the ceiling.

Drivers

If chosen correctly, the power supply should last as long as the LED module. But cheap often means  low power factor, higher power losses and flickering on the LEDs.

Design

Get the manufacturer to prove the design. Ask for an accurate lighting design layout, and compare this with other older technologies to make sure the numbers stack up.

 

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