LED has been a viable method of illumination for over ten years now and at John Cullen Lighting we offer a full range of LED lighting solutions, with our first LED luminaire sold in 2005. The challenge is to select the best LED solutions but this is not as straight forward as it might appear.
John Cullen Lighting’s Senior Product Designer, Matt Healey, gives us his tips to ensure you select the best quality LEDs for your projects.
Colour quality, referred as colour rendering, is what you need to start with when choosing the appropriate LED with Colour Rendering Index (CRI) being the current metric. CRI refers to the light source’s ability to accurately render colour compared to a pre-defined control source i.e. its fidelity. This method references 8 colours with each colour being given a rating between 1 and 100. The average of which is stated as a Ra value i.e. 80 Ra. Good quality LED products will have a CRI of over 90. The industry is moving towards a new method called TM-30-15 where the 8 reference colours to measure fidelity are replaced by 99 sample colours, the average of which is stated at Rf.
With LED it is important to consider colour consistency. This is because during the manufacture of an LED chip the colour can vary. An LED is essentially grown and although accuracy of this has improved over time consistency is still an issue. The colour consistency is an index relating to a light source’s range of variation in chromaticity (colour) that can be picked up by the human eye. Colour difference is defined by a steps of MacAdam ellipse. The scale is set by ANSI Chromaticity Standard. In short though the smaller the ellipse value (size) the smaller the colour difference.
A common misconception is that LEDs do not generate heat. Although the beam emitted is cool they do, like any other light source, convert power into heat. Lifetime of the LED Chip is directly linked to its operating temperature. Poor thermal management where the LED is operating above manufacture guidelines can also lead to colour shift. There are various methods of doing thermally manage this. At John Cullen we use the body of the luminaire to draw heat away from the LED chip. We do this by careful material selection and considered produce development. A competent manufacturer should fully test their luminaries and be able to offer their clients information such as maximum ambient temperature. Information such as this will ensure the client can be assured of lifetime and colour consistency of their investment in our lighting.
LED selection is getting easier as solution providers become more consistent with their product and data. Confidence comes with suppliers that can back up their claims with tested data and fair warranties.
Take a look at John Cullen’s full range of LED products at www.johncullenlighting.com/products