Correlated Colour Temperature (CCT) and Colour Rendering Index (CRI)

There are two parameters which define the colour of LED light. – colour temperature and colour rendering.

Colour temperature is the perceived colour of the light source.  It is compared with a glowing black body source.  When heated to around 3000K it will glow a warm yellow (think about a 40 watt filament lamp).  When heated to 4000K you get whiter (neutral white) and when heated to 5-7000K you get a bluey white (daylight or cool white).

Warm white is most useful in domestic environments and tends to provide a “homely” feel.  Neutral white is more suited to the office environment as it is slightly brighter than warm white and easier to see by.  Cool white provides the most light for a given amount of power but may appear harsher so but is ideal where good visibility is required such as a gym or car park.

Colour rendering is the ability of the light source to allow colours to be seen accurately and is not directly related to colour temperature.

White light is made from a mixture of colours.  A white LED has a blue source with a yellow phosphor overlay which emits white light when illuminated by the blue source.  Needless to say, the colour rendering may not be great.  Reds will appear purple and oranges rather muddy.  

This is because there is no red within the light source to reflect from the red surface.

In simple terms, the solution is the addition of red phosphors to the yellow overlay.  This provides the red to reflect from the red surface and give a good colour rendering.  It would be desirable if this could be added to all LED coatings but, as always, the issue is cost.  Red phosphors are significantly more expensive than yellow so the cost of the LED goes up.

Does it matter?  In many cases no, but it may have safety implications.

For example, old low pressure sodium (LPS) street lights have a colour rendering index of 20 – pretty poor.  They may be bright but a red car will appear black and may simply be invisible at night.

A moderate to good colour rendering of 70-80 is almost certainly adequate.  The fact that a royal blue shirt may appear simply as dark blue probably isn’t important.  It’s also reasonable for security cameras as it will provide good contrast.

A high colour rendering of 90 or more is probably only required if comparing absolute colours, perhaps in paint or fabric manufacture or in retail.  With a really high colour rendering oranges will look really orange and may sell better than your competitors and you can match a shirt and tie exactly so they will look the same in daylight. (although it is still wise to ask the lady in your life).

So, it’s a choice between budget and application.  You could pay 15-20% more for a high colour rendering so it’s worth asking the question…is it necessary?

At Earlsmann we use CREE LEDs for most of our products.  These are available from 2700K to 6500K and with a CRI up to 95 so we can accommodate most requirements

Cree Announces Next-Generation XP LED Delivering 200 Lumens Per Watt

If you missed the recent announcement from CREE about their latest product release then it's worth a read now

DURHAM, NC -- Cree, Inc. (Nasdaq: CREE) introduces the XLamp® XP-L LED, the first commercially available single-die LED to achieve breakthrough efficacy of up to 200 lumens per watt (LPW) at 350 mA. Delivering up to 1226 lumens in a 3.45 mm x 3.45 mm package, the game-changing Cree® XLamp XP-L LED enables an immediate performance increase of 50 percent or more as a drop-in upgrade for lighting designs based on Cree’s market-leading XLamp XP-G LEDs. 

Read the whole story here

With a world leading manufacturer like CREE it won't surprise anyone to learn that Earlsmann uses their LEDs, almost exclusively, in our products.   In fact, we actually use their COB (chip on board) 2530 which achieves a very creditable 112lm per system Watt (350mA) in our Lincoln Street light with gull wing lens - this takes account of power supply and lens losses.  For the bare COB, at 800mA, the CREE published figure is around 24lm/W.

It is worth mentioning that CREE characterise their products with a junction temperature of 85 deg.C  Many of their competitors quote their products at a junction temp. of 25 deg C which is quite unachievable unless the ambient temperature is around freezing!   What's more, some lighting manufacturers quote the LED life in their data - a bit misleading, I think, as it can't be achieved. 

More on LED specifying next time...
LM80/TM21 

Indoor Tennis Court Lighting

I’ve recently come across a rather novel way of lighting indoor courts which I think worth sharing as it is very effective and very cost effective.

I was asked to quote to replace the lighting on an indoor tennis court.  Simple enough, but the current arrangement was rather unusual.  It was lit with 4x6ft fluorescent fittings the entire length of the court on both sides located more or less at 6m directly above the doubles side lines. (off the playing area) They were angled at about 30deg from vertical.

One solution is obviously to simply replace the tubes with LED but this would mean rewiring each fitting and cleaning the diffusers.

I considered a different approach and modelled the court with our Turin 600x600 suspended ceiling panel and was amazed at the result.

Good overall illumination and uniformity, minimal glare and, since these panels are solid, unlike the fluorescent fittings, they are robust and less prone to damage from mis-hit balls.

 Of course it's not just indoor tennis you can light this way.  Bowling greens, squash, badminton - anything where glare would be an issue.

If you have something you need lit - give us the challenge to come up with something different

Daylight Harvesting with Earlsmann LED Lighting

Daylight harvesting is a technique that is becoming popular as a very good way to keep energy usage to a minimum.  Why pay to run your lighting when the sun can provide all the light you need?  How often do you go into an office and discover the lights are on and the sun is blazing outside.  In fact, you may not actually notice the lights are on the sun is so bright!

All you need to do is turn the lights off to make immediate savings but that (almost) never happens.

A good starting point is a motion sensor as they will turn the lights off for you when nobody is about but this has its own problems as it can quite often be much gloomier at desks farthest from the window.  The solution, of course, is daylight harvesting sensors to maintain a constant lux.  These continuously monitor the amount of light falling on the work surface and adjust the light output from the luminaire accordingly to keep it to the required level.  These can be incorporated in the luminaire so those sitting closest to the window where daylight could easily be 700 or 800 lux would have minimal artificial light whilst those sitting with, perhaps, only 100 lux from daylight can have it boosted to 300 lux or more, as desired, by the luminaire.

With modern controls and LED luminaires this is very easy to achieve.  The initial investment in controls is slightly higher than for fittings without but the payback time is similar and the ongoing savings far greater.

Constant Lux with Brighton LED Bay light

In the picture above we used our 120 Watt Brighton LED bay light to achieve around 700 lux

If you’d like to know more, or to discuss your own requirements, please get in touch.

The LED vs Heat

Heat is a real enemy to the LED whether it is a replacement GU10 or a full luminaire so it is a constant battle to achieve a good design to reduce heat whilst achieving a high lumen output.

How often do you see GU10s looking very sorry for themselves?  Looking blue? Looking a bit jaded?  And this can happen after just a few hundreds of hours.

There are a couple of reasons; first, the design/quality of the lamp is simply very poor and it has failed after a short period or second, the lamp has overheated causing premature failure.

It is less likely these days for the lamp to be of poor design as manufacturing techniques have improved and component prices have come down.  You will notice most GU10 lamps have some sort of heatsink – or fins – around the LED and the miniature power supply is built into the end.  In free air this is almost certainly adequate – ensure good circulation and the heat is taken away from the components.  However, the majority of these lamps get used in the popular downlighter which is very effective at preventing good air flow past the fins.  Not surprising, really, as they were designed for halogen lamps with temperatures up to 700deg C with no need for cooling.

These are usually installed in ceilings with next to no airflow, trapped between the ceiling and the floor above and hidden under layers of insulation.  These areas get hotter and hotter, particularly in summer, and can quickly exceed the safe ambient temperature required around the lamp, typically 35degC. Be aware that whilst the ambient air temperature you can measure may be 30deg C, (apparently “safe”) the important ambient around the lamp itself could easily be 30 or 40 degrees higher, well in excess of safe operating limits for the components.  It will be far worse when used in the fire hood often required to meet fire regs.

The solution? Don’t install replacement lamps in luminaires designed for traditional light sources as they can’t keep ventilate but if you do, make sure there is adequate air flow to keep them cool.

Ideally use a complete luminaire designed specifically for LEDs.  These will be designed with LED technology in mind and will achieve much higher efficacies than replacement lamps (>100lm/W compared with 50 or 60lm/W)

Replacement LED 2D lamps

Everyone, it seems, is offering an LED 2D lamp.  They’re great – plug straight into the existing luminaire socket – fit and forget!  They even come complete with sensor options and emergency packs.

But, have you ever stopped to think about the spec. and how they’re used? No? Well here are some things you may wish to consider.

Firstly fitting them – it’s not quite as straight forward as simply removing the CFL type and plug in the new LED version.  More than likely the luminaire will have a high frequency ballast which you need to disconnect and bypass.  Even with a magnetic one, to achieve maximum energy saving, you need to bypass the ballast.  In both cases rewiring of the fitting is needed.

Then there is the emergency pack.  Fluorescent packs do not work with LED lamps so you will need to buy the LED emergency pack and work out how to install it securely adding to the time, and therefore, the cost of replacement.

Then there is the spec.  Most LED replacement lamps are quoted at 12 watts and around 1000lm.  Indeed a huge saving over the fluorescent type but actually not quite enough light. The cool white ones are 1000 lumens but the chances are you’re replacing a warm/neutral white lamp.  You’re probably only getting 800 lumens from these – well short of what is required.

The Earlsmann solution is to replace the complete gear tray – simpler to install – just the Live, Neutral and Earth to connect and the extra permanent Live for the emergency version.  They are rated at 15 watts so use a bit more power but then they give you 1200 lumens which provides a light level far nearer the original fluorescent. They don’t cost any more than the replacement lamp solution and are quicker to fit.

Of course it may not be suitable for every luminaire so you’ll need to ask us.

Earlsmann at Ecobuild 2014 with the ILP

Ecobuild wasn’t an exhibition that had been on our list of priorities until we had a call from the Institution of Lighting Professionals (ILP) inviting us to join them in their “Lightscene” zone.

We agreed, and were really pleased with the result.  Simon did a 15 minute talk on the Wednesday, “ Lux, Lumens and Watts”, inspired by the ILP “Guide to the Specification of LED Lighting Products 2012” to help people make more informed choices about LED lighting.  After all, LED lighting is a significant investment so it’s important to avoid the many pitfalls. (Also read our other blog articles).

We also took the opportunity to show some of our new products and gauge reaction:-

The Lincoln LED streetlight is available from under £150 and will easily replace up to 90W SOX luminaires.  At the price, it may be a much better option for S class areas than simply replacing the lamp.  This was very well received and several requests for further information were made from as far afield as the UK, Belgium, Spain and Kenya.

The Brighton Bay / Dover flood lights have interchangeable reflectors making it possible to change the beam angle to suit specific applications and for change of use of areas within a building.  LED lighting is a major investment so “future proofing” was considered a good idea.

Replaceable LED geartrays for 2D CFL bulkheads are a good alternative to the readily available LED replacement lamp as the driver is separate and better cooled, allowing the light output to better match the traditional lamp.  The standard LED replacement lamp doesn’t quite have the light output to adequately replace CLFs.  What’s more, replacing the complete gear tray is quicker and easier to install than rewiring for the lamp.

We met with many professionals and lighting specifiers so hope to see an increase in business.  The coming months will tell.