The 7 graphs that tell you everything you need to know about lighting

1    How LED overtook all the other technologies in efficacy

The light source efficacy race begins with incandescent, which is pretty much the only contender until low-pressure sodium shows up – more efficient, but orange. Then mercury and fluorescent arrive on the scene with better colour quality, followed by high-pressure sodium. Halogen appears some time around 1990, matching incandescent’s colour quality, with greater efficiency and longer life. But they were all outpaced in the space of a few decades by the light source of today: LED. 

  • Thanks to Mike Simpson at Philips for the graph


2    How heat slowly kills LEDs

An 11°C difference in junction temperature makes a 35,000 hour difference in life (measured to L50 – in other words, when the light output has declined to 50 per cent of what it was at the beginning).

  • Thanks to Brian Charman at Philips for the graph


3    How different light sources create white light

To the human eye, one white light looks very much like another. But different light sources can be composed of very different combinations of colours, which has a big impact on how they render colours, and how the light affects our bodies. 


Different light sources can be composed of very different combinations of colours, which has a big impact on how they render colours"











4    Why controls are like Space Invaders

Remember in Space Invaders how you used to hide behind the little shields, and the invaders would gradually shoot through them? Well these graphs of how controls can hack away at your energy use in an office are kind of the same. Only with electricity bills instead of shields and err… aliens instead of dimming?

The first one, in green, shows your energy use with no controls (except switching the lights on when the first person gets in and off when the last person leaves). The red graph shows what happens with the introduction of some time control to save energy when the office is quieter. The purple graph introduces some occupancy control, so that energy use drops dramatically when people are out of the office on breaks or at lunch. And the last graph shows what happens when you introduce daylight control, taking a big satisfying chunk out of your energy use right in the middle of the day.





5    The long-term cost of T5 and LED

LED might have a bigger upfront cost than traditional solutions such as T5 fluorescent, but think about the cost over time. Simon Waldron of Sainsbury’s came up with this graph of the cumulative cost of T5 vs LED.

  • Thanks to Simon Waldron at Sainsbury’s for the graph


6    Google searches for fluorescent and LEDs

If you want to know what the people of the world are interested in about right now, Google’s Trends feature is very useful. This graph shows the number of Google searches for ‘fluorescent’ and the number for ‘led lights’, over the last decade. Any questions?


7    How much energy the world could save on lighting

According to the International Energy Agency,  the world consumed 19 trillion kWh of electricity in 2014. Lighting represents about 19 per cent of that, or 3.6 trillion kWh. With low-energy lighting and controls, we reckon you could easily cut that in half, saving 1.8 trillion kWh a year. That’s 18 times the amount of electricity produced by the world’s largest power plant, China’s Three Gorges Dam.


Comments 3

" Any questions?" Well, yeah, what are the units on the graphs? Otherwise they are useless. And why the bump in the LED costs between 10 and 11 (years? Parsecs? Furlongs??)

Our firm is involved in research and the practical application of light for environments that support the health and well-being of living beings. Since 2002, when the iPRG cells in the eye were discovered and their role in health and wellness first explored, there has been an explosion of research into spectral effects of light on all living beings, from microbes and plants to fish and humans. For example, there is considerable, widely accepted evidence of the negative effects of short wavelength light exposure on circadian systems. More recently, there is a report on short wavelength visible and UV on damage to the eye ( Lougheed, Tim, March 2014. "Hidden Blue Hazard? LED Lighting and Retinal Damage in Rats". Environmental Health Perspectives 122). The problem is, the process of properly collecting and evaluating the research findings and undertaking to develop codes and principles of good practice is a long term effort by the CIE, which a month ago announced that our ability to provide benefits to the general population at this time is impossible without more research and more collective evaluation by CIE members and special panels of scientists from around the world. The International Dark Sky Association was the first organization to warn of blue-rich light in outdoor lighting in 2009, and its recommendations were fully supported by the American Medical Association in 2012. Yet despite this, cities around the world seem hell-bent on installing high CCT LED street lighting for the "energy savings". I feel this is not rational and there is probably a healthy compromise, but precious little funding to find it. We've been engaged in a successful 2700K LED street lighting program in Davis, California (Lighting Design and Application, June 2015) that has convinced one thoughtful city government to listen. We are working on programs in other communities, but the battle against the efficiency-at-any-cost people is hard given their comparatively deep pockets and entrenched (but faulty) science.

The wavelength graph is an eye opener. Does anyone have a study on any effects on human eye.

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