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

Sometimes a picture (or a wiggly line) tells a thousand words

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.