Clarity in the solid state age

The watt is not a very useful measure of a light source – particularly when there are so many available

The UK went metric in 1971, three years before I was born. Many would not believe this, because of my rapidly greying hair, which I attribute to 15 years of working in this industry and a few too many heated debates with electrical contractors.

As a result, I was educated in a metric world. Weights and length were taught in grams and metres, not pounds, feet and inches. But, like many others, I would struggle to remember my height in metres and my weight in kilos; and if someone else tries to quote a metric equivalent, my mind always converts this back to the imperial equivalent to establish a point of reference.

I know that it’s exactly two miles from my house to my local pub, and as a reward for my journey I can enjoy a few pints of beer. If I walked in the door of said establishment complaining about my 3.22- kilometre journey, and dire need for 568ml of their finest ale, I’d get a pretty strange reaction, in fact I’d probably be thrown out for such impertinence.

Six of one

To be fair, I’m quite happy to buy fruit, vegetables and meat in metric, because our European pals dictated some time ago that displaying pounds and ounces is illegal. Also, when I need six apples, I know I need six apples. I don’t care if they are 500g or 1lb.

Probably half the population will have been educated under the metric system, so when will we finally leave behind the learned behaviour? Probably when we are forced kicking and screaming to remove miles from our road signs and dashboards.

What on earth does all this have to do with lighting? Well the universal unit of lighting equivalence is watts, as in the unit of energy consumption. Just as carrots are sold by the kilo,and beer by the pint, light is sold by the watt. Look through any manufacturer’s catalogue and the prevalent unit is the watt – 50W halogen downlight, 2x 32W CFL downlight, 10W LED downlight. What on earth am I buying? Why do we do this?

It is of course learned behaviour. If we go back to the humble incandescent lamp, 100W is about 1,000 lumens, and 60W is 600 lumens. Simple, and the purchase of the lamp was a separate activity to the purchase of the fixture. If you weren’t happy with the light levels, then change the lamp, a relatively cost- effective exercise.

Now we live in a complex world of high-efficiency lamps, optics and a myriad of different lighting techniques and fixtures, but our point of reference for all this complexity is still the watt. Skilled practitioners can visualise what 100W of LED light will deliver versus 100W of CFL light1 Actually they can’t – the truth is buried in diagrams, spacing tables and down loadable photometric files, if we believe them.

We need to stop the confusion, especially in the brave new LED world, where the lamp source and lighting fixture are sold as an integrated unit, welded together for life. I’ve seen 100W LED fixtures that are very efficient and cool running and 100W inefficient LED fixtures that blister your skin when touched. Lamps, washing machines and fridge-freezers have to be labelled at the point of sale with the key energy information and display a rating from A to G. Even an M&S sandwich has key performance staring you in the face – opt for roast beef with lard and you’re risking a coronary on the A1.

A few manufacturers get it. Pick up their data sheets and you’ll see the real lumen output, the real input power, and in a few cases the energy saving compared with the product it is most likely to replace. This is clear information, which makes it easier for end users, and mere mortals not blessed with a LIF certificate and a copy of Relux to make a reasonably informed choice.

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