Finding the data to understand and compare lighting products can be nigh-on impossible sometimes. Here are seven things about datasheets that buyers find really annoying.
1. Can’t find the datasheet
Lighting companies’ websites can be fiendishly complicated. Often, there are hundreds of variations of thousands of products available, and the product line-up changes every few months.
The trend for busy, complicated sites with flashy visuals and mood music is all well and good if you’re a high-end designer who only makes bespoke lights for royals, but if you’re a typical commercial lighting manufacturer, keep it simple.
As we move into a post-catalogue age, where a company’s online presence is the first and perhaps only port of call for prospective buyers looking for information on what’s available. Make it clear, simple and searchable. With big, friendly buttons.
2. Can’t find the metric
So you’ve found the datasheet. Great! Now, where’s that colour-rendering index? Hmm… it doesn’t seem to be there. That’s strange, it seems like a pretty obvious number to include.
If you can’t find a key metric such as CRI, CCT, output, efficacy, life or wattage in a company’s datasheet, we think it’s fair to assume that the true figure just isn’t very good. If you can’t find the colour temperature, you can bet it’s higher than you’re expecting, and will make everything look a bit alien autopsy. After all, if the figure were respectable, why wouldn’t they just tell you? In some cases they’ll just have neglected to put it on for quite innocent reasons, of course. In which case they should pay more attention.
3. Fudging the numbers
You find the number you’re after, but instead of a simple figure, they give you some sort of range, like ‘>80’ or something including the dreadful phrase ‘up to’, which is really another way of saying ‘less than’.
This kind of number fudging is more common in promotional materials, but not unheard of on actual datasheets too. What you’ll also often see is figures lumped together for a whole range of products, giving only the specs of the best-performing product in each category. If a range of products (covering a number of wattages and colour temperatures, for instance) has an output of ’up to’ something, you’d better check the output of the particular version that you’ve ordered.
4. Metrics that can’t be compared
When you find the number you’re after, it’s incredibly frustrating when you can’t actually compare it to other manufacturers’ numbers because everyone cuts the numbers in a slightly different way. For instance, lifetime can be measured to the point when either 30 or 20 per cent of the light output has gone, or in a whole bunch of other ways. Sometimes it takes into account how often the light is switched on or off (which takes its toll), and sometimes it doesn’t. Colour-rendering figures, too, can refer to different selections of sample colours.
This is one problem that isn’t the manufacturers’ fault – this kind of thing can only really be solved at an industry level. And boy do buyers wish they would get on with it.
5. Wishful thinking
Lifetime claims are probably the single most annoying bit of product data. Manufacturers love to say their products last for 50 or 100,000 hours, on the basis that their friend told them that their brother-in-law told them that their chip supplier told them that the LED will last that long. It’s just not good enough – how long an LED lasts depends massively on the luminaire it’s built into, the electronics it’s used with, and whether it’s installed in Rio or Reykjavík.
And even if you get an honest lifetime metric, in almost every case this will have been extrapolated from test data taken over just 2,000-6,000 hours. The truth is, nobody really knows how long an LED product will last until it fails.
But for the best data, look for the figure for the luminaire as a unit, and for well-defined metrics such as L70, which tell you how long it will take for the output of the luminaire to fall to 70 per cent of what it was at the start.
6. Ignoring gear losses
Everyone knows drivers aren’t 100 per cent efficient. But some manufacturers will cheekily ignore the energy that’s wasted by a driver when they give you the efficacy numbers for their LED luminaire. The metric that you need to insist on here is luminaire lumens per circuit watt (we write it as lm/Wcct, you might see it formatted differently elsewhere).
This tells you not just how many lumens are emitted by the LED chip, but how many find their way out of the luminaire as a whole, and not just how many watts are used by the fitting, but how many are used in the entire circuit, including the driver. Asking, ‘how many luminaire lumens per circuit watt?’ is the same as asking, ‘how many lumens per watt – and let’s not play games?’
7. Outright lying
We all know it happens. And the sad thing about it is that the nice guys finish last. The manufacturers who tell you honestly how their products perform, who underestimate rather than overestimate the lifetime, who are clear with all the caveats and qualifications that make their data truly meaningful (Osram is famous for this, and we salute them for it), will also inevitably end up being the ones whose figures are less impressive. Because they’re actually true.