An Engineer in Wonderland – LEDs and lenses – a reality check

Electronics Weekly sometimes requests device samples.

It is not that the team doesn’t believe the specifications we are sent every day, it is just that it can be tricky to put 77dBA or 33 lm into perspective.

18feb09cree3shrunk.jpgThe latest items to arrive in the post are a Cree MC-E power LED development board and some matching Eva collimators from Finnish lens maker Ledil.

The specifications are on the respective web sites, but what are the devices actually like?

18feb09cree2shrunk.jpgWell, at an unknown power input, the LED produces a huge amount of light and it is dazzling to look at even from several metres away.
As for total light output, I would say one bare MC-E per room could be used at ceiling level as a stand-by for power cuts. This would be more than enough to safely move around by.

The Eva optics produce nice even beams. Moving the lenses with respect to the LED almost never projects a trace of the dark cross between the four die.

Unless they are involved with mountain rescue, I cannot imagine anyone needing a torch that puts out more light than an LED of this output combined with a suitable lens.

18feb09cree1shrunk.jpgThe MC-E/Eva (medium) combination easily lights a garden enough to look for the dog, for example.

A couple of us had a go at working out a distance where accidentally shining the light at someone might dazzle them, but at least they wouldn’t wince – and came up with 55m – so please add some dimmer settings if you are thinking about making a torch.

There would be a bit more about the narrow version of Eva, if I had not lost it in a pub while showing a caving friend what the combination could do – sorry Ledil. 

He was so impressed that he wants me to make him a caving head lamp, but I am not sure I can handle the responsibility of building a life-critical device.

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  1. I have fixed the link on the blog so the Eva data sheet is now available.
    By co-incidence, a while ago I asked Carclo if a lens optimised for cycle use was likely, but I fear that it does not fit the business model of collimator makers.
    I agree about head torch use – although I find daytime orienteering difficult enough without trying it in the dark.
    I have owned quite a few led head torches.
    Apart from greater battery life, the benefit of leds for me is that they can be dimmed – the same light can be used for long-distance viewing as well as reading in bed.
    The latest, bought for running, is an LED Lenser H7R, which has both variable intensity and a variable beam width.
    Having used it, this last feature is not perfect, but is good – much better than the old Petzl Zoom variable width beam.

  2. ooohhhh…… Cree MC-E! Definitely in the “I don’t need it, but I want it” category! Also in the queue for my next bike headlight design!
    What were the specs for the Ledil lens?? Any chance of sweet talking the Ledil rep into providing something appropriate for bike headlights (a beam width of about 10 degrees or so)? I’d be interested in seeing how it works out.
    The nice thing about the MC-E is that while it can be run at 12 watts, it can also be run at 1 watt or less. Very versatile.
    Steve K.

  3. “Unless they are involved with mountain rescue, I cannot imagine anyone needing a torch that puts out more light than an LED of this output combined with a suitable lens.”
    Sounds useful for Night Orienteering actually, provided you don’t have to run around with a heavy battery pack.

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