Big vs many small

jdp298

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Bit of a conundrum. I have a pair of 1W LEDs at the front of my bike, they work just fine. At the back I have half a Watt of 8mm SUNLED standard looking LEDs in a Lucas motorbike rear lamp housing. Originally I had gone with a single 0.5W red LED star. It wasn't nearly as bright or as diffuse as the array of 11 8mm LEDs in there now.

So the question comes. Would it be better to get one Watt of small LEDs (15 by my reckoning) or to stay with the single big one? Are smaller LEDs more efficient still?

Essential comparisons I can't square away are the mcd vs Lumen problem. The maths is no problem and easy to understand, once you can think in solid angles. It's not helping me understand which would be better though.

8mm LED: 17990 mcd, viewing angle 15 deg
1W LED: 90 Lumen, viewing angle 120 deg

I also have a 10 deg lens over each big LED which helps focus but doesn't stop the flood as they're inside Union-style bullet-shaped dynamo reflectors which are quite wide.

Hopefully that's enoug to get us going.
 

Matt King

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Brightness is only one factor, and probably the least important (once you reach the level of "visible").

Viewing angle is very important, something where the 15° LEDs will suck, unless you fan them across a large width (but then horizontally they need to be well aimed) or as you say diffuse them through a lens.

I also feel that a single emitter will not give you good "presence", ie it is hard for observers to judge the distance to a sharp spot. Emitting light from a larger surface area makes you look like a more solid object, and makes size/distance judgement much easier. See a typical German taillight for example.
 

fyrstormer

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Multiple plastic-encased LEDs can work if they're aimed in multiple directions. Otherwise, a single unfocused surface-mount LED will be visible from a wider angle. However, as the previous poster pointed out, a single point of light will not give the viewer a good sense of distance.
 

jdp298

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Matt

Spot on with the angular resolution. If the eye only sees 1 'pixel' (for want of a better term) of bright light, it is harder to place it, no question.

I suppose what I really wanted to know is the efficiency of a small one vs a big one.
 
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