Fibre flare optical efficiency vs reverse red led on surface

[SA_SA_SA]

I wonder what the optical efficiency (light from Led against useful light exiting the fibre but ignoring the fact that some is lost against the background (eg saddlebag)) and how it compares to that of a (shielded*)red led shining onto a large white or red material (eg fabric). You could get a bigger lit area from that.

I have a suspicion that size of illuminated red area might make a lower brightness lamp more effective (ie a old fashioned 4cd Durabeam lockable vs a 20cd Never ready NightRider rear: the Durabeam somehow seemed a rather unexpectedly effective large glow from a distance even though less intense).

Yes I suppose like a front lightrider, but for the rear: the idea seems much more suited to less intense rear "lamps" than the front.

*to comply with the "no red light to show to the front of a vehicle" law.

[[XAP]Bob]

So have a red light on a stick shining at a ~retroreflective surface on the rear of the pannier/saddlebag...

Could work quite well...

[gaz]

ie a old fashioned 4cd Durabeam lockable ... the Durabeam somehow seemed a rather unexpectedly effective large glow from a distance even though less intense).

Do you mean one of these?

DSCN0685.JPG

[SA_SA_SA]

..... old fashioned 4cd Durabeam lockable ...
Do you mean one of these?

Yes. What was the 1st generation?

[redfacedbaldfatman]

So have a red light on a stick shining at a ~retroreflective surface on the rear of the pannier/saddlebag...

Could work quite well...

Retro reflective reflects mostly directly back to the light source, so it won't spread it around like you hope it would.

[gaz]

To the untrained eye the second generation are indistinguishable from the first.

The standard mounting bracket (spade) is slightly different although I suspect it would still fit both versions. The second generation rear lamp had an additional bracket to allow it to be mounted horizontally when attached to a seat stay, extremely ugly looking thing. I can't recall any other differences in the optics, appearance or mechanics. Both complied to BS6102/3.

I've honestly no idea of the candela figures for either this lamp or the Nightrider but back in the day it received some positive anecdotal comments. Phillips PR2 bulb, 2.38v 0.5a currently fitted which I suspect is the original but I can't confirm.

Edit: Lens measures 85x60mm approx.

[[XAP]Bob]

So have a red light on a stick shining at a ~retroreflective surface on the rear of the pannier/saddlebag...

Could work quite well...

Retro reflective reflects mostly directly back to the light source, so it won't spread it around like you hope it would.

Hence my use of the tilde to signify "roughly"

[SA_SA_SA]

So have a red light on a stick shining at a ~retroreflective surface on the rear of the pannier/saddlebag...

I wasn't sure if the retro ref would be too retro -reflective and reflect most light back at the small led rather giving a wide angle illumination: perhaps glass bead material would be best due to its working from wider angles of observation. I think I remember CJ commenting on the lightrider that a white screen would reflect only 50% of the incident light.

[SA_SA_SA]

Actually, it was a Never Ready technical person who quoted the approx 4cd figure for the Durabeam to me, (whilst mentioning the NightRider's 20cd)
I wonder if that was with a 0.75W (0,3A) 7lumen bulb, which was then increased to 1W (0.5amp) 11lumens in order for the Durabeam to pass BS6102/3 rather the old BS3648.

[gaz]

Sounds a little suspect to me. 4cd is the minimum required by BS6102/3 for the intensity of the beam centre of a rear lamp.

Reflectalite suggest the Nightrider had a slightly lower wattage bulb. As I recall the Nightrider had just a plain reflector and the lens. That lens must have had some quite incredible optics to raise the intensity of the beam centre to 20cd (or did the Duracell have some incredible optics to reduce the intensity of the beam centre to 4cd ) .

It's amazing what you can achieve with different mouldings of some red translucent plastic .

[alexnharvey]

I would like a larger area, less point focused rear light. Is that what this thread is about? Philips saferide limiting is one piton but I wish it were even larger and more diffuse.

[SA_SA_SA]

...As I recall the Nightrider had just a plain reflector and the lens. That lens must have had some quite incredible optics to raise the intensity of the beam centre to 20cd (or did the Duracell have some incredible optics to reduce the intensity of the beam centre to 4cd ) .

No both duracell and nightrrider red lens had prisms in them. Also the parabola collects and concentrates the light then the lens modifies it further. The Nightrider was brighter than the Durabeam because it concentrated the light into a narrow letterbox: so was much dimmer even slightly off the central axis. The successor Never Ready rear night vision lamp was somewhere between the two IMO, a better compromise IMO.

The standard Nightrider bulb was 2.7V 0.42A (1.1W)

[Brucey]

With the never-readies, I thought the 0.42A bulb was for the front and that the rear had a lower wattage one in it (the idea being that if you put in fresh batteries all round, it would always be the front that conked out first, thus never leaving you with a rear light out, assuming it stayed on, that is... ). I could be wrong though.

I think you need to ask yourself what you are trying to achieve here; 'being noticed' is so much more than mere lumens, and you have to ask yourself 'by what'? If it is 'noticed by something with headlights', a diffuse light soon becomes no brighter than a decent retro-reflector would be.

Note also that although lumens are not everything, as soon as you use them in reverse mode (ie. onto a viewed surface) you are probably throwing most of them away anyway; between losses and scattering a simple white surface isn't that efficient.

BTW I don't think you can use a retroreflective as the illuminated/viewed surface; the light will simply go straight back to the emitter. For an appreciable amount to miss the emitter and escape, the emitter would have to subtend less than ~0.5 deg solid angle to the reflector. I think this is just not on, not in a single unit on a bike.

cheers

[SA_SA_SA]

I would like a larger area, less point focused rear light. Is that what this thread is about? Philips saferide limiting is one piton but I wish it were even larger and more diffuse.

Sort of:
more of an idea for a homemade alternative to the fibre flare which hopefully keeps the fibbre flare's rearward omnidirectionality with a possibly large(r) evenly lit area.

[SA_SA_SA]

With the never-readies, I thought the 0.42A bulb was for the front and that the rear had a lower wattage one in it ...

No the rear (mine anyway) came with the 2.7V 0.42A bulb and ever ready said (to me) that was because the then new silver seal ZnCl cells would shorten the bulb life of a 2.5V 0.3A bulb compared to zinc carbon.