Your super powerful rear lights

[rogerzilla]

I suggest checking directly in line and at a few degrees offline vertically and horizontally.

Directly in line, and slightly off is useful, but I'd suggest 45° and 90° would also be informative.  The first value giving an idea of how fast the beam is falling off, and the second an indication of whether there is any attempt to make things visible from the side.  Some lights, like the CatEye TL-LD1100, deliberately have side facing LEDs, and it's a useful feature to my mind.

Within thinking/braking distance for a driver, the angle is more or less head-on anyway.  The off-axis illumination is important for two reasons: the light might not be perfectly aligned by the person fitting it, and HGV drivers sit significantly higher up than a car driver.  I would say that 10 degrees would be quite sufficient.

[TimO]

In an ideal world, I'd want a continuous plot from 0° to 90°.  In practice without a automated system for doing this, it would take impractically long to undertake.

I wasn't so much trying to get an idea of how well it was visible from rear approaching traffic, but how wide the overall spread was (and significant off angle spread would be useful at junctions, on curved roads).  Like front lights, some rear lights have very bright but very narrow beams, whereas others spread the light over a wide beam.

It would be easier to measure some characteristics of the width by going significantly off bore.  If you just go a little bit off bore, the light level may be 90% or 88% down, the difference between which would be fiddly to measure.  If you went significantly off bore, say 30° or 45°, the drop would be more significant, as would be the differences, so noise in the measurement would be less important.

[rogerzilla]

Rear lights are interesting because it all comes down to perception rather than light output.  We can't measure the effect of different flash rates objectively, for instance.  And is a small intense point more noticeable than a large block of red light?  Car rear lights tend toward the latter, bike lights (for reasons of packaging) towards the former, although the unique Fibre Flare has more in common with the car type (in practice I believe the FF's visibility in flashing mode results from a WTF? factor, because there is nothing else that size and shape which turns on and off so rapidly).

We might also need comparisons for a busy street with traffic and an unlit road.  Size might be more or less important than intensity when there are a lot of other light sources, including oncoming headlights and street lighting.

[Kim]

Okay, dusting off my latent social scientist, how about collecting some standardised photographs/videos of assorted lights at various angles, then getting a selection of victims undergrads subjects participants to bubble-sort^[1] them in order of subjective brightness/visibility/attention-gettingness/annoyingness to be stuck behind/coolness.  Then you just cook analyse the data using whichever poorly-understood statistical methodology gives the best headlines results that you like the best.  Childish giggling about "Spearman's wank" etc. optional.

It's not proper cold hard SCIENCE, but it would allow you to do a meaningful comparison of lights in terms of hard-to-quantify parameters like "side visibility at junctions" and "ability to stand out in traffic".



[1] Why yes, I did switch from Social Psychology to Computer Science after a year, how did you guess?

[Kim]

...I just suggested a bike light version of hotornot.com, didn't I?

[DrMekon]

Okay, dusting off my latent social scientist, how about collecting some standardised photographs/videos of assorted lights at various angles, then getting a selection of victims undergrads subjects participants to bubble-sort^[1] them in order of subjective brightness/visibility/attention-gettingness/annoyingness to be stuck behind/coolness.  Then you just cook analyse the data using whichever poorly-understood statistical methodology gives the best headlines results that you like the best.  Childish giggling about "Spearman's wank" etc. optional.

It's not proper cold hard SCIENCE, but it would allow you to do a meaningful comparison of lights in terms of hard-to-quantify parameters like "side visibility at junctions" and "ability to stand out in traffic".



[1] Why yes, I did switch from Social Psychology to Computer Science after a year, how did you guess?

It's not science at all without a null hypothesis*.

That aside, if you set up a standardised scene that approximates road conditions (say in a carpark, next to a car and a ped in bright clothes), just replacing the light for each photo, I could run the Itti and Koch visual salience algorithm on them in Matlab, and rank them in terms of number of modelled eye saccades. That would smell** a bit more sciencey, at least.

*Experimental social psych can be as cold, hard and sciencey as you like. Guess who didn't switch from social psychology (and likes Popper more than Feyerabend when it comes to epistemology of science).

**My better half coined the phrase "smells of science" after getting lost in the chemistry dept when trying to find me in a psychlab block at the arse end of campus - I think it beautifully captures the conflation of the work associated with scientific enterprise in the natural sciences with scientific method.

[Wendy]

What car do you have Roger?

[rogerzilla]

A 1997 MX-5.  The rating of the lamps* is governed by various ECE regulations, though, and should be the same for any car.

Taillamps are 5W
Main brake lamps, reversing lamps, indicators and foglight are all 21W

*except the third brake light, if fitted, which varies between 16W and 21W for a filament lamp, and is often LED anyway.

[Ray 6701]

I used my raleigh astrum tonight & ended up changing it for my cateye ld1100.  I used the astrum under my carradice with the cateye attached to it.  I just thought the astrum was too bright, unless you can angle it slightly down I think they are a little too bright/dazzling  

[Wendy]

Having sat behind a BMW last night in my car and seeing the intensity of his lights, I feel nothing whatsoever about using a dinotte.  I've yet to have a driver complain about my taillight being too bright, which slightly dismays me, but shows that it's not all that bright or all that annoying.

[LittleWheelsandBig]

So when are we doing the rear light test? I can bring (looks at random assortment of lights within reach) a Radbot 1000, Smart Superflash, Blackburn Mars 4.0, Spanninga SBA, Vistalight 300 (5 LED), Cateye LD600, Cateye AU100 and a Brompton/Spanninga battery taillight.

[TimO]

I can do a CatEye LD1100, RSP Astrum, Dinotte 140R, Light & Motion Vis 180, and an Exposure Flare (with RCR123A rechargeable battery) if it ever arrives from the supplier.

(If also got some of the ones LittleWheelsandBig mentioned, but there doesn't seem any point in bringing those).

[TimO]

...and an Exposure Flare (with RCR123A rechargeable battery) if it ever arrives from the supplier.

This will not turn up for at least two weeks, although I've been promised it before...

[Wendy]

This will not turn up for at least two weeks, although I've been promised it before...

I had a look at one of those recently.  The single LED is nearly as bright as one Dinotte 400L LED, and doesn't have quite as wide a throw.

[TimO]

I'm actually getting it as an emergency spare for group rides, since it should be fittable on most people's bikes, without any special tools or problems (assuming somewhere on the seat tube is accessible, which I'll admit isn't always the case).

If it has a lower setting than full blast, this is more likely to be useful.

[LittleWheelsandBig]

That gives us a couple of weeks to sort out a test procedure, location and date. I was thinking that casting the beam onto the inside of a cylinder segment (quarter circumference) would show beam width and intensity distribution. Along with Rogerzilla's suggestion of standing beside a car's taillights in a carpark would cover most bases.

[Charlotte]

The SEEKRIT BUNKER is at our disposal...

[Wendy]

I could probably come along with my 400L.

[TimO]

That gives us a couple of weeks to sort out a test procedure, location and date. I was thinking that casting the beam onto the inside of a cylinder segment (quarter circumference) would show beam width and intensity distribution. Along with Rogerzilla's suggestion of standing beside a car's taillights in a carpark would cover most bases.

Good ideas, but I think an actual numeric measurement of light intensity at it's peak along the boresite, even if uncalibrated, just as a comparative value, would also be very useful.

Unfortunately I don't have any sort of light meter, or know where we can get a cheap one.

[Charlotte]

Oh arse:

Light And Motion Vis 180 Tail light

[Riggers]

I'd be saying 'arse' too at £90 for a rear light.

[mattc]

I'm actually getting it as an emergency spare for group rides, since it should be fittable on most people's bikes, without any special tools or problems (assuming somewhere on the seat tube is accessible, which I'll admit isn't always the case).

If I were a good samaritan choosing that sort of light, I'd pick something with a very wide, non-directional illumination. That way, if you have to bodge some hideous attachment to their bag/rack/saddle/whatever it will still make them pretty safe.

[seat-post is useless with most rack-packs, likewise seat-stays if panniers are fitted]

[Somnolent]

I do wish there was more choice in AA powered rear lights.

I have AAs in my Hope front light, my Garmin Legend HCx, my Petzl head torch.... but all the small & lightweight rear lights are AAA, and it just seems a PITA to have to carry two sizes of spare battery.

I do have a Cateye LD-1100, but it seems awfully big & heavy for something which takes 2 AAs.

[mattc]

I do wish there was more choice in AA powered rear lights.

I have AAs in my Hope front light, my Garmin Legend HCx, my Petzl head torch.... but all the small & lightweight rear lights are AAA, and it just seems a PITA to have to carry two sizes of spare battery.

I do have a Cateye LD-1100, but it seems awfully big & heavy for something which takes 2 AAs.

I know what you mean, but i've stopped worrying about it. Because:
- Rears last (almost) forever. On any short ride, if they're OK when you set off, you'll be OK. On longer rides, carry spares or put fresh batts in.
- AAAs are much lighter. This is good. But also means that a spare light with 2xAAAs in it is no heavier than 2xAA batteries*. Plus you have a spare light - lights can fail even with full batts in them.



*I haven't checked this fact. But I'm pretty sure 2 x AAA-equipped lights weighs less than AA-equipped light +  2 spare batteries.

[TimO]

Oh arse:

Light And Motion Vis 180 Tail light

Oh come on, keep up, I already mentioned it back on Page 4.  

It's not a bad light, it's rather compact and light, and has a couple of nice "Throbbing" modes, like the Radbot.

It has a few downsides;  The sliding approach to getting it on and off the clamp can make it difficult to fit somewhere useful, you essentially need twice it's length to be clear somewhere on your bike.  The chunky rubber band arrangement seems to work OK, but why do they think someone fitting a £80 light can't use a screwdriver, which would give a much more solid and reliable mounting.  The battery life isn't brilliant.  On continuous it's about 4 hours (according to the spec) and up to 8 hours in flashing (but there are two flashing modes, one dimmer than the other, and which of them lasts 8 hours isn't clear).  Not really enough for many night rides, at least not by itself.

Oh, and the "documentation" is pants, it's a handful of poorly designed ideograms on the packaging.