Self Illumination?

[snailracer]

Retro-reflectives only work when the light source and viewer are at co-located. Which is why cars driving with foglights on & headlights off is one of my pet hates. I also hate buses and lorries - their headlights can be 5 feet or more below the driver's eye level - totally crap and unsafe design.

 

[BentMikey]

Retro-reflectives only work when the light source and viewer are at co-located. Which is why cars driving with foglights on & headlights off is one of my pet hates. I also hate buses and lorries - their headlights can be 5 feet or more below the driver's eye level - totally crap and unsafe design.

Well yes, that's much what I said further up the topic, but a couple of people don't seem to understand that retro-reflectives only return light parallel to the inbound path, with any return falling off very quickly within a few degrees off-axis.

 

[Jezston]

Sorry I thought what you meant earlier was that reflectives only work when headlights are pointed DIRECTLY at them, which is what I was refuting. Obviously pointed directly away from them won't catch any light either.

Having said all that, the light in the picture in your first post seems WAY too bright. It's much brighter than the headlights of the car next to it suggesting it would dazzle anyone coming towards you.

 

[Jezston]

I'm not sure I follow.

 

[snailracer]

That isn't true, Mikey - light from car headlights whilst focused onto a fixed spot on the road is actually scattered albeit weakly over quite a wide area, and as you said you only need a little light for reflectives to catch it and jump out - which is why big road signs on the side of a motorway are easily and quite well illuminated with their reflective elements despite being above and to the left of the direction headlights face.

Headlights are specifically designed to throw extra light above and to the left of the main spot. If they didn't, drivers really would miss more signs. If you drive a UK-spec car in Europe, you are expected to fit "beam-benders" that throw light above and to the right of the main spot.

But the main point you still seem to be missing is that the car headlights and driver's eyes are fairly closely located - the illuminating and reflected rays are still roughly parallel (or, more correctly, anti-parallel) whether the reflective target is off to the side or straight on. Streetlights, other headlights (unless they're from cars directly behind yours) don't produce a strong reflection from reflectives.

 

[snailracer]

[QUOTE 1242110"]
The point of contention on this thread is that reflectives are pointless when you're on a main road and a driver is looking to pull out of a side road, on the basis that the angle of return is slim. That's reliant on the only light source on the road being the headlights of the driver in the side road. That's rarely the case, and there are often light sources present that will return a beam back to the driver.
[/quote]
Yes, but unless those beams are closely anti-parallel to a line drawn between the driver's eye and the reflective target, the target will appear no brighter than a flat white target.
In which case, a bright top would be more visible, because the total area of reflectives is usually pretty skimpy on most hiviz tops.

 

[snailracer]

[QUOTE 1242112"]
How close are you talking? As I've already said, the 3M reflectors on the spokes of my kids' bikes reflect light from lapposts back to me when I'm out walking with them. That's a greater angle than a car travelling in the opposite direction to the bike in the side road scenario.

The fact is that reflectives aren't pointless. There are some scenarios where they won't be effective of course, but there are plenty of others which makes wearing them worthwhile.
[/quote]
Reflectives that have wider acceptance angles are however less-visible than their narrow-angle equivalents when illuminated from narrow angles - the choice of acceptance angle is a compromise. A simple white top can be thought of as a reflective with a 180 degree acceptance angle.

The law specifies that a rear reflector (which is essentially a narrow-angle reflective) must be fitted to bikes because the illuminated-by-overtaking-cars-from-behind is a common scenario where the acceptance angle is narrow and the reflector therefore appears very bright. The law does not require a front reflector, because it's much less effective - there are fewer scenarios where a front reflector is brightly illuminated with a narrow acceptance angle.

UPDATE: In some of the jurisdictions I have lived (USA), the minimum legal lighting requirement for cycling at night are a rear reflector combined with a front light. In other words, the authorities there also didn't think reflectives were adequately visible from the front, although they were considered adequate for the rear.

PS I don't consider reflectives pointless, I think they're great, especially on the back of a jacket.

 

[BentMikey]

As snailracer says, there might be a lot of light sources around, but they are almost never in line with the driver's eyes and the cyclist, so you won't see the reflectives. See the image below with cars passing on the main road and behind the camera (although you'll have to take my word for that), street lights everywhere, etc. There is no return from the hiviz vest.

There were at least two cars behind the camera, driving towards us, when I took this photo. There's still no retro-reflective return, for obvious reasons once you understand how retro-reflectives work.

When you have decent lights, the hiviz becomes pointless. Useless in fact.

 

[PpPete]

When you have decent lights, the hiviz becomes pointless. Useless in fact.

My experience, as a motorist, of coming up on cyclists from behind is that their retroreflectives often stand out brighter than their their pathetic little blinkies.
The trousers with two horizontal bands on each leg are especially effective IME.... right in line with headlights and moving up and down.

OTH I nearly took out a ninja last night....no lights, no bike reflectors, no h-viz.....i was lucky he was wearing dark clothing....it made him blacker than the surroundings so I saw him just in time.

 

[gaz]

[QUOTE 1242116"]


When you understand how light works, you'll realise that this view is also incorrect. Unless your lights have a 360 degree beam around you.
[/quote]
I have two fibre flares, one on each seat stay pointing away from the bike. This means I have a light that is always visible at what ever angle you look at the bike.

 

[ComedyPilot]

In my very recent experience, having 2 very bright flashing LEDs on the front and a reflective dayglo jacket will not stop a silver Volvo V70 overtaking and coming straight at you. I even moved out to primary to make sure my lights moved 'across' their line of sight instead of staying in one place and being seemingly 'stationary'.

I am getting more militant in my opinion of drivers. They CAN see us, they just decide that THEY will drive at us anyway, and it's up to us to get out of their way.

 

[PpPete]

In my very recent experience, having 2 very bright flashing LEDs on the front and a reflective dayglo jacket will not stop a silver Volvo V70 overtaking and coming straight at you. I even moved out to primary to make sure my lights moved 'across' there line of sight instead of staying in one place and being seemingly 'stationary'.

I am getting more militant in my opinion of drivers. They CAN see us, they just decide that THEY will drive at us anyway, and it's up to us to get out of their way.

probably says more about Volvo drivers than the way light reflects..... I'm safe, f*ck the rest of you.

 

[snailracer]

I looked up the viewing angle of 3M Scotchlite material: it is 0.2 degrees, which seems remarkably narrow to me

European specs seem to measure performance at viewing angles of around 1.5 degree and narrower.

 

[gaz]

[QUOTE 1242122"]

[/quote]

I like the look of these spoke reflectors, tempted to buy some tape.

 

[BSRU]

I like the look of these spoke reflectors, tempted to buy some tape.

I think they are Sekuclips designed for bicycle spokes.