The truth behind Hi-Viz

As we all know, High Visibility clothing is seen as a must have safety item for cyclists. With the biggest selling items being jackets and rucksack covers.

High visibility clothing or fabric is made up of a fabric which is bright in colour and often has fluorescent properties, in addition there are reflective strips. The fluorescent properties of the material only work in natural light and the reflective strips only work if a light source is shining on it.

Fluorescent clothing works best during hours of natural light because the clothing ‘converts’ ultra-violet light into visible wavelengths, which makes it appear brighter than other colours and objects. It’s noted that it stands out considerably during poor conditions, such as rain and fog. Light from non-natural sources doesn’t contain much ultra-violet and thus the fluorescent properties of the clothing provide no advantage against non fluorescent clothes.

In most cases, the reflective panels on hi-viz clothing are designed to reflect light back at the source, in a handful of cases the reflective panels reflect light in all directions, this usually weakens the appearance of the reflected light. The more common type of reflective material (known as retro-reflective), reflects light at only a few degrees. So the performance of a reflector can appear very different from the perspective of a lorry driver vs a car driver. As the observation angle increases, the performance of the reflector drops.

So hi-viz is made up of two parts, one being good for day time visibility and one being good for night-time visibility. But they have their drawbacks. With growing numbers for road users being seen wearing fluorescent clothing it can have the effect of making you blend in with others and thus not standing out from the crowd, not the effect you always want. The retro-reflective material only reflects light back at the observer if they shine light at it.

The limits to retro-reflective material can be seen quiet clearly in the pictures below. Due to car headlights shining no higher than the waist of the average person. Any retro-reflective material won’t shine back a strong light because there isn’t much shining on it. In one of the pictures I lower the hi-viz cover into the headlights of the car and quiet clearly there is a difference between the two.

High visibility clothing is obviously great for standing out. After all that is what it is designed for. Cyclists in a busy city have to weigh up the options. At night the Hi-viz jackets and rucksack covers are next to useless unless you have rolling hills. During the day they can help you stand out but if you get into a group of other cyclists you may blend in, which can result in someone miss-reading your speed.

During the day I think it is personal choice about wearing hi-viz jackets, I personally don’t, I would much rather turn my lights on than wear yellow.
During hours of darkness I don’t see the point in wearing hi-viz jackets, it adds limited visibility. You would be much better off wearing retro-reflective on the legs and feet. Not only are these in the headlight zone of a motorised vehicle but they also move as you pedal. Adding in a much more attention grabbing effect.