Is Headlight Glare Making Night Driving Harder?

I'm not a lighting engineer, but I suspect the problem is the 'luminous emittance', the amount of light emitted per unit area, for LED head lights results in a much more concentrated light source, which when you look at that incredibly concentrated source of light then results in momentary blinding.

Typical higher powered LEDs, have a flat construction with light emitted from a small area, on one side only, directly forward and not dispersed, so all of that light is coming from a small area, so is incredibly bright and intense. 

Compared to a traditional head light, where the light from the bulb is emitted in all directions, so spread over a much bigger surface area with the reflector then reflecting and spreading that light forward through a much larger glass or plastic lense, the surface area of the reflector is many times greater than the surface of the LED, so the light is less concentrated and intense than the LED, so less of a blinding effect.

It's like if you look at a clear filament light bulb, the intense light from the filament is uncomfortable and somewhat blinding, a pearl light bulb with a coating on the bulb spreads the light more evenly across the surface of the bulb so it's less blinding and uncomfortable, and if you put that bulb in an opal glass lamp shade, which spreads the light over something the size of a football, it's not uncomfortable or blinding at all. 

It's likely the design of the head-lamp, the LED needs fitting with a diffuser to spread the light more evenly and reduce the peak intensity. 

Long ago France required selective yellow headlamps as they were supposed to reduce the glare compared to normal white bulbs by removing the blue component.

https://en.wikipedia.org/wiki/Selective_yellow

To me the newer headlamps seem a very blue white rather than the more yellow conventional tungsten filament lamps. Maybe appropriate design of the LED wavelength spectrum or filtering would bring a reduction in glare.

I do agree that the very sharply defined beam of the new designs are good on a good road but can be very distracting on rough roads. Maybe the soft beam edges reduced this problem with conventional headlamps.

I remember having to paint our UK car headlight lense with the yellow tint for the drive to Italy.  As I recall France and Switzerland had the requirement for when were drove Mont-Blanc tunnels and Great St Bernard Pass.  My understanding was that this was on the premise of Fog or possible fog.  With the yellow working better than white in the same sense as dipped lights as apposed to Full beam in Fog.  I also recall the UK car needed a kind of black triangular sticker placed on the outside light lense to deflect/cover a certain portion as to not blind the oncoming traffic on the continent

Roger B said:

I do agree that the very sharply defined beam of the new designs are good on a good road but can be very distracting on rough roads. Maybe the soft beam edges reduced this problem with conventional headlamps.

It's not just the intensity of the beam as a whole, I think it is highly likely that within that beam there is part of it which is coming directly from the front-facing surface of the LED which has massively higher intensity, which then causes the momentary blindness.

I had a quick look at the LED head-lights on my car (original factory installed I should add!), looking through the lense to see the LED light source, you can actually see the front face of the LED, the familiar yellow coloured phosphor applied to the LED chips, so looking into the beam you would see not only the general beam ss a whole including light redirected forward from the reflector, but also a central, blindingly bright, peak intensity light, coming directly from the LED chip(s) which would inevitably cause some degree of blind-spots or momentary blindness.

Roger B said:

I do agree that the very sharply defined beam of the new designs are good on a good road but can be very distracting on rough roads. Maybe the soft beam edges reduced this problem with conventional headlamps.

It's not just the intensity of the beam as a whole, I think it is highly likely that within that beam there is part of it which is coming directly from the front-facing surface of the LED which has massively higher intensity, which then causes the momentary blindness.

I had a quick look at the LED head-lights on my car (original factory installed I should add!), looking through the lense to see the LED light source, you can actually see the front face of the LED, the familiar yellow coloured phosphor applied to the LED chips, so looking into the beam you would see not only the general beam ss a whole including light redirected forward from the reflector, but also a central, blindingly bright, peak intensity light, coming directly from the LED chip(s) which would inevitably cause some degree of blind-spots or momentary blindness.