LEZ wrote:

Lost for Words - Thanks for the heads up on this subject, what you say makes perfect sense (to me anyway) and can save us the unnecessary cost of replacements.

 Visiting from DISCO3.CO.UK
Discovery 3 TDV6 Auto HSE Zambezi Silver

dantastic wrote:

@Lost for Words, I'm not arguing your figures. But if we perceive a certain light as brighter, is it not brighter then?
Vision is a sense the same way as hearing is. There are frequencies the human ear can't hear and you can obviously measure "sound" some instrument makes and say one instrument is louder than another. But if I can hear one but the other is mostly outside the frequencies I can hear then the exercise is purely academic.

What I'm saying is, humans can't be 'measured' the same way. And if I perceive one light to be brighter than another then why isn't it? Are you saying that I can't see more detail in the "picture" in front of me even though I perceive the light to be brighter?

And if I can't - do I perhaps find it easier to see - even though I mightn't see 'more'?

I do understand; the logic does not present itself in a straight forward manner! There are two factors - 1) the receiptiveness of the human eye to different wavelengths and 2) the mental effect of colour temperature.

The key point I'm making regarding Night Breakers acually entails primarily the latter. In short, the ingrained mentality is that a "whiter" light is brighter, because we can very easily judge colour temperature. Thanks to our eyes adapting so well to differing light conditions, we cannot tell accurately how bright something is without a much larger difference in luminous intensity. The upshot of it is that humans will look at two equally bright sources of light and think that the "whiter" one is brighter even when what you can actually see is the same.

To help visualise, here's a random "HID vs halogen" comparison picture I took from the internet.


Click image to enlarge

Most people would look at that and instinctively say the bottom one is brighter. This is the same picture desaturated:


Click image to enlarge

Now you can see how little there actually is in it (The HID probably is brighter but the camera settings have ironed it out - the human eye does this to an extent also).

There is not only this effect, but also a change in the perception of colour temperature according to light conditions; for example, a 4300K HID bulb will appear white at night, but a bit yellow in daylight. This is because our eyes use not only our pupils, but also rods in our eyes to couteract for changing light levels, and rods are most receptive to blue light. It's called the Kruithof Curve.

Following on from the above, the first factor is another matter also. The human eye uses rods and cones to see light and these are more sensitive at different wavelengths. Mostly, it's cones that are responsible for our daytime colour vision, while rods start to come into play more at night causing our colour vision to degrade somewhat.



Light towards the yellow and red end of the spectrum is best absorbed by cones, and so a warmer light temperature encourages photopic vision and the pupil to constrict allowing better focus. Bluer light is found to be more glaring (another thing that makes people perceive it as brighter) for this reason and it forms the same basis of selective yellow headlights/fog lights. There are also psycological and hormonal effects of a higher colour temperature light that can increase fatigue during lower luminance levels. Manufacturers often use statements like "close to daylight" to suggest that it gives better vision; sounds very logical, but that is not the case.

The example of sound is a very good one, because certain wavelengths and forms of sound are also perceived very differently, and so weightings have been developed to accurately describe sound in human ear terms.

So what I'm saying here, is that we should not treat such "whiter" or "bluer" light with such high regard, because it's not beneficial to human vision. The final note I would add is that more light is not always better - it's the balance of light that allows one to see. Like a set of scales, if you put equal weight on both sides it will be balanced no matter how much weight that is.

I hope this helps clarify a few things.  Visiting from DISCO3.CO.UK
Discovery 3 TDV6 Auto HSE Zambezi Silver

Quote:

The lumen (symbol: lm) is the SI derived unit of luminous flux, a measure of the total quantity of visible light emitted by a source. Luminous flux differs from power (radiant flux) in that radiant flux includes all electromagnetic waves emitted, while luminous flux is weighted according to a model of the human eye's sensitivity to various wavelengths.

So however you weight your bulb's output the lumen figure will take that in to account.

What gives? Something's not right somewhere.



Edit: from Osram:


The only thing I can think is that if there's more going on to the road there's less going in the air. But that's not down to the bulb is it?