leeds wrote:

I wonder what the definition of a spot light is?

10 degrees seems to be the norm for a spot light, 30 degrees for a flood light. 5 degrees would be becoming a 'pencil beam'
A lot of LED light bars are combination bars i.e a mixture of flood and spot elements.

TBH, I've always lumped spot and pencil together as the same thing, being 10 degrees max, but preferably 5-ish. 20 for driving or 30 for a wider version, 40 to 50 for a normal main beam, and 60+ for flood, fog 90+ and flat. Of course, the distribution of light within the beam is just as important, so the basic angle is just rough descriptor. Having crewed for a rally team sponsored by PIAA many moons ago, I've always had the basis on their 5/20/95 for spot/drive/fog lamps (which is probably why I'm so picky about aux lighting).

Quote:

One thing is fairly certain no one light will suit every driver and all conditions.

Can a light be too bright? In my opinion in certain cases yes as you can get reflected back too much light. Reflected light from road signs is an obvious example, however if the light output is high then objects which would not appear reflective under a normal light seems to reflect back some light. Also when you go from a very bright LED light bar to 'normal' headlights you are 'blinded' for a few seconds as your eyes adapt to a big change in brightness. The older you get the longer it appears to take for your eyes to adapt.

You take a similar, more objective, view to me on such matters. So many people don't think about what lights they stick on their vehicle, and what they hope to achieve by it. I try to explain to people that Lux and Candela are the basis of vision, and not Lumens (so, for instance, one flood beam and one driving beam will do less to extend vision than just the driving beam alone). The colour spectrum and temperature is also worth considering - LED and HID lights are far inferior in this regard. As you say, the adaptations of our eyes have a huge effect (photopic, mesopic and scotopic vision, rods vs cones, and refraction within the eye). Sadly, a bright glaring beam makes people think it's better.  Visiting from DISCO3.CO.UK
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leeds wrote:

Can a light be too bright? In my opinion in certain cases yes as you can get reflected back too much light. Reflected light from road signs is an obvious example......Brendan

Very valid points from Brendan and L4W about type of lamps fitted. I purchased my Light Force 240XGTs as I used to travel from RAF Lyneham to Bournemouth twice a week late at night or in the very early hours of the morning. The light beam and spread across Salisbury Plain was ideal for my purposes at that time and wildlife could be spotted a great distance away from eye reflection, especially the blue from deer. I no longer do that commute, Defender usage has dropped and now my driving is less rural and more urban. The scenario explained by Brendan above is now the situation I can quite often find myself in. It has improved since changing the lenses from spot to combination.

Spot lenses.


Click image to enlarge

Combination with the opaque centres.


Click image to enlarge If you go through life with your head in the sand....all people will see is an ar5e!!

Treat every day as if it is your last....one day you will be right!!

Lost for Words wrote:

You take a similar, more objective, view to me on such matters. So many people don't think about what lights they stick on their vehicle, and what they hope to achieve by it. I try to explain to people that Lux and Candela are the basis of vision, and not Lumens (so, for instance, one flood beam and one driving beam will do less to extend vision than just the driving beam alone). The colour spectrum and temperature is also worth considering - LED and HID lights are far inferior in this regard. As you say, the adaptations of our eyes have a huge effect (photopic, mesopic and scotopic vision, rods vs cones, and refraction within the eye). Sadly, a bright glaring beam makes people think it's better.

leeds wrote:

Why do people refer to lights by the term watts? That has nothing to do with light output and watts is a unit of electrical power!

Lumens is the correct unit for total light output from a device whereas lux is light'density' and 1 lux is 1 lumen per square metre. What does 1lux mean in practical terms? It is basically the minimum light you would need to read a newspaper.

I guess such common use of Watts hails back to the days when everything was incandescent, and of similar efficiency.
People love to say "I have 20,000 lumens" etc., but it's entirely meaningless without a location, and intensity too. The sun produces 6,840,000,000,000,000,000,000,000,001 lumens (think that's the right figure) - is anyone any the wiser?

leeds wrote:

LfW, I am not sure I understand/agree with your comment that LED are inferior in respect of colour spectrum and temperature. Inferior in comparison to what? The yellow light output from old guttering Land Rover candles? I would agree that some of the poorer quality cheaper LED are very blue prone.

They're inferior by comparison with halogen. White LEDs, and HID beams, produce their light output in a very "spikey" manner - that is to say, if you visualise the colour spectrum on a graph, LEDs/HID will have only steep spikes at certain wavelengths, and emit very little light at others. The end result is still white, but you are missing colours inbetween. Halogen, on the other hand, produces a smooth output, with near 100% of colour emitted evenly, though trailing of a little at the blue end of the spectrum. LEDs are worst in this regard, with HID in-between, but this is where halogen comes into it's own.

What this means to the driver, is that while an LED/HID beam is nice and bright, things don't "pop out" as clearly.

The other aspect is colour temperature - to get the most light out of an HID beam, it needs to be at 4300k, for LEDs the most light is produced at 6000k. The disadvantage of these temperatures vs the 3XXXk of halogen, is down to the way our eyes process light. We have three kinds of vision (kind of - it's more of a scale really) - photopic (used in bright light conditions), mesopic (used in meduim light conditions) and scotopic (used in only the darkest of situations). These "modes" are as a result of the rods and cones we use to detect light in our eyes.



Rods are crude, with very little ability to distinguish colours, but they are able to process low levels of light well at the blue end of the spectrum. Cones recognise colours in great detail and we use them to see a wider spectrum, including longer wavelengths of red light, but they are poor in low light conditions. As a result of this, a higher colour temperature beam from LEDs/HID causes our eyes to adjust towards mesopic vision more readily due to the lack of red/orange/yellow light, and in doing so reducing our ability to recognise objects by colour gradients, and causing increased fatigue. This is the same reason that humans show a better ability to recognise a distinct spectrum within red-yellow, but find it harder to separate different tones of blue, and why the emergency services use blue lights.

The other factor, is that blue light refracts more on our retinas, than red or yellow, so higher temperature light generally results in more glare. It's for these reasons, than the French with their selective yellow headlights have always had better vision on poor weather conditions, and why yellow fog lights are of benefit.

The upshot is that halogen produces the best light for use by the human eye. It has low luminous efficacy (not a typo BTW), and takes more space, but given unlimited power, and space, it is the best light source. LEDs and HID come into their own when other practical reasons require it.

HTH Visiting from DISCO3.CO.UK
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