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More 'K' - 'Kelvin' - isn't necessarily better.

Ever since LEDs entered the driving and camping light world we’ve seen manufacturers quoting ‘K’ – ‘Kelvin’ -numbers as vital attributes of their products. More ‘K’ isn’t necessarily better.

We chose two identical Ultra Vision Nitro Maxx 155 light bars to examine the characteristics of a 4000K-rated LED bar, compared with a 5700K one.

We used the same HiLux test mount, on the same stretch of bitumen and gravel road, on the same moonless night, with only 15 minutes separating the two test drives. We filmed the runs, using the same Nikon camera at exactly the same exposure and zoom settings.

But first, here’s a brief explanation of why we did the test.

It’s easy to get confused by light technology and that’s why we’ve done a comprehensive story on this website explaining the various terms: lux, lumens, watts, amps and ‘colour temperature’ in K or Kelvin numbers.

Colour temperature is by far the most confusing of all light statistics, because it compares the Kelvin absolute temperature scale with the visible light spectrum.

William Kelvin was a physicist in the late 1800s and developed a temperature scale, using Absolute Zero (-273C) as its starting point, hence eliminating the minus numbers you get if the freezing temperature of water is used as the starting point.

Scientists welcomed the Kelvin Scale, because calculations are much easier to do without minus numbers.

The same bloke heated a piece of carbon, noting that it changed colour as its temperature rose: dim red, bright red, dim yellow, bright yellow, yellow-white, bright white and blue-white. Kelvin temperature points were later added to colour-temperature charts.

Back in the days when light brightness was a function of induced heat – making a filament glow bright yellow to white hot, but stopping short of melting it – the scale had relevance.

Back then, the higher the temperature, the whiter the light, but now there are cooler light sources – gas discharge (HID) and light emitting diodes (LEDs) – it’s plain confusing.

Checking out a colour temperature chart, it’s obvious that if you evaluate an HID or LED light purely on its colour temperature, more isn’t necessarily better.

The ‘sweet spot’ is in the 4000-5700K region, because higher numbers give too much ‘blue’ cast and head for eventual darkness at the end of the visible spectrum.


Nitro Maxx 155 evaluation

The two light bars had identical power, but the difference in Kelvin rating was immediately obvious: the 5700K bar was brilliantly white, with a faint bluish cast that was noticeable at the extremity of the beam distance and 4000K bar had more yellow light – much like a high powered halogen light.

The accompanying video clearly shows the difference in colour.

At first glance the 5700K light bar seems to be the most effective, with more detail at the outer edges of the spread beams and with slightly better distance penetration. But the more yellow light of the 4000K bar reflects far less from road signs and roadside reflectors, as well as from light fog patches.

Also, the ‘night blindness’ effect of flicking down from high beam with driving light to low beam is much less in the case of the 4000K bar.

Our assessment is that if your route involves reflective road signs and the need to drop down from high to low beam frequently, you’re probably better served with the 4000K option than the brighter 5700K.

If you’re travelling for long periods on high beam and you want maximum distance and spread brightness the 5700K option is the ticket.

Check out our video and see what you think:




























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