A 4-Part Series to Clue you in Before you Buy
Week 2 – General Terminology
Welcome to week 2 of our 4-part series on cutting through the bunk and cluing yourself in about light bars and driving lights. In this instalment, we’re going to go over the general terminology that you’ll encounter when setting out to find the perfect light set-up for your 4WD.
The following are the ratings and measurements that you’ll see displayed all over the marketing material for your light bars and driving lights, and it’s vital to know what these values really mean.
The four terms we’ll look at today are:
- Lux
- Usable Light
- Lumens
- IP Ratings
Lux
Lux refers to how the light will illuminate what’s in front of you. It’s a measure of the intensity of illumination on a surface at a set distance from your vehicle.
What is 1 Lux?
1 lux is equal to 1 lumen per square metre (more on lumens later).
What you’ll read in descriptions is usually measured in lux units at a certain distance. For example, a light will offer ‘1 lux at 1km’. This means that your beam will illuminate an object 1km away to a brightness of 1 lux, or 1 lumen per square metre.
How Bright is 1 Lux?
To put this into perspective, 1 lux is the accepted amount of light needed for a person with 20:20 vision to be able to read a newspaper. So you’ll be able to read the paper a kilometre down the road; if that’s what you fancy.
Ways of measuring this value can vary, but lux values are generally accepted as a good standard measurement of how your lights will perform on the road. As a rule of thumb, if the lux levels are high but the lumens are low, your beam will be narrow. If the lux is low the beam will be wide, but won’t project far down the road.
Keep in mind that lux readings can be taken ‘on the road’ or in laboratory conditions. Readings taken on the road are more realistic, but also more difficult to get. A lab test will usually take a measurement at 25 metres in ideal conditions and then simply multiply the results to get a number for 500 meters or 1km, which means that in the real world the results may be very different.
Usable Light
Be wary of this term, it’s very vague. Lux is a real objective measurement, usable light is not.
Some companies will claim that 0.5 lux is a usable brightness, but this will depend on how good your eyesight is and what you are hoping to see.
With 0.5 lux of usable light, you’ll see a car 5 meters away without difficulty. However, you probably won’t see a kangaroo 50 metres away. While a usable light value doesn’t explain much in itself, it can be used as an objective reading of how far a light will shine when compared to other lights that display the same scale.
Lumens
Lumens refers to the amount of actual light that your light bar or driving light will produce. The thing to remember here is that ‘raw’ lumens and ‘effective’ lumens are two very different things.
The first thing to know is that the ‘raw’ lumens figure is basically useless to you and me. It relates to the how the LED can perform in optimum, factory-testing conditions. What we want to look at is the ‘effective’ lumens—how much light the lamp is producing based on how hard the electronics are working in the real world, taking into account factors like temperature and electrical current. A lamp that is running hot may only give off 50% of its potential power.
It is also important to note that how the light will actually perform when driving has a lot to do with how it is controlled. If the light is focused 100m down the road it will be very different to it a wide spread. Optics or reflectors will control how the light will actually spread. Don’t worry, we’re going to deal with optics in more detail in week four of this series.
All this means is that the effective lumens value is much more useful to you and me. It accounts for thermal losses, optical losses and the actual current that is being used. Be wary of manufacturers that don’t disclose an effective lumens figure.
One thing to keep in mind is that as this technology improves, light is controlled more effectively by the use of those clever optics that we’ll look at later. This means that overall lumen values are starting to decrease. This is why using lumens as a deciding factor for which lights to buy is dangerous—a lux value is a much more accurate indicator of performance.
IP Ratings
IP stands for ‘Ingress Protection’, and is an international standard measurement of how well an electrical enclosure can keep out ‘foreign bodies’—in this case, dirt, dust and water.
IP ratings are displayed as the letters ‘IP’ followed by two numbers, each one of which has a meaning. The first number is the level of protection from dust and debris, the second is the level of protection from moisture. Simple as that.
Common values that you’ll see here on light bars and driving lights are IP67 and IP68. IP67 means that the light is dustproof and capable of withstanding water immersion up to 1m deep for 30 minutes. The difference with IP68 is that is capable of withstanding water immersion up to 3m deep for 30 minutes.
In practice, we don’t expect your 4WD to be 3 metres under-water for over 30 minutes (we hope not anyway!), so a rating of IP67 is more than enough. Something to double-check here though is that the lights will be able to sustain pressure washers at close range. Look out to see if the manufacturers have a disclaimer against this, as many do.
Another factor to keep in mind when submerging your lights is temperature. Crossing a river when your lights are hot can cause aluminium housings to contract and allow water to enter through the seals. Even if this doesn’t happen, condensation can be a problem, despite a lamp being totally watertight.
Don’t worry though, there’s a solution to that—the breather valve. And luckily that’s the first thing we’re going to look at next week in part three of the series, which is all about the construction of the light and how you attach it to your 4WD. See you there!