Lumens, Watts, Lux – what does it all mean?
Since LEDs have been introduced into the market over 10 years ago there has been a confusing array of new terms and phrases to explain how much light they produce.
Following is an explanation of those terms, and a guide to help you avoid the pitfalls of low quality LED lights.
Terms: Watts, Lumens, Lux, Kelvin
4WD LED and HID Lighting
4WD Lighting Explained: Lumens vs Watts
Watts or Wattage is the current draw of just a light source or the whole lighting system: lights, loom, switches, circuit board and relays. Most often it refers to the lights themselves.
A light with 10 x 10w LEDs = 100W, but the other components (loom, switch, PC board, relays) will be absorbing 5 to 10% more power (in quality applications like ARB Intensity and Ultra-Vision), so the total draw will be 110w.
A common misconception is that LED’s ‘don’t draw much power’ and therefore any ol’ wiring will be good enough. 100W of halogen is actually the same current draw as 100W LED, so having a suitable wiring harness is important.
Another little known fact is that is some low quality manufacturers claim 100W (say 10 x 10W LEDs) but only run the LED’s at 3W to reduce the heat build-up and make them last longer. This means that the lamp is technically a 100W but it is only acting as a 60W. Some manufacturers have thermal management systems on the pc board, reducing power when the system detects high temperatures, but of course, this reduces light output.
Advances in optics and reflectors by good quality manufacturers has reduced their need to run high wattage LEDs, avoiding all the issues surrounding temperature control and thermal losses. (See below)
Lumen is the measurement of the output of a light source, related to the input power, and can be split into 2 groups:
Raw Lumens is the light output quoted by the manufacturer of the LED, usually at a nominal temperature ie, 25°C, which is not related to the temperature of operation. This is not ambient air temperature, it is PC board temperature. ie: a particular 10w LED may have a Manufacturer Raw Lumen figure of 1050 Lumens. If you have 8 of these in a lamp the Raw Lumens for that lamp is 8 x 1050 = 8400 Lumens Raw.
Effective Lumens is the actual measured Lumen figure that takes into account real losses e.g. Thermal loss, Optical Loss & Assembly loss.
ie: Thermal loss, Optical Loss & Assembly/Circuitry/Electronic losses, on good quality LED systems could be as low as 5 to 10%, eg: 8400 Raw Lumens = 7560 Effective Lumens. Poor quality lighting companies have up to 35% Lumen loss due to bad thermal designs, bad housing designs and cheap optics. The Effective Lumen output would be 5460Lumen, assuming the LEDs are at full wattage (see above).
Lux is the measurement of light at a specificpoint , position or distance from the light.
Lux is a world-wide term for the measurement of light on a specific surface. It requires the use of a Lux meter which measures the light output at that position. 1 lux of light is approximately equivalent to a full moon at night in good atmospheric conditions.
When you’re considering buying lights the first relevant measurement is the effective lumens, not watts. If a manufacturer doesn’t specify if the value is raw or effective, you can assume it is raw. Like engine power figures, specified at the flywheel or at the wheels. They won’t be telling you the lowest figure!
However, this is still not the complete story. Lumens need to be balanced with the Lux value, as lumens still doesn’t tell you how the light is controlled or should I say ‘focused’.
Having 10,000 lumens of uncontrolled light may give you a massive light ball up close but this will be useless driving at highway speeds.
The Kelvin (K) of a lamp refers to the colour output or colour temperature of the light produced.
There is no absolute standard for colour temperature. Within the range of halogen and HID/LED everyone has a personal preference, which is often influenced by the road surface, surrounding country side and weather conditions.
Traditional halogen light globes were on the lower end of the scale, from 2800K to 3500K. This is the yellow side of the colour spectrum and typically gives good definition at close range but has poor penetration. A decade or 2 ago, when halogen lights were popular, it was common to see driving lights with blue covers. This filtered the light to make it appear more white, some drivers observed to look brighter. However, the cover is a filter that absorbed light, giving it a whiter appearance, but even less distance.
With the introduction of HID’s and later LED’s, the colour scale moved up to 6000K to 6500K level (even 8000K), which is white to blue-white colour.
The severe flash-back of road signs, the ‘haze’ effect produced by the blue-white light and poor fog penetration has seen the market settle on lower Kelvins, 4000K-6000K range, which produces great penetration and ability to see detail. Just what you want for ‘Spot
Light ON’ driving.
Halogen globes are still common in OE headlights as they are cheap to manufacture, but produce a very poor light. Eg 70 Series Landcruiser!
HID replacements are very bright but typically unreliable. HID technology is now being overtaken by LED replacement globes and LED Driving Lights and Light Bars.
LEDs are significantly brighter than halogen, longer reaching and simple to fit, but are not legal in some states as a replacement headlamp globe.
The Ultra-Vision LED Headlamp Conversion is available for a wide range of bulb types.
Reflectors, Lenses and Focus
As light travels through the lens, it loses intensity depending on the clarity of the material. This is due to inherent internal material losses and to the loss as light travels from air through the lens back to air. These losses can vary from 5% to 20%. An open optic lamp will produce higher effective lumens as the light doesn’t have to shine through anything, but the reflector of the open optic has to be precisely focused to get the maximum result from the LED. A dirty, scratched or dull lens or reflector will greatly affect the beam of light.
There are 3 main types of optics used for Driving Lights, Light Bars and Work Lights:
- Open form Reflector
- Total internal reflection optic (TIR)
- Reflector with secondary optic
All 3 are used in different applications depending on the complexity of the beam pattern, number of LED’s and other factors.
Open Form Reflectors – Best For Driving Lights and Light Bars
Ultra-Vision mainly uses open reflectors in an open chromed pocket with a central LED design. These are usually in a circular pattern for driving lights and linear for light bars. The open form provides the maximum amount of output with only the lens detracting from it. High quality chroming on the reflector is necessary to achieve high Lux readings at distance, and the multiple, individual pocket reflectors give the opportunity to have pencil and spread beams in the one reflector. The Ultra-Vision Nitro Maxx has ‘Contrl’ optics for significantly increasing distance and ‘Widr’ optics providing 180 degree width.
Total Internal Reflection (TIR) optic
This type of optic allows designers to achieve a very complicated beam pattern and is best suited to Work Lights.
The TIR is circular or square and locates directly on top of the LED on the circuit board. The LED shines into the back of the optic and the light is controlled by the internal reflection of the plastic. A slight blemish or imperfection on the moulding will result in the light straying, which is acceptable in a Work Lamp application.
Different plastics and polymers have different properties, so as always, the optical performance is highly dependent on the quality control of raw materials.
Reflector with secondary optic
This method is commonly used in older or less expensive lighting systems and tends to be the least efficient of the 3 methods. There are inefficiencies in the reflector and TIR models and these tend to be compounded when put together. While it is possible to achieve good results with this method, the difficulty of aligning the LED, reflector and optic make it more likely for slight misalignment during assembly and even slight misalignment will have a significant effect on Lux readings at distance. Also, like TIR the quality of the materials used is very important and can affect the results by 20% if not managed well. Again, particularly noticeable at long distance, and is the reason most low quality LED lighting performs poorly at distance.
Intelligent optics and reflector technology has advanced to the point where good quality manufacturers like the ARB Intensity and Ultra-Vision ranges are able to achieve better light outcomes with smaller wattage LEDs.
The traditional view was that Driving Lights are for distance and Light Bars are for width. While this was true 5 years ago, it’s not quite so relevant now.
HID lights reach km’s down the highway, but the typical animal strike is from close in, animals hiding on the verge or close to it.
The combination of HID spotlights and LED light bar is a very effective combination, but the latest technology has resulted in Light Bars achieving 1Lux at 1.8km, and LED Driving Lights achieving 1Lux at 1.2kms. Virtually the same performance, so it’s really a personal choice more than a technical decision on whether to fit round LED Driving Lights or a LED Light Bar.
If you would like any further information or to discuss lighting options for your 4×4, please make contact with one of our experienced staff.
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