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LED definitions and standards

By Mark Allen, 21 May 2019 Electronics & Gadgets

4x4 LED driving light comparison test LED definition and standards feature

Lumens? Kelvin? Shining a light on LED jargon.

LUX is the International System unit of luminance (brightness), defined as the amount of light on a one-square-metre surface, all points of which are one metre from a uniform source of one candela of light.

LED DRIVING LIGHT TEST: 10 lights put under the spotlight

The higher the lux, the brighter the light is on the subject; whereas lumen (which is more often quoted by the manufacturer) is the total amount of light that can be generated by that light source. So, a 10,000-lumen light may throw a light which is measured at 500-lux 20m away, but that same light may fall to 10-lux at 600m away. 

Raw lumens is the ‘theoretical brightness’ an LED chip will output in controlled laboratory conditions, while effective (or actual) lumens is what the driver is left with once the LED chip has been packaged into a light housing, covered by a lens and filtered down by a wiring loom as well as other thermal and optical losses.

Generally, high-powered LED driving lights have three factors that cause the effective output to differ from the raw output: thermal efficiency (the hotter the LED, the less light produced), electrical efficiency (wiring loom effectiveness) and optic efficiency (the amount of light lost with the addition of optics – covers, lenses and reflectors).

Kelvin is a temperature scale used to measure the colour of light: the lower the temperature, the more yellow the light is; the higher the temperature, the more blue the light appears. LEDs are generally up around the 5000 to 6000K. Keep in mind the colour (or Kelvin) has no correlation to brightness.

4x4 gear: Halogen v HID v LED driving lights comparison

The 50,000-hour lifetime that is bandied about by most manufacturers comes from the LED manufacturing companies and not the driving light manufacturing company. The lighting engineers have accumulated data to prove an LED will last at least 50,000 hours of use and still produce at least 70 per cent of its original lumen (brightness) or 30 per cent depreciation; although, the actual LED never actually burns out.

High-powered LEDs don’t generate too much heat, but they are susceptible to light degeneration if subject to high working temperatures of (about) 30 to 40°C, which is why nearly all high-powered LED driving lights feature so many fins (or flutes) or heat syncs to help dissipate heat.

As far as dissipating that heat via heat syncs (an easy way of increasing surface area to let heat ‘soak’ out), the other way is via use of an aluminium housing. Aluminium, being a better conductor of heat than plastic, is why almost all high-powered LED driving lights are manufactured from aluminium (either cast or extruded) casings.

When it comes to a light being water- and dust-proof, the IP ratings are pretty straightforward. The letters IP stand for ‘Ingress Protection’ or ‘International Protection’ rating, while the numbers are split into two sections. The first is a numerical digit from 0 to 6, with 6 being the highest (or best) for rating against the ingress of solid objects like fingers, rocks, sand and dust. The second numerical digit from 0 to 9 is the rating against ingress by liquids for a certain amount of time to a certain depth or pressure. The higher the number, the longer and deeper the light can stay submerged.

In the below panel are the top ten IP ratings 4x4ers and campers would expect to see in advertising blurbs.

IP Number First Digit – Solids Second Digit – Liquids
IP60 Protected from total dust ingress Not protected from liquids
IP61 Protected from total dust ingress Protected from condensation
IP62 Protected from total dust ingress Protected from water spray less than 15 degrees from vertical
IP63 Protected from total dust ingress Protected from water spray less than 60 degrees from vertical
IP64 Protected from total dust ingress Protected from water spray from any direction
IP65 Protected from total dust ingress Protected from low-pressure water jets from any direction
IP66 Protected from total dust ingress Protected from high-pressure water jets from any direction
IP67 Protected from total dust ingress Protected from immersion between 15 centimetres and 1 metre in depth
IP68 Protected from total dust ingress Protected from long-term immersion up to a specified pressure
IP69k Protected from total dust ingress Protected from steam-jet cleaning