Lumen. Lumen is the amount of light a bulb or fitting generates. We used to buy our old fashioned incandescent/halogens according to Wattage, because a 50W Halogen or 100W incandescent was the same as any other 50W Halogen or 100W incandescent in terms of the quantity, and quality, of light they generated, we were all familiar with the light outputs we’d grown up with it.
LED’s are slightly different, power consumption or Wattage is no longer an accurate indicator of how much light a bulb or fitting generates. The amount of light one 5W LED bulb generates compared to another 5W LED bulb can vary considerably and this is where the inexperienced LED lighting buyer can get caught out by some LED manufacturers claims.
We often see LED manufacturers making ridiculous claims that their LED product is the equivalent replacement to a certain wattage incandescent bulb, be careful to check and compare the lumen output of the one versus the other irrespective of the power rating.
Lumen output is the new standard by which we should judge one light against another.
Lux. Lux is defined as the amount of light at a certain point. Lux levels can vary depending on how far you are from the light source and the beam angle of the light source. Let’s take two different lights that generate 1000 Lumen each, one is a normal bulb and the other a powerful laser pointer.
The bulb has to share it’s light in a 360 degree arc whereas the laser pointer is a fine directional light beam. The lux levels at any given distance will obviously be much higher for the highly directional laser pointer compared to the bulb which sent it’s light in all directions.
Beam Angle. The degree of directionality of the light, the more directional the light the smaller the beam angle. The Beam Angle is measured from the centre point of the beam outwards to the point where the light level drops below 50% of the light value at the centre of the beam. A bulb has a 360 degree beam angle and a laser pointer may have a close to zero beam angle. Down lights anything from 20 to 60 degrees normally.
Colour Temperature. Rated in K (Kelvin) This is the cooler of the light generated according to the chart to the right.
CRI, Colour Rendering Index. Every light source is characterised according to how well it shows colours. This is described by the Ra number where the higher the number the more accurately colours are shown. For the majority of indoor workplaces a minimum of Ra80 is required. For general outdoor lighting Ra70 is more usual. Increasing the Ra number to 90 or above generally comes at the expense of a reduction in efficiency.
Power Rating. Wattage, just like the older bulbs, LED’s also have a power rating of how much electricity they consume.
Power Factor. Power Factor is an indication of how efficiently the LED light utilises the power supplied to it. The higher the Power Factor is to a value of 1 the better.
Voltage. Like every other electrical device it must be supplied with the correct voltage, LED are normally available in 220V or 12V.
Dimmable. We all know that incandescents and halogens were fully dimmable. Unfortunately the dimmability of LED lights is a little more complicated. LED’s can be dimmable or non-dimmable, but even the dimmable LED’s may only work with an approved dimmer or range of dimmers.
We have seen cases where using “dimmable” LED’s with non approved dimmers damages the dimmer, the LED’s and sometimes both, in most cases they either do not dim at all or the LED’s flicker.
Lifetime. All lights, including LED’s have a Lifetime Rating, this is an indication of how long the LED should last before the light level output drops below a certain point, normally around 70-80% of the original value. Not when it fails completely. We have seen these ratings for LED’s vary from 25 000 hours to as high as 100 000 hours. Some of the ratings may be a little optimistic considering that 100 000 hours at 5 hours a day equates to just over 54 years.
This is a theoretical indication of how long the LED light should last under IDEAL conditions, real life is very seldom ideal, but they should last for many years under normal conditions.
Diffuser. Is any device that diffuses or spreads out or scatters light in some manner, to give soft light.
Luminous Efficacy. This is a rating of how efficiently an LED light, or any light source, converts electrical energy to visible light. This is described in a Lumen per Watt ratio.
We further have what we refer to as the Luminous Efficiency which is referred to as a percentage of the theoretical maximum Luminous Efficacy of 683 Lm/W.
As an example of where we currently are in terms of Lighting Efficiency our good old fashioned incandescent bulb offers a Luminous Efficiency of only 2-2.2% at 13-15 Lm/W, not very efficient at all, a candle is roughly 0.3%.
Current LED lights are around 4-14% efficient with a theoretical limit of 43.9% achievable, roughly 300 Lm/W, so we still have a way to go with LED Lighting before they reach their peak.
RGB. Simply stands for Red, Green and Blue, LED’s can be manufactured in any colour or even with all three RGB colours that enables the fitting to generate any colour under the rainbow simply by controlling how much of each colour is activated with the resultant mix generating any desired colour. (Colour Changing.)