What Is LED Lighting?
LED lighting is a solid state electronic form of lighting. Light output can vary from a very low power indicator light such as if often used to indicate if electronic items are operating, through to LED light fittings bright enough and of high enough quality to be used for illuminating premier League football grounds.
An LED is a diode made up of two semiconductors one with spare electrons, the other with a deficiency of electrons. The two semiconductors are connected by a junction. When a current is driven across the junction, light of a fixed wavelength (a single colour) is generated. This is actually very similar to the working principle of a solar cell, except in that case, instead of pushing electrons through the device to make light, the reverse happens and the device absorbs light which pushes electrons through the junction generating a current. Depending on the exact formulation of an LED, the light generated can be anywhere from the invisible infrared part of the spectrum through the visible colours to ultraviolet.
In order to generate white light from LEDs, there are two available methods.
Apply a coating of phosphors to the LED. The LED gives off light of a single colour which is absorbed by the phosphors and converted to white light.
This method can with the right mix of phosphors generate light with a colour rendering index CRI very close to that of natural light (sunshine), but at the cost of being slightly less efficient than a good LED light made with method 2. Note :- Incandescent lamps have a near perfect CRI but are a great deal more expensive to own and run.
If you have ever looked at an OLED TV next to a standard TV you will have seen how the former shows truer colours than the latter. That is the difference between a lamp with a good CRI and one that has not.
Mix light from several different LEDs of different colours to make white.
By omitting the phosphor conversion step, a very high energy to light conversion efficiency can be achieved, though often with a degree of compromise to the colour rendering.
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More on Colour Rendering Index
For general LED lighting, standard LED lamps are more than adequate with high efficiency, low maintenance, low operating temperature and modest prices.
For certain specialist applications where the quality of colour is of greater importance, high CRI lamps are recommended.
- Art Galleries
- High End Designer Homes
- Wedding Venues (lots of photos and videos)
- Fashion Shoots
- Film Industry (If you are spending millions on a feature film, it had better look right)
- Televised Sport
Colour temperature is a measure of white light based on the temperature to which you would need to heat an incandescent filament to get a particular shade of white. This “temperature” varies between around 1,700 K which would be referred to as Very Warm White and occurs naturally at sunset to around 6,500 K which is called Cool White and is seen in the middle of the day in overcast conditions. Paradoxically warm white if produced by an incandescent source is delivered by a much cooler filament than would be needed to achieve cool white.
Typically, white can vary from that which you get at noon in a high altitude desert – where the blue part of the spectrum is very strong to sunset where much of the blue light is filtered out by atmosphere leaving a redder shade of light.
Colour temperature has an effect on mood so that light with a higher colour temperature (bluish) is generally better for concentration, and a lower colour temperature (reddish) for relaxation.
It is generally preferred to go for higher colour temperatures in workplaces, sports facilities, kitchens and the like, (Typically around 4,000 K to 5,000 K) and lower colour temperatures in lounges, social spaces such as restaurants, and bedrooms, (typically around 2,300 K to 2,500 K).
For outdoor lighting, it is also recommended to choose a low colour temperature |(warm white) and to design the light fittings to light the desired areas with minimal spill over to surrounding areas. Warm white light with a reddish tint is generally considered less intrusive, less likely to disturb sleep and less disruptive for wildlife.
Unlike natural light and incandescent lights, generally LEDs have no ultraviolet light. Most of the time, this will not matter, but in a few specialist applications, ultraviolet light in suitable quantities is absolutely vital.
Vivarium and Aquarium Lighting
Anyone keeping snakes, lizards, or fish will need an ultraviolet component in their light as these creatures typically get much of their vitamin D through biochemical processes driven by UV. In addition, UV (enough, and not too much) tends to kill bacteria so lowering the risk of skin infections and such like.
Often birds are kept indoors for their entire lives. Birds secrete an oil a component of which on exposure to UV reacts to form vitamin D. This vitamin D is then ingested during preening. (The same process occurs in our skin). Without UV, this process does not happen, birds become deficient in vitamin D, their bones become brittle and they cannot be successfully raised.
The author was involved in a proposal to convert the lighting at a turkey farm from incandescent to LED – which would have resulted in huge electricity savings and a fast payback period. We specified high quality LEDs, and recommended that a small number of ultraviolet fluorescent tubes be left in. (UV LEDs are also now available, but not easily so at that time) The customer did not read our proposal properly, bought cheap LEDs rather than the ones we quoted, and ignored our recommendation to retain some ultraviolet lights – resulting in serious bird welfare issues, and a need to fit UV lights to fix the problem.
Specialist Growing Lights
These lights usually consist of a large number of LEDs in a panel. The LEDs are of a mix of colours, and a small number of ultraviolet LEDs. These are present primarily to facilitate deactivation of harmful bacteria.
UV Sterilisation and Sanitisation
UV light is able to rapidly de-activate or kill most bacteria and viruses, and is often used as a final stage of water or sewage treatment after settlement, aeration, and filtration. Using UV reduces the risk that treated water will produce a contamination risk. UV sanitiser lights are also available and can kill >99% of surface bacteria when shined on surfaces
Independent Chartered Surveyors
If you truly do want an independent expert opinion from a chartered surveyor, and many of us are also chartered builders, with regard to valuations, mortgages, mortgage companies, surveys, building surveys, structural reports/engineers reports/specific defects report, structural surveys, home buyers reports or any other property matters please contact 0800 298 5424 for a chartered surveyor to give you a call back.
Why Use LED Lights?
The primary reasons to use LED lighting rather than other forms of lighting are:
Superior energy efficiency
Typically LEDs use around 10% of the power of incandescent of a third of the power of fluorescent, high intensity discharge, or metal halide lamps.
Typically LED lamps last much longer than other types of light that they might replace.
Together these two advantages add up to a substantial reduction in annual cost of ownership.
LED lamps run cool with the surface of a typical LED lamp of decent quality maybe reaching 40C to 50C (or less) when operating. This contrasts to halogen lamps which in high power fittings can reach several hundred centigrade – hot enough to easily set fire to fabric if accidentally covered.(see below*) In addition, high power halogen lamps occasionally explode firing off very hot glass in all directions.
*The fire at Windsor Castle was caused by a workman's 1000 watt halogen spotlight setting fire to curtains. Had said workman been using an LED spotlight of around 120 W to 150 W – giving similar light output, this fire could not have been started by the lamp as it would not have got hot enough to ignite the fabric. The fire did damage costing £36.5 million to put right.
Not all LED lamps are the same
It should be noted that not all LED lamps are the same. Ideally for maximum efficiency and lamp life the following conditions apply:
- The lamp uses high efficiency LED chips from a reputable well known manufacturer.
- More LED chips than necessary are incorporated into the lamp which are then driven gently so helping the chips stay cool – e.g,if you want a lamp to deliver 10 watts worth of light and have an exceptional service life, don't use a single 10 W LED chip, use 5 x 10 W chips and drive each one at 2 watts.
- An oversized heat sink is used so that any heat given off by the LED chip is quickly dispersed. In the above example, even though the LED lamp is using 5 chips rather than 1 each running at 2 watts rather than 10 watts, the manufacturer might mount the chips on a heat sink rated for 5 x 20 watts.
- The driver (electronics powering and controlling the LEDs) is ideally separate and kept away from the LED so as not to warm the lamp. High quality electronics are used for maximum lifespan, and as with the LED, the electronics are over-sized and under driven so as to run cool and last long. Top quality drivers are also more efficient than run of the mill items so reducing the waste heat they give off.
- Good mechanical integrity – e.g. water and dust proof fitting made of robust corrosion resistant materials mounted on similarly robust brackets with corrosion resistant bolts.
For a regular LED bulb, some of these points are relevant, but not critical as a bulb can generally be changed quite easily at relatively modest cost – bear in mind however that in some situations such as changing a light bulb for a vulnerable resident in sheltered housing, it can cost half a day's pay or more to administer and carry out a light bulb replacement. Against such high maintenance costs paying an extra £1 to £2 per light bulb for better quality items designed for a longer life is a bargain.
Quality of LED lighting
Where the highest quality is absolutely vital is in situations which are safety critical, hard to access, or where a bulb or fitting is expensive to change.
Examples where the highest possible quality is justified – even at a substantially higher price are:
Aircraft navigation warning lights on Church steeples, telecommunications masts, and wind turbine towers. (Access for working at height can cost thousands before you even do any work, so ideally get lamps so over-engineered they won't need attention until your children are drawing pension! The extra cost is well worth it to avoid a service visit in a few years time.) In the most critical situations, consider fitting and separately switching duplicate fittings so that if a lamp fails, the spare can be switched on immediately without the cost of fitting a replacement item.
For street Lights, high bay lights, lighthouse lamps, airport runway lights, lights in operating theatres, and any other lamp with similar costly access or safety critical considerations, high quality is vital (In the case of airport lights special type approval is required).
How Durable are LED Lamps?
Depending on the quality of an LED chip, it will usually be rated at 50,000 to 100,000 hours of illumination at full brightness when mounted on a suitable heat sink and correctly controlled.
In LED fittings, lamp life is often shorter due to a limited life span in other parts of the lamp, or due to design compromises in the heat sink. (One of the main modes of failure of LED chips is overheating – with chip life tending to half for every 10C to 12C above optimal operating temperature.
Usually LED chips will be mounted on heat sinks designed to limit chip temperature to 75C or less with maximum survival around 150 C. Supposing you have an LED chip designed for a 50,000 hour operating life, and run it at 95 C, it may well only last around 12,500 running hours. Some consumer LED bulbs will have a design life of around 10,000 to 15,000 hours indicating design compromises in some aspect of the lamp.
At the premium end of the scale, top quality street lamps, high bay lamps, explosion resistant lamps for garage forecourts and similar will often have a design life of 100,000 running hours / 20 years or more.
In short, wherever possible, fit quality fit once!
One more small tip, for those managing property portfolios, it is suggested to find a good make and model of each commonly used light, and keep spares with your electricians. That way, if a lamp or components thereof need replacing, there's far less chance of supplementary work such as touching up paintwork to finish a job, or of having to leave site to get a compatible replacement.
Controlling LED lamps
LED lamps lend themselves far better to sophisticated controls than fluorescent or other kinds of light.
The following controls are used with LED lights
PIR / Microwave sensor lights
Lights are only on when a person is present, so allowing lights in areas not under constant use to be off for the majority of the time. A variant of this allows specially configured lights to switch between full and dim illumination typically between 100% and 10% brightness.
Take care to set the adjustable switches appropriately for:
- Ambient light levels – no point switching on corridor lights when the sun is shining brightly through the windows so set an ambient light level below which the lights come on when triggered.
- Sensitivity – you don't want your lights coming on every time a bird flies past the window, or a car drives past on the street so set the sensitivity to illuminate when useful with a minimal degree of false triggering.
- Illumination time – this needs to be sufficient time to meet the needs of users without leaving the lights on for too long unnecessarily.
Setting up dimming arrangements well can produce significant savings on a large development over the course of a year.
Tip – when setting sensors in very heavy traffic areas such as large under-croft car parks, bear in mind that LED lamps are not designed to survive an infinite number of switching cycles. This being the case, it is worth zoning the facility rather than having every light triggered every time, and setting the illumination time relatively long. If the lights stay on until the sensor has not detected anyone for 5 to 10 minutes, then they are likely to remain on continuously at busy periods whilst allowing energy savings at quiet times with considerably fewer switching cycles.
Example :- The author was involved in a lighting project in a large under-croft car park. The developers initially set the sensors for the car park lights for a short illumination period, however over a year or so, it was observed that a large number of LED lights were failing. On investigating, it was discovered that the LED tubes selected had a design life of 30,000 hours, or 40,000 switching cycles. With approximately 160 vehicle movements in and out of the car park each day, it turns out the lamps had been reaching the end of their design life in a far shorter time than expected (due to a very large number of switching cycles). The issue was resolved by setting the illumination period to 10 minutes, and zoning the lamp switching system - slightly compromising energy efficiency to preserve lamp life whilst still retaining a reasonable amount of savings when lamps switching off less frequently, but on average longer periods.
Many lights in housing developments, schools, and commercial / industrial sites serve a secondary emergency function.
When absence of mains power is detected, a built in battery module illuminates the lamp so as to allow for safe evacuation of the building. Typically, battery backed LED fittings are lit to about 10% brightness when running on the battery.
Systems are available for dimming LEDs which vary in sophistication from a manual dimmer switch to AI systems capable of dimming each light automatically according to how much ambient light is available at the lamp's location. Such systems can also be used for colour changing lamps used for light shows, stage lighting and such like which may in addition have a zoom lens on certain lamps to illuminate a varying sized spot.
Please note that setting up sophisticated lighting schemes is a specialist task, and it is not recommended that non-specialists attempt to undertake it. (The resulting errors can be time consuming and expensive).
Variable Colour Temperature lights
A few specialist high end lamps are designed with 2 or more white LEDs with phosphors selected to produce light at different colour temperatures. Such lights typically use a remote control to adjust illumination to suit mood – from bright cool white when concentration and alertness is called for, to dimmed warm white (red tinged to simulate sunset) for relaxation.
Unlike incandescent fluorescent and most other forms of lighting which shed light in all directions, LED chips give off directional light in a single plane. This can deliver a big advantage in efficiency over and above the inherent efficiency of the LED as far less efficiency is lost by light being absorbed in the fitting or emerging in directions where it is not useful.
LED light is especially effective in luminaires which need to deliver directional light as there is no need for reflectors of complex design to send light in the right direction – all that is needed is either a simple reflector, or a suitable lens and an LED lamp can deliver a beam of light of whatever shape and angle is desired. In LED street lights this can be taken to the next level to deliver a carefully shaped illumination pattern greatly reducing light spill over - making the most of efficiency whilst cutting unintended impacts such as disturbing neighbours and illuminating the night sky.
LED Lamp uses and Limitations
LED lamps are now available for nearly every application in every brightness, colour, beam angle etc. that you can imagine, and in a vast range of different luminaires. The only use case the author is aware of for which LEDs are not suitable is high temperature applications such as the interior of ovens.
We hope you have found this article useful
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