carbon trust green business fund 1 - LED Lighting FAQs

What is an LED?

An LED, or Light Emitting Diode, is a small piece of electronics that turns electrons into photons.

In other words, if you apply a voltage to an LED, it emits light.

LEDs are manufactured or ‘packaged’ in various ways and put into LED light fittings.

The exact method of manufacture determines the characteristics of the LED, such as colour temperature and luminous flux (brightness).

What is an LED

What is an LED driver?

An LED driver ensures the LED light fitting receives a constant amount of power.

The electrical properties of an LED can vary, for example with temperature, and the driver monitors this and makes sure exactly the right amount of power is delivered at all times.

LED drivers are often supplied as separate units which are then plugged into the LED fitting. In this way, if a driver were to fail, just the (cheaper) driver would be replaced, rather than the (more expensive) LED device itself.


What are Lumens?

The lumen-rating of a light basically tells you how much light is being emitted. If there are more lumens, the light is brighter.


For example, imagine two different 5-foot, 45W LED batten lights, as follows:

i) 5-foot, 45W LED batten light giving out 6,000 lumens, and

ii) 5-foot, 45W LED batten light giving out 4,500 lumens.

Both battens draw the same amount of power (45W), but the first one gives out more light than the second.

The first batten is able to deliver more lumens (6,000) because the LED chips inside are more efficient.

Technically, a lumen is an ‘SI unit’ like metres, Celsius, kilograms, and so on. Whereas a metre is a measure of distance, a lumen is a measure of ‘luminous flux’.

When you see either ‘luminous flux’ or ‘lumens’ on an LED data-sheet, you need to check whether these terms refer to the LED chip or the overall fitting.

For example, the LED chips in a light may have a luminous flux of 4,300 lumens, but the overall fitting might have a luminous flux of only 3,700 lumens. It is important to focus on the 3,700 lumens figure, as that is the actual amount of light coming out of the fitting.

Where are the missing 600 lumens? Most of these are lost as the light travels through the diffuser that sits between the LED chips and the observer.

Lumens are not to be confused with Lux.

LED Warehouse

What does Lux mean?

Lux is a measure of how well a given location is illuminated. For example, I am currently sitting at a desk and there are 450 lux on the desk surface (measured by a light or lux meter).

I have two lights shining on the desk and if I turn one of them off, the lux level goes down to 290 lux. In effect, my desk surface gets darker and I can’t see as well.

When designing LED lighting for a customer, you need to consider first what lux levels would be appropriate in each location, and then how to achieve those lux levels.

The Chartered Institution of Building Services Engineers (CIBSE) provides guidelines for suitable lux levels for a variety of applications (office work, engineering, warehousing, etc.).

If CIBSE recommends 150 lux in a loading bay, for example, you then need to use software, such as DIALux, to work out how to achieve 150 lux at the height staff will be working at, and taking into account factors such as the dimensions of the space.

Warehouse highbay LED lighting

What is the difference between Lumens and Lux?

Lumens and lux are often confused.

Lumens are a measure of how bright a light is, whereas lux tells you how well illuminated something is.

For example, an LED light attached to the ceiling at a height of 3 metres, giving out 5,000 lumens, might provide 300 lux on the surface of a table below. The table surface is at 80cm.

Let’s assume this is an ergonomic table which can be raised and lowered at the touch of a button. If we now raise the table surface to 120cm, the lux reading changes to 400 lux.

In other words, the table surface is now better illuminated – effectively there is more light – as it is closer to the LED light source above.

In this example, the lumens do not change – the LED always gives out the same amount of light – but the lux levels do change, as the table surface goes up and down. In rooms with windows, there are often major lux swings as the sun comes out, hides behind a cloud, etc. LED lighting is often supplemented by natural light from windows, and this effect can be controlled to a certain degree by daylight harvesting sensors.

What does ‘Lumens per Watt’ mean?

Lumens per Watt is a ratio which tells you how efficient an LED light is. It is a very important ratio to keep an eye on if you want to save money.

Consider two LED 600x600mm panels (the ones that fit into office ceiling grids):

LED A is rated at 26W and gives out 3,380 lumens. This means it only needs 26W of power to deliver the 3,380 lumens. LED A has, therefore, a Lumens per Watt rating of 130 (3,380 divided by 26).

LED B is rated at a higher 40W, but gives out the same 3,380 lumens. LED B’s Lumens per Watt rating is therefore 84.5.

The question to ask then is: if I need 3,380 lumens to light up my work space adequately, why would I install a 40W LED – which consumes a lot of power – when I can have those same 3,380 lumens for only 26W of power? The 26W LED will reduce my electricity bill by 35% compared to the 40W version.

40W LED panel lights are often sold because they are cheaper than more efficient LED panel lights with a higher Lumens per Watt rating. These 40W LED panel lights are, however, only cheaper at the point of sale. They end up being much more expensive when annual electricity savings are taken into account.

For the best overall cost of ownership, ask for LED lights with a high Lumens per Watt rating.

What LED colour temperature do I need?

A particular LED light fitting will often come in more than one ‘colour temperature’.

Colour temperature is measured in degrees Kelvin (K) and indicates how the light will appear to the observer.

For example, a colour temperature of 3500K will appear ‘warmer’ (think evening sun) than the ‘cooler’ 5500K (think mid-day sun).

When surveying a customer’s lighting, it is very important to select an appropriate colour temperature.

For example, a printing company might prefer a colour temperature of around 5500K so that when they look at what they have printed, the colours are ‘true to life’ and don’t take on a colour tone from the LED lighting.

On the other hand, staff working at an insurance company in an open plan office might prefer a colour temperature of a warmer 4000K. The cooler 5500K might be seen as too cold and impersonal.

To help customers appreciate the difference before they commit to a project, it is best to install fittings of two contrasting colour temperatures and let them decide which one they prefer.

Colour Temperature

Colour temperature ranges from extra warm white through to daylight

How long do LED lights last?

All LED lights have a predicted life-time stated in hours. 50,000 hours is quite typical. To make this number meaningful you need to work out how long your lights are on per year.

For example, let’s imagine a warehouse with racking which opens at 08:00 and closes at 17:00 each day. The warehouse is operational 5 days a week, and 50 weeks per year. That equates to 2,250 hours per year.

If you install LED lighting to illuminate the aisles between the racking and the LED lights have a life-time of 50,000 hours each, then each light is predicted to last 22.2 years. This number is reached by dividing 50,000 by 2,250.

If, on the other hand, the warehouse was operational 24 hours a day (instead of 8 hours), the LED lights would be on 6,000 hours a year. This would bring the predicted life-span of the LEDs down to 8.3 years.

LED Warehouse

 What are LED motion sensors?

Motion sensors fitted to LED lighting help you save even more money.

In some areas of your business, lighting will only be required if members of staff are actually physically present in that area.

For example, in a warehouse with 20 aisles, there is no point having all the lights on in all the aisles throughout the day, if staff members go to those aisles infrequently.

Motion sensors detect the presence of people and turn the lights on automatically. When the people leave that area, the lights dim down to say 20% and then turn off completely a few minutes later.

In this way, the LED lights are off most of the time, thereby saving a lot of money in electricity costs.

Motion Sensor

What is daylight harvesting?

A daylight harvesting sensor on an LED light allows the light output of the LED to vary automatically in relation to the amount of natural light coming into the room through the windows.

For example, on a grey day in an office with windows, the sensors might detect very little light coming in through the windows and keep the LED lighting at 100%.

However, if the clouds lift and the sun comes out, the sensor will detect a large increase in light and dim the LED fittings accordingly. In other words, with lots of natural light you don’t need as much LED light, and can save money by having those lights dimmed.

Daylight harvesting can be fine-tuned with the careful placing of sensors. For example, the LED lights near the window of an office might be dimmed to 20% when the sun is out, but the lights at the far side of the room might only be dimmed to 80%. The lights between these two extremes would be dimmed somewhere in the range of 20-80%. This creates a fairly uniform lighting distribution across the whole office.

Daylight Harvesting

Do LED lights cause glare?

Glare is a sometimes uncomfortable sensation that can be caused by lighting.

For example, if you sit at your desk and can see a light in front of you at a low level, it might cause you to squint or even give you a headache. This is glare.

However, that same light at the same distance in front of you, but much higher up on the ceiling, might not cause you any discomfort at all, as it is now out of your main field of vision.

In the first case the light was causing glare; in the second case, it was not. Glare is therefore partly a function of the light itself – how it distributes light into the space – but also the position and orientation of the light, as well as how the rest of the room is illuminated. Good lighting design helps avoid glare.

In addition, you can select LED fittings with ‘low UGR’ ratings. UGR stands for ‘Unified Glare Rating’. Generally, an LED light with an average UGR rating of >30 will cause a lot of glare, no matter how it is positioned. An LED light with a UGR rating of <10 will cause barely any glare at all.

In practice, LED lights with a UGR rating of <19 are considered ‘low glare’ and will perform well in most applications where glare could be a concern.

What is CIBSE?


LED lighting Solent Body Builders

Will LED lighting save me money?

Yes. If you upgrade your existing lighting to LED, you will notice a big reduction in your electricity bill.

For example, a typical 72W fluorescent ceiling panel light in an office would be replaced by a 26W LED panel.

If you have 100 of these fluorescent panels and they are on for 8 hours a day, 5 days a week, and 50 weeks a year – and assuming you pay 12p per kWh for your electricity – your annual electricity bill for these lights will be £1,728.

Switching to LED panels will reduce the annual bill to just £624. That represents an annual saving of £1,104 – a reduction of 63.9%.

Save up to 85% on your lighting bills

Do LED lights need to be serviced or maintained?

A traditional non-LED light comprises two parts: (i) the main device itself, and (ii) the bulb that fits into the main device.

If the bulb goes, you take it out and replace it with another one. As anyone who manages the lighting in an organisation knows, bulbs have a habit of failing fairly often.

An LED light, by contrast, does not consist of a main device and a bulb. An LED light is simply one unit that gives out light. In other words, there is no bulb to replace.

Fortunately, commercial LED lights typically have very long lifespans, which means your lighting no longer needs to be serviced or maintained, and there are no more bulbs to change.

What are the main advantages of LED lighting?

LED lighting products

With energy efficient financing, the money you save in reduced energy bills can cover the repayments of your new LED lighting

Energy efficient finance makes switching to LED lighting effortless as it simply funds the new lighting and installation. Then, the monthly finance repayments are repaid from the money you save in reduced energy bills – so no additional overhead.

It’s a great option for any size and type of business to switch to more energy efficient lighting at no extra cost and take advantage of all the benefits it provides.

Energy efficient financing

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