LED Due Diligence Questionnaire

With hundreds of lighting suppliers offering LED products available from around the world how can you be sure you are purchasing a product that will give you the quality of light, durable long term performance and the energy reduction that you require to justify the investment?

Comparisons between manufacturers products can be difficult due to a lack of standardisation in publication of performance figures making the purchase of LED Lighting a daunting process for those of us who are less familiar with the technical aspects of LED Lighting.

To simplify this process we have composed the following questions that any diligent customer ought to ask their supplier before going ahead with a purchase. We can provide detailed answers to all of the following questions about any LED products in our range and are happy to be open and honest about any performance criteria and testing that we have undertaken.


The intention of this question is to determine the efficiency of the optical design of the luminaire.

By understanding how much light the source produces and how much light leaves the luminaire it is possible to calculate the LOR (Light Output Ratio) of the luminaire and therefore understand how much of your energy input is being lost within the luminaire.

Many suppliers now publish “absolute photometry” where source lumens are not provided, only luminaire lumens, this is a perfectly acceptable approach however means LOR will equal 100% making comparison more difficult with those using traditional photometric methods. We can however still calculate the luminaire efficiency in this situation using the method listed in question 2.

By understanding the wattage and source lumens we can calculate how energy efficient the source is, this is important as there can be wide variations depending on the quality of the chip and driver used.

Some suppliers may only quote the LED wattage which is misleading, it is important to request the system wattage which includes the electrical losses within the driver to ensure the figures are accurate to the power that will be consumed by the product when installed.

By dividing the source lumens by the wattage we determine the lumens per watt.

By dividing the luminaire lumens (where LOR losses are included as per point 1) by the wattage we determine luminaire lumens per circuit watt.

Luminaire lumens per circuit watt gives the best measure for comparison of efficiency between different manufacturers luminaires and takes into account both the efficiency of the driver and chip as well as the efficiency of the optical design.

Even where absolute photometry is used luminaire lumens per circuit watt can be used to make accurate comparisons between manufacturers.

A photometric file will demonstrate that the product has been scanned in a photometer, will allow the creation of lighting schemes through programmes such as Relux and Dialux and will demonstrate that the manufacture has tested the optical efficiency and distribution of the luminaire.

If this data is unavailable it strongly suggests that the supplier has not been thorough in testing both the performance and efficiency of their product.

BSEN 12464 requires that the candelas per meter squared from the luminaire do not exceed 3000 above 65 degrees in applications where monitors are in use, this is to minimise glare on the screen and prevent visual discomfort.

Compliance with this standard is essential in applications such as offices and schools yet many low quality products disregard this requirement.

The quality of driver is essential to energy efficiency and lifetime, many low quality drivers have poor life expectancy and will consume more power than necessary.

As with the driver, a poor quality chip will be inefficient with lower lifetime than one from a reputable manufacturer.

Colour Rendering Index determines how well the human eye can determine the colour of objects lit by the source.

The majority of applications require CRI of 80 or greater with the exception of less colour critical applications such as warehousing and exterior lighting.

BSEN 12464 requires the use of 4000 kelvin colour temperature in the majority of applications.

Higher colour temperatures are often used as a method of cheaply improving energy efficiency despite giving a blue coloured light that is not ideal for many applications.

5000 kelvin and greater products are commonly used in far eastern markets but are not suitable for the majority of applications in the UK.

Because of the method by which LEDs are manufactured large colour variations can occur.

These different colours are separated into colour bins to ensure that colour consistency can be achieved by LED module manufacturers.

The wider the colour bins a manufacturer is willing to use the lower their costs become hence low quality products tend to have large colour fluctuations.

A one step Macadams Ellipse defines an area in the colour spectrum where the human eye can only differentiate a single colour.

The majority of luminaires are designed to mix the chip colours allowing a slightly wider range of colours to be used to ensure that products are economical to manufacture, therefore a three step Macadams Ellipse is typically deemed to be a good quality bin selection.

Be wary of products where the colour spread is greater than this.

CE certification is legally required to sell a luminaire within the EU, always demand that any supplier provides evidence that their luminaire has been tested in accordance with all applicable standards to ensure that it is electrically and thermally safe and compliant with EMC regulations.

Low cost products are often imported in large volumes in the most commonly used variants.

This can be challenging where a range of luminaire variants are required to complete a project but a common appearance is required.

A quality manufacturer will be able to provide a range of solutions and often customise products to your exact requirements for reasonable quantities.

A local manufacturer will typically be able to deliver faster and support your after sales requirements more effectively than one based abroad.

Ensure the product is fully manufactured in the UK and not simply imported and relabelled, if in doubt request a visit to the factory to witness production first hand.

Always consider the additional costs of an investment in lighting such as delivery and disposal of old product, a manufacturer who can support you in these aspects can make a significant difference to your overall project cost.

Many suppliers are now offering lengthy warranties with their products however the underlying terms and conditions can vary greatly.

It is critical to check the level of cover provided, whether it offers both parts and labour or replacement product only as the cost of installation is sometimes greater than the luminaire cost.

Some suppliers will advertise long warranty periods however these may only be available at substantial additional cost.

LM80 is an internationally recognised testing standard to verify the lifetime of LED chips.

LEDs are tested under worst case scenarios of temperature and operating current for a period of 6000 hours, from this information the 50,000 hour failure rate and lumen depreciation of the LED can be extrapolated with reasonable accuracy. Because of the duration of the test it is costly to undertake and therefore generally only available with the better quality chips on the market.

Proof of testing and evidence of failure rates and lumen depreciation provide important evidence that the product is likely to last for the duration of the warranty and that the manufacture has been diligent in the development process.

Lengthy warranties are now being offered with some luminaires on the market however it is important to establish if the company is likely to be operating throughout the warranty period in order to be able to support their product.

Less scrupulous operators may offer warranty periods which are unrealistic to provide themselves an advantage over the established competition with no intention of remaining in business for the duration of the warranty leaving their customers with faulty product and no recourse for repair once they have ceased operating.

It is also helps to establish that you are dealing with a specialised lighting supplier with the expertise and knowledge in the product to support you rather than a company from another sector that has launched an LED offshoot to take advantage of the growth in LED technology.

(+44) 01747 858100
(+44) 01747 858100