LED Due Diligence Questionnaire

With hundreds of lighting suppliers offering LED products 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 luminaire design. By understanding how much light the source produces and how much useable light leaves the luminaire it is possible to calculate the Light Output Ratio of the luminaire and therefore understand how much light and therefore energy is wasted inside the luminaire due to optical losses. Nearly all manufacturers now publish their data as absolute photometry making this less important and comparison between luminaires easier, the Light Output Ratio is stated as 100% and the lumen output of the complete luminaire is published.

By understanding the wattage and source lumens we can calculate how energy efficient the LED source is, this is important as there can be wide variations depending on the quality of the chip and driver used. It is important to request the system wattage which includes the electrical losses within the driver to ensure the figures are accurate and reflect the power consumption of the luminaire when installed, some manufacturers will only quote the LED wattage to make the product appear more efficient than it will be in reality. By dividing the source lumens by the wattage we determine the lumens per watt of the source. By dividing the luminaire lumens by the wattage, where Light Output Ratio losses are included as per point 1, we determine the 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.

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 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 and also specifies the maximum permissible UGR for most 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 do not include the required glare control to comply with this standard.

Another often overlooked requirement is for TP(a) fire retardant diffusers to be used in recessed luminaires when used in certain applications such as escape routes or when luminaires occupy more than a set percentage of the ceiling area. Again many lower cost products do not comply with these requirements and so are restricted on the applications they can be used in.

The quality of driver is essential to energy efficiency and lifetime, many low quality drivers have poor life expectancy, will consume more power than necessary and can also cause flicker of the LED source. Good quality European branded drivers typically offer 100,000 lifetimes and ripple current of less than four percent minimising flicker.

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

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 exterior lighting.

BSEN 12464 requires the use of 4000 kelvin colour temperature in the majority of indoors applications. Higher colour temperatures are often used as a method of cheaply improving energy efficiency despite giving having a high blue content 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 across batches of LEDs. 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 larger 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 but it pays to be wary of products where the colour spread is greater than this.

CE certification is legally required to sell a luminaire within the EU and as of 2023 the UK market will require UKCA certification, 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, predominantly 600×600 in size and suitable for lay-in installation in exposed T ceilings only. This can be challenging where a range of luminaire variants are required to suit differing ceiling types and installation methods to complete a project. A quality manufacturer will be able to provide a range of solutions, incorporate dimming, emergency and controls 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. The carbon footprint of a locally manufactured luminaire may well also be lower than one transported long distances. 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 itself. 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 at a fixed temperature and running current for a minimum of 6000 hours, from this information six times the test hours can be extrapolated to produce a TM21 lifetime estimate. 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 as to whether 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.

Companies should be asked to provide accreditations such as ISO certification to demonstrate they have quality and environmental certifications and commitments to carbon reduction and elimination of single use plastics should be verified.

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