Lighting plays a vital role in creating a comfortable and inviting space.

This is often determined in particular by three aspects of the light produced by the downlights or spotlights: 'Glare'; 'Flicker'; and 'Colour Rendering'.

In this article we will focus on Colour Rendering, which is a descriptor of how realistically colours are represented when illuminated by a particular white light.

This is intended to be an objective overview on the difference lighting makes to the atmosphere of a space. For more technical detail please visit one of our other articles: What is colour rendering and how is it defined?

What difference does Colour Rendering make?

The lights that provide the best Colour Rendering are often defined as 'Full Spectrum'; these often cost notably more than LED lights that provide better-than-average Colour Rendering. The difference you see is not necessarily in the light itself, but how inviting a space is. The right lighting can do this without drawing attention to itself; the room simply has a lovely atmosphere and everything looks & feels great!

Why does this make such a difference?

White light is formed of colours within the visible range of light. We perceive colours of an object by the colours that are reflected back, i.e. the colours that have not been absorbed by its surface.

When the spectrum of white light hitting that surface is not complete (which is often the case with LED lighting) it can flatten the appearance of objects and surfaces, making the space feel less dynamic and visually interesting. This is because the surfaces do not look as you would have expected, which can manifest itself as dreariness and a feeling discomfort.

For example, the red part of the visible colour spectrum is notoriously difficult to produce from LED light. This will adversely affect the appearance of surfaces containing red, including more obvious items such as wood floors and pink furnishings. Less obvious items like your white walls and grey curtains also contain red, which explains why their overall appearance looks starker and generally different to what you would expect. In addition to colours, textures can also be misrepresented under white light that does not have a full colour spectrum.

How can I tell if the lights I buy will provide good Colour Rendering?

Manufacturers provide the results of tests but there is no commonly used single figure that will accurately quantify how well the colours and textures of a surface are reproduced. There are two main tests which, combined, can provide a good indication of how realistic the Colour Rendering is:


CRI (Colour Rendering Index): Sometimes denoted as 'Ra', this is a number from 0 to 100; the closer to 100 the better the colour rendering could be. This only accounts for part of the visible spectrum and does not include ‘Deep Red’; primarily because it is very difficult to achieve a good result in. Therefore, a higher CRI does not always mean more realistic representation of colours under this light. Most LED lights will be rated with a CRI of 80 or above, with some reaching the mid to high 90s.

R9: This is the ‘Deep Red’ that is not included within the CRI results. Don’t be put off by apparently low figures of 50 or so! Most CRI 80 lights would have an R9 below 10, so the fact that R9 is even reported is usually a good sign. As with CRI, higher figures of R9 does not always mean a better representation of colours; it is simply an indicator (albeit a very good one!).

More detail on the types of tests that quantify Colour Rendering is provided in one of our other articles: What is colour rendering and how is it defined?

Colour Spectrum Graph

Many high-quality LED lights currently on the market will provide a graphic example of the colour spectrum; usually next to a typical example of better-than-average lights. Whilst this does little to quantify Colour Rendering, it can be an excellent way to see how realistically colours and surfaces are likely to appear under this light.

You will notice that on all colour spectrum graphs for LED sources used in lighting, the violet and red ends of the spectrum tail off. This is to avoid unwanted Ultraviolet (UV) and Infrared (IR) light, which is invisible to the naked eye.

In the example below, pay close attention to the shape of the two graphs, particular around the blue and red parts of the spectrum. The more realistic light closely follows the sun’s spectrum and will therefore provide a more pleasing environment.

Refurbishment of a Home

During the refurbishment of a 5-bedroom home, the cost of the project totals £500k (without including downlights). For example, the wooden flooring alone costs £20k and there are many other features that have taken time, money, and passion to select and install.

The project manager and the client all agree that the look and feel of the space is important, so they choose to use downlights with low ‘glare’. Selecting between 130 downlights costing a total of £4k or 90 downlights costing £12k, they have a choice between medium quality and the highest quality of light.

The highest quality lights would triple the cost of the downlight budget but, at a difference of £8k, it is agreed that it is prudent to install the highest quality lighting to maximise all the effort that has gone into the project.

Another factor not discussed here will have been the impact on the future; they selected the lights that are fully serviceable and come with a 20-year service guarantee, ensuring continuity of product in the long-term. In addition, there were environmental and sustainability factors, such as the ‘Cyclic Product’ policy of the manufacturer.

Energy Performance Certificate

Existing halogen light bulbs are being replaced with LED lighting prior to a follow-up survey. The sale or rent of the property is already secured, or viewings will be carried out during the day, so the look and feel of the lighting is considered less important than the budget. As a cost-saving measure, 100 downlights costing a total of £1k are purchased.

Lighting Project

A householder is installing downlights for the first time, in their 5-bedroom home. Selecting between 130 downlights costing a total of £4k or 90 downlights costing £12k, they have a choice between medium quality and the highest quality of light. Both options are for low-glare downlights.

After factoring the cost of install (£50 per downlight on this project), the total cost difference between the highest quality and medium quality light is £6k. Whilst they would like the highest quality light, the householder opts for the medium quality because £6k could be better spent elsewhere; they are saving towards an extension and full refurbishment in 3 years’ time.

Make the decision that best suits your needs

In conclusion, choosing ‘Full Spectrum’ lights with the highest available Colour Rendering will make the most of the spaces that they are lighting. When the install is part of a larger project, the cost difference is far less noticeable, and the lights will be a good investment. When the comfort level of the space is not important it may be more prudent to save money and opt for lower quality lights.

How can I get more help on the subject?

Contact d-lite at design@d-lite.co.uk for a no obligation chat or to arrange for a free lighting plan for your next project to be designed.

Click here to read the full article on our website.