Retail Lighting Design Education
Lesson 3: Retail Lighting Standards
This is a 24 hour tutorial on how to do a retail shops lighting design. The series of tutorial comprise of both theory and hands-on. Videos, PDF, and sample files are available for download.
Retail Lighting Design Standards
If you can read this, there is light. - Olafur Eliasson
There are different organizations that set design standards for lighting, and the design will then depend on the region or country in which it is located. Most of the standards refer to the local situation.
For this application, we will focus on the guidelines for following:
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Lux Level
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Overall Uniformity
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Glare
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Light Effect
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Color Rendering
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Color Temperature
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Sustainability Standards
There are also local standard requirements, like Shopping Mall requirements or Municipality requirements. The standards we will discuss focus on international requirements.
We will use the most popular lighting guidelines: the CIBSE and IESNA. If you are working with retail projects that have local requirements, then that local requirement must prevail, or sometimes whichever is more stringent.
It is best to ask the client in the early stages which standard to follow before you start working. If they don’t know, then check your country about the default guidelines. For example, here in the UAE, we always follow the EU standards due to the big influence of Europe on this country. Some projects that we have handled have US requirements, but that is very rare.
Below is an image from the IESNA Lighting Handbook. It shows the most important design factors for retail lighting.
The key is very obvious, the dot legend signifies how important each requirement is. A red dot is very important, half blue is important, and the empty green dot is somewhat important.
When you are using this dot matrix, make sure you double check that it agrees with the branding. If not, follow the branding lighting requirements. This is just a basic guideline.
In the next chapter, we will discuss more detailed explanations of the requirements for each factor in every area.
The guideline above shows how the Color Rendering Index (CRI) and Correlated Color Temperature (CCT) are very important in display areas, while Glare is important for cashier areas. Circulation areas don’t need much attention, but for some retail shop circulation areas need all these important points.
Check this video to learn about the Lighting Standard for Retail from IESNA Lighting Handbook. You may also download the PowerPoint presentation and the PDF chapter extracted from the book. Enjoy reading!
Lux Level
What is Lux Level? Obviously, as a lighting designer, these words are the most basic information you must understand. Dude, you cannot become a lighting designer if you don’t know this.
For a formal definition, see below. This is from our supportive friend, Mr. Wikipedia. You may find the similar definitions from other books.
The lux (symbol: lx) is the SI unit of illuminance and luminous emittance, measuring luminous flux per unit area. It is equal to one lumen per square meter. In photometry, this is used as a measure of the intensity, as perceived by the human eye, of light that hits or passes through a surface.
There will be more terms that you need to understand, such as the difference between luminance and illuminance, candela, luminous flux, etc. The more terms you know, the more conversant you are. Find the definitions here, http://lowel.tiffen.com/edu/glossary/.
The desired light level or lux level will depend on the brand requirements. But, if the client doesn’t know what the lux level should be, then you can use the SLL Code for lighting as your basic guidelines. As per this Code, Sales area must have at least 300 lux with 22 UGR and 80 CRI. Please explain these numbers to your client, tell a story to help them visualize the numbers. I remember one client who asked what 20 lux looked like. Hahaha! I was amazed by his question because I kept saying we should achieve 20 lux, and then suddenly he asked about it. I told him; ”Imagine you are walking on a major roadway with no buildings on either side”. He just said, “I see”, looking not so convinced. So, I pulled out Mr. Wikipedia’s table (see below) and he said, “OK”. Again, you must psychologically analyze whether he really understands it or not.
For Till Area or Cashier Area and Wrapper Table, we need to have 500 lux, 19 UGR and 80 CRI. This area may seem to need more light, but the current trend is for the highlighted merchandise to need more light and cashier area is sometimes lighted similar to general areas.
But then again, CIBSE has a note saying these illuminance and UGR will be determined by the type of shop, and the illuminance values may be varied to suit circumstances.
Most of the retail shops that we designed require at least 700 lux in general areas, 1500 lux at the entrance and 2000 lux on the merchandise. These may seem too much, but this is what the client wanted the shop to look like and they have their own reasons. SLL did not mention the overall uniformity. But, some of the retail shops we designed asked for at least 0.50 oU in general areas (with objects inside). What???! Amazing, right? How can we do that? That is one of the secrets you will learn from this e-book. As per our previous topic, we must ask our clients for this basic information before starting work on the lighting design.
Beside are some recommendations for retail applications.
Recommended Illuminance for Retail Applications
The table above is another recommendation from the IESNA Lighting Handbook, 8th edition. The conversion of foot-candle to lux is 1 fc = 10.7639 lux. You may use this table if your client is US based or if their unit preference is in foot-candle. Well, we need to adjust ourselves from time to time.
Overall Uniformity
What is Overall Uniformity? It is the ratio of minimum illuminance to average illuminance on a surface. If you are familiar with the Dialux software, here is what it looks like. (See image below)
The example above is for Office Application. However, for Retail Lighting Design, uO can be properly evaluated using the Pseudo Color because of the objects used in the calculation. Please note that you need to include the objects like gondolas, shelves, mannequins, etc. in your calculation because it is the only way you can properly judge if the spotlight is targeting the specific object or the track-lights really do reach the shelves on the wall, or the overall general area has enough light. It will also give you the correct values when the contractor or installer asks for the aiming diagram.
When you take uO in the retail shop calculations with objects inside it, it will give you poor results due to the fact that some areas will give 0 lux value because of furniture blocking the calculation surfaces. So, it is better to judge it using pseudo-color. In the next chapter, I will show you some of our presentations to evaluate the lighting design results for retail applications. Meanwhile, see the image below to see how the pseudo-color looks in a retail shop with good uO and with objects included. You can instantly identify if the merchandise is properly lighted.
This image used the standard pseudo-colors, although the value changes. For this example, the minimum color value is 400 lux (purple) and the maximum is 3500 lux (white). This shop has a light ratio of 1:15, it has theatrical effect.
As per the SLL Lighting Handbook, regardless of the shop’s profile, general lighting should be uniform, at least 0.70 overall uniformity (uO). But of course, you can only achieve this in the lighting calculations if you remove the objects and you dim down or turn off the decorative luminaires.
If you really want to show the 0.70 uO to your client to comply with the code, then, just remove the object and turn off some decorative lights. But, most of the time, having 0.70 uO is for big box retail shops and non-specialized outlets only. If they really do insist, then follow my instructions above. Always keep them happy. Wink!
Glare
What is Glare? We have two kinds of glare: direct and indirect. Direct glare is caused by bright areas, such as luminaires, ceilings and windows that are directly in the field of view. Indirect glare is caused by light that is reflected to the eye from surfaces that are in the field of view - often in the task area.
Glare might seem like a subjective term, but it is actually calculated using a precise formula. Essentially, this formula measures the luminance of a lamp divided by the background of visible luminance from the room. This number is called the Unified Glare Rating, or UGR, and it ranges from 5 to 40.
Although we really want to show off the merchandise by focusing more lights on that object, (maybe, we want a little sparkle), we still need be careful about the glare it creates for the customers. We don’t want customers to leave the premises with a head-ache. We want them to come back again and enjoy a pleasant experience inside the store; we want them to be happy and comfortable, at least with lighting aspect. Below is an image that may cause glare to the customer.
Spotlights must not be aimed more than 20 degrees towards the area where the customer usually stands. You can go more than that if it is aimed towards a wall or another area that doesn’t have people passing by or standing. This is critical in display windows where there is no back wall. You might get the right effect on the display window, but it may create glare to the customers inside the store.
