How many lumens per square foot retail store?

2023-09-14

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Candela & Lumen (Cd & Lm)
The unit of light intensity is candela, which is based on the intensity of ordinary candle light, but is now defined as 1/60 of the light emitted by a black body radiation of 1 square centimeter at the solidification temperature of platinum. A light source is uniform in all directions. Emitting 1 candela of light means emitting 12.3 lumens, that is, emitting 1 lumen per unit solid angle. Lumen is the unit of luminous flow.

Illumination (Lux)
The amount of light spread on an acting surface is called illuminance. Expressed in lumens per unit area. One lumen per square foot is the amount of lighting placed one foot away from the surface of action with one candela. Sunlight from a clear sky during the day is about 1,000 lumens per square foot. On a well-lit dining table, it is about 20 lumens per square foot. The corresponding metric unit is lux, which is 1 lumen per square meter. 1 lumen per square foot is equal to 10.76 lux or close to 10 lux.
In the United States, footcandles are used instead of US lumens per square metre, while the UK uses the latter to be identical. Lux is used in European countries.

Reflection coefficient
When light falls on a surface, it is reflected according to the properties of the surface. This property is called surface reflectance. The reflectance of a white surface is close to 100%, while the reflectance of an asphalt road is only 10%. The brightness of an object's surface is related to the illumination on it. For example, if a surface with a reflectance of 100% is illuminated by 10 footcandles, its photopic value is 10 foot-lamberts. The equation can be written as:
L=ER---(1)

Among them, L is the photopic degree in feet-lamberts, and E is the illuminance in foot-candles. R is reflectance, expressed as a fraction of one. Using metric units, the unit of L is apostilb (1 apostil equals 0.0001 lambert) and the unit of E is lux. Equation (1) only applies to perfectly diffused surfaces and does not apply if the surface has a shimmering sheen that may or may not be visible to the eye.

What are the lighting requirements for retail store?

Typical lighting levels for grocery supermarkets range from 750 to 1000 lux. The color rendering level for grocery stores can be at least Ra ≥80 for general lighting and Ra ≥90 for accent lighting and Fresh areas. The brightness level of light sources should not exceed UGR <19.

As shown in the figure below, LiteHome's Linear track lights are used in supermarkets to achieve an average ground illumination of 450lux while meeting UGR<13. This is a very good performance for a retail space.

UGR<13 Retail lighting

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