When we purchase LED downlights, batten lights, and ceiling lights, we always consider how many we need and how to calculate the quantity. Today, we are talking about it carefully; I hope I can help you understand more knowledge about it.
N =(Eva × A）/ （Φ xCU× K ）
N refers to the number of LED lamps.
Eva (Illuminance) refers to the luminous flux of visible light received per unit area. In layperson's terms, it is how bright it is per square meter. The unit is lux (lx) and 1lx=1lm/㎡
A (Area): A=length x width
Φ(Lumens per lamp fixture) refers to a lamp's total luminous flux value.
CU (The space utilization coefficient ) refers to the percentage of the light beam emitted from the lighting fixture that reaches the floor and work surface. Therefore, it is related to the design of the lighting fixture, the installation height, the room size, the reflectivity, and the lighting rate, which also varies accordingly.
K (Maintenance factor): refers to the factor multiplied by the decrease in light output capacity and the increase in the use time of the light source as the lighting fixture ages or the reduction of spatial reflection efficiency and illumination due to dust accumulation in the room.
| Area (Place) | Reference plane and its height | Standard illumination value Eva (lx) | UGR | CU | Ra |
| The living room of the residential building (general activities) | 0.75m horizontal plane | 》200 | 19 | 0.6 | 85 |
| The living room of the residential building (writing and reading) | 0.75m horizontal plane | 》300 should use mixed lighting | 19 | 0.6 | 85 |
| Kitchen | 0.85m horizontal plane | 》500 | 19 | 0.6 | 85 |
| The dining room of the residential building | 0.75m dining table surface | 》200 | 19 | 0.6 | 85 |
| General reading room of the library | 0.75m horizontal plane | 》500 | 19 | 0.6 | 85 |
| General office of an office building | 0.75m horizontal plane | 》300 | 19 | 0.6 | 85 |
| General supermarket business hall | 0.75m horizontal plane | 》300 | 19 | 0.6 | 85 |
| Hospital waiting room, registration hall | 0.75m horizontal plane | 》300 | 19 | 0.6 | 85 |
| School classroom | Desktop surface | 》300 | 19 | 0.6 | 85 |
| School classroom blackboard | Blackboard surface | 》500 | 16 | 0.7 | 85 |
| General corridor and flow area of public place | Ground surface | 》150 | 22 | 0.4 | 85 |
| Escalator of public place | Ground surface | 》150 | 22 | 0.4 | 85 |
| Rough machining of industrial building machinery | 0.75m horizontal plane | 》300 | 22 | 0.6 | 85 |
| General machining tolerance of industrial building machinery ≥0.1mm | 0.75m horizontal plane | 》300 should add local lighting | 22 | 0.6 | 85 |
| Precision machining tolerance of industrial building machinery <0.1mm | 0.75m horizontal plane | 》500 should add local lighting | 19 | 0.6 | 85 |
| Environmental pollution characteristics | Area (Place) | Minimum number of lamp cleanings (times/year) | Maintenance factor value（K） | |
| Indoor | Clean | Bedrooms, offices, restaurants, reading rooms, classrooms, wards, guest rooms, instrument and meter assembly rooms, electronic component assembly rooms, inspection rooms, shops, business halls, etc. | 2 | 0.8 |
| common | Waiting rooms, theaters, machining workshops, mechanical assembly workshops, farmers' markets, gymnasiums, etc. | 2 | 0.7 | |
| Severe pollution | Public kitchen, forging workshop, foundry workshop, cement workshop, etc. | 3 | 0.6 | |
| Outdoor | Awning, platform | 2 | 0.65 | |
Measure the length and width of the room in meters or feet to calculate the total square footage or square meters of the space.
Area=Length x Width
Determine the recommended illuminance level for the specific type of space(Eva). For example, offices typically require above 300 lux, while kitchens may need about 500 lux.
Total Lumens Required=Area×Recommended Illuminance Level (lux)
Choose the suitable LED lights with appropriate wattage and lumen output.
The lights' packaging or specifications should provide information on their lumen output per fixture.
In math, divide the total lumens required by the lumen output of a single LED light fixture to determine the number of fixtures needed,
N = Total lumens required / lumen per lamp fixture.
However, in practical application, we need to consider light reflectivity and utilization to use the CU(the space utilization coefficient ); in long-term use, we also need to consider dust-covered so we can use K (Maintenance factor).
So
N = Total lumens / (lumen per lamp fixture x CU x K)
Consider the distribution pattern of the LED lights and ensure that the fixtures' placement provides even illumination throughout the space.
Consider the room's layout, obstacles, or specific areas requiring more or less lighting. Adjust the number and placement of fixtures accordingly.
If you plan to have dimming capabilities, consider how this may impact the number of fixtures needed for different lighting levels.
If you're unsure about the calculations or specific lighting requirements for your space, it's recommended to consult with a lighting professional or an electrician for guidance.
The living room is 4 m wide and 5m Long. If I choose the 7W LED downlight, and the lumens per lamp are 700lm
How many of these downlights should I use?
First, we calculate the Square of the living room. A=4 x 5 =20 Square meter
Second, we choose the Standard illumination value of the living room Eva 200 lux, the CU value of 0.6, and the K value of 0.8
Third, Calculate the total lumens=20 x 200 =4000lm
Forth, N= 4000 / (700 x 0.6 x 0.8) = 11.9 so we choose the quantity is 12pcs
Finally, Evenly distributes these LED downlights
The illumination standards in different countries may be slightly different, and everyone has different brightness requirements, so the calculation will be slightly different. If you have any questions about LED lights, contact Top Sun Lighting, and we can discuss them together.
