Lighting plays an important role in today’s world. Whether at home, at work or in public spaces, proper lighting not only enhances the beauty of the environment, but also has a significant impact on people’s health, efficiency and comfort. But how can you accurately calculate the amount of light needed for each space? In this comprehensive guide from EDC, we will teach you how to calculate the light needed for a space and the formula for calculating the amount of light in a simple and practical language. By understanding the basic concepts and relevant formulas, you can easily provide the amount of light needed for each square meter and prevent wasting your capital and energy.
What is wattage?
The wattage, measured in watts, indicates the rate at which electrical energy is converted into other forms of energy such as light, heat or motion in an electrical device.
To better understand the concept of wattage, consider the following example:
Assume you have a 100-watt incandescent bulb. This bulb converts 100 joules of electrical energy into light and heat every second. Now, consider a 10-watt LED bulb. This bulb converts 10 joules of electrical energy into light every second.
As you can see, even though both bulbs produce 100 units of light (lumens), the LED bulb requires less electricity (lower wattage) due to its higher luminous efficiency (lumens per watt).
Why is it important to know wattage?
By choosing energy-efficient bulbs and optimizing your electricity consumption, you can significantly reduce your costs.
More importantly, electricity generation resources are limited, and using energy-efficient bulbs helps conserve natural resources and reduce environmental pollution.
Candela and Lumen: Units of Light Measurement and Comparison with Power Consumption
In the world of lighting, there are two common units of measurement for light intensity: lumens and candela. Each of these units has its own specific application, and understanding their differences is essential for correctly selecting light sources and calculating the lighting requirements of each space.
Lumen is a unit of measurement for luminous flux, or in other words, the total amount of light emitted from a light source per second. For example, a 100-watt incandescent bulb produces about 1,500 lumens of light. The higher the lumens of a light source, the brighter that light source will be.
Candela is a unit of measurement for the intensity of light in a specific direction. For example, a 10-watt LED bulb can emit 1,000 candela in its direct beam angle. The higher the candela of a light source, the more concentrated its light will be.
Difference between lumens and candela
| ویژگی | لومن | کندلا |
| سنجش | شار نوری (میزان کل نور) | شدت نور در یک جهت خاص |
| کاربرد | سنجش روشنایی کلی یک فضا | سنجش نور متمرکز یک منبع نور |
Difference Between Lumen and Wattage
Simply put, wattage is the amount of electricity a device uses per second. Note that lumens and candela are independent units and have no direct relationship to energy consumption (watts).
Comparing Lumen, Candela, and Wattage
| نوع لامپ | توان مصرفی (وات) | شار نوری (لومن) | شدت نور (کندلا) |
| ال ای دی 10 وات | 10 | 1000 | 1000 (در زاویه مستقیم) |
| رشته‌ای 100 وات | 100 | 1500 | 225 (در زاویه مستقیم) |
| سی اف ال 15 وات | 15 | 800 | 133 (در زاویه مستقیم) |
Note: Luminous efficacy (lumens per watt) is a measure of how efficiently a light source converts electrical energy into light. The higher the luminous efficacy of a light source, the less electricity it uses (the lower its power consumption).
We have covered everything you need to know about lighting parameters in detail in this article.
Light Output Per Watt
The table below shows the approximate luminous efficacy of different types of lamps:
| Lamp type | Luminous efficiency (lumens per watt) | Benefits | Disadvantages |
| LED | 80 to 150 |
|
Relatively high price |
| CFL | 50 to 80 |
|
Contains mercury (toxic) |
| String | 10 to 15 |
|
|
Let’s say you need 2000 lumens of light to illuminate a room.
If you use an LED bulb with a luminous efficacy of 100 lumens per watt, you will need a 20 watt bulb (2000 lumens / 100 lumens per watt = 20 watts).
While if you use an incandescent bulb with a luminous efficacy of 13 lumens per watt, you will need a 154 watt bulb (2000 lumens / 13 lumens per watt = 154 watts).
As you can see, using an LED bulb with high luminous efficacy reduces electricity consumption by up to 87%.
Standard light levels (lux) for common spaces
You can see the standard light levels for some spaces in the table below:
| Space | Approximate area (square meters) | Standard light level (lux) |
| Living room | 20 | 100 to 200 |
| Bedroom | 15 | 50 to 100 |
| Kitchen | 10 | 200 to 300 |
| Bathroom | 8 | 100 to 200 |
| Study room | 12 | 300 to 500 |
| Office | 15 | 400 to 500 |
| Store | 30 | 300 to 500 |
| School | 40 | 300 to 500 |
| Hospital | 30 | 200 to 400 |
Tips:
Surface color: Light surfaces (such as white) reflect more light and require less light, while dark surfaces (such as black) absorb light and require more light.
Ceiling height: In spaces with high ceilings, you need more light than spaces with low ceilings.
Presence of windows: If the space has natural light, you can reduce the amount of artificial light required to some extent.
Standard calculation of space light requirements
Calculating the space light requirements per square meter plays a fundamental role in creating a beautiful and safe space. By considering the needs of the desired space, the type of activity and the dimensions of the environment, appropriate light can be provided for each space.
Step 1: Determine the type of space and use
Specify the type of space (residential, office, commercial, industrial, educational, etc.).
Consider the exact use of the space (bedroom, study, kitchen, store, workshop, etc.).
Tips:
The amount of light required for each space varies according to the type of activity and its use.
For example, you generally need more light for studying or doing detailed work than you would in a bedroom.
Step 2: Calculate the area of the space
Calculate the area of the space in square meters.
For non-rectangular spaces, obtain the area using the appropriate formulas (triangle, circle, etc.).
Tips:
Accuracy in calculating the area plays a key role in determining the amount of light needed.
If there are unusable surfaces in the space, subtract their area from the final calculation.
Step 3: Determine the standard light level (lux) for the space
Use the standard light level (lux) tables for different spaces.
For example, the standard light for a living room is 100 to 200 lux. (It is fully stated in the table above.)
Step 4: Calculate the light loss coefficient
The light loss coefficient indicates how much of the light produced by the lamps reaches the desired surfaces.
This coefficient depends on the type of space, the type of lamp and how they are arranged.
The following values are considered for the light loss coefficient:
0.8 to 1: For residential spaces with ordinary ceilings
0.6 to 0.8: For office and commercial spaces
0.5 to 0.7: For industrial spaces with high ceilings
Tips:
Choosing the appropriate light loss coefficient prevents light loss and wasted costs.
If you do not know the exact light loss coefficient for the space, you can use the approximate values provided above.
Step 5: Formula for calculating the brightness of a space (lumens)
Use the following formula to calculate the total light required:
Total light (lumens) = Area (square meters) × Standard light level (lux) × Light loss coefficient
Example: Suppose we want to calculate the light required for a 20-meter living room with a normal ceiling. According to the table, the standard light level for the living room is 150 lux. We also consider the light loss coefficient to be 0.8.
Total light (lumens) = 20 (square meters) × 150 (lux) × 0.8 = 2400 lumens
Step 6: Choosing the right lamp
According to the calculations made in the previous step, you can also obtain the number of lamps required.
To do this, divide the total light required by the light efficiency of the selected lamp.
Example: In the previous example, we needed 2400 lumens of light and used LED bulbs with a luminous efficacy of 100 lumens per watt.
Number of bulbs = 2400 lumens / 100 lumens per watt = 24 bulbs
Summary
This guide provides a general method for calculating the standard lighting requirements for a space and a formula for calculating the brightness of a space. For more accurate calculations and specialized lighting design, you can seek help from lighting experts. EDC offers free design and calculation services to its customers. EDC experts will help you select and purchase the best lighting products according to your desired space and taste.
