What is light intensity? What is the unit of measure? It is one of the important parameters that customers care about when choosing lights. However, not everyone clearly understands the concept, calculation, and characteristics of this parameter. For more information, refer to the article “What Is Lux?” below to get the most important details.
What is Lux?
The illuminance E (in lux) is a measure of the light flux per unit area. A sphere of 1m2 with a light source of intensity 1 candela will have an illuminance of 1 lux.
Lux (lx) is the SI unit for illuminance, it is the total illuminance over a surface area as described photometrically. Lux means luminous flux or luminous intensity Lumen per square meter (lm/m2) and is commonly referred to as illuminance.
Lux is an important unit of measurement in lighting devices. Lux and lumens both refer to the lighting ability of the bulb, but Lux has a difference that you need to keep in mind when choosing to buy the right bulb for your space.
What is the formula for calculating Lux?
According to regulations, illuminance is calculated by the formula: E = Φ/S (Lux: unit of illuminance)
More specifically illuminance = (Lamp power (w) x luminous flux (lm/w) x number of lights used)/ Lighting area (m2).
Or Lumen/m2 = Lux.
In which the number of bulbs needed for the space = (Illumination area (m2) x standard illuminance of the bulb)/ (lamp power x luminous flux)
Note that the luminous flux is the luminous efficiency per 1W of the light bulb in use according to the manufacturer’s announcement.
Reflectance coefficients for ceiling, wall, and floor are as follows: 50%, 80%, 20% respectively.
Looking at the Lux calculation formula above, it can be seen that the lamp with the higher luminous flux, the same power, the better the lighting ability. From there, the number of bulbs that need to be used is less, helping you save installation costs as well as reduce power consumption.
***Refer to more: What Are Lumens? Choose Energy-Efficient Bulbs with Lumens
The difference between Lux and Lumen
Lux and Lumen are quite confusing as both are measures of the light of a bulb, but lux has to consider the area of space while lumens do not.
If you buy an 800-lumen bulb and install it in a room with an area of 10m2, the lamp will have an illuminance = 80 Lux. However, also using the same lumen bulb on a larger room with a surface area of 20m2, the illuminance will be reduced to 40 Lux.
So it can be seen that, with the larger the room that needs lighting, you should choose the bulb with the higher illuminance. This is an important note that is very useful when choosing the right and highly effective lighting equipment.
How much Lux illuminance should you choose?
For large rooms, you should prioritize choosing high illuminance, but not all rooms need the same brightness but need to be based on specific lighting purposes.
For example, rooms that are mainly used for storage such as warehouses, basements, etc. will need relatively low light levels; while conference rooms, showrooms, work environments will require good quality of light so much higher brightness levels will be required.
Here are a few suggestions listed with Lux illuminance corresponding to specific cases to help you choose easily:
- 100 Lux – This light level is suitable for lighting in elevators, corridors, and stairs. Warehouse and storage areas will most likely also require this minimum level of light.
- 150 Lux – Restrooms and technical engine rooms require this level of light. This illuminance is suitable for simple activities. Simply illuminate the area.
- 200 Lux – Suitable for entrance and corridor areas.
- 300 Lux – Assembly area, detailed engineering needs at least 300 Lux illuminance.
- 500 Lux – General office space. This illuminance will be suitable for work on computers, machines, reading, studying…
- Above 500 Lux – If you need to light an area with complex work, then it is required to choose a bulb with a very high Lux value.
- Especially for spaces that require detailed and meticulous work, you can choose illuminance up to 2,000 Lux. For most general lighting purposes an illuminance of 500 lux will suffice.
***Refer to more: Top 7 Best Sunlight Desk Lamps Good For Your Work 
Standard illuminance of natural lighting
Natural light when shining on the ground has a constant value. It depends on the time of day and the state of the clouds and the reflectivity of the ground cover objects. Therefore, as researchers by scientists, chandeliers, wall lamps, floor lamps, and table lamps lighting must also comply with natural lighting standards to provide the amount of light that ensures safety for human health.
Standard luminance measurement units are being applied in civil and office lighting, factory lighting, and public lighting. The following are the standards for natural lighting illuminance:
- Sunlight during the day usually has an average illuminance that ranges from 32,000 lx to 100,000 lx.
- In good weather conditions and at dusk or dawn, the outdoor light also has an illuminance of about 400lx.
- The light reflected from the moon will usually have an illuminance of about 1 lx.
- The light from stars has an illuminance of about 0.00005 lx
- Television studios are usually illuminated with an illuminance of 1,000 lx.
- A bright office usually has an illuminance of about 400 lx.
***Refer to more: Best Daylight Lamp for Office: Top 8 Expert’s Choices of 2022
The link between Lux and how to choose quality lights
Light is an indispensable part of all human needs for living, production, and learning. Even during the day, lights are still required. This is extremely important for some important professions and fields such as graphic design, drawing, construction design, and laboratory work. Because if there is not enough brightness, it is easy to make mistakes in working, even cause occupational accidents.
Lux is an index showing the illuminance of a lighting device that has been carefully measured and calculated. Staying at this index will help provide the best brightness. Our eyes are less likely to get tired when too bright or have to strain too much because there is not enough light. Moreover, it also helps to partly limit the power consumption when lighting many wasted bulbs at the same time.
***Refer to more: Best Desk Lamps For Your Eyes: Top 10 Expert Picks
Can Watt be used to determine the brightness of a lamp?
The answer is no.
Watt represents the amount of energy the product consumes, not how much light (Lumen) the lamp provides. That is why you should not rely on the amount of Watt consumed, to choose to buy any lamp. It will only tell you how much energy the lamp uses, not how much light the lamp produces.
What is Lux of the LED?
This is a standard LED must ensure in lighting.
The luminous flux of an LED is measured in lumens. The higher the luminous flux an LED has, the stronger the light it emits and vice versa.
The CRI color rendering index reflects the fidelity of light colors, ranging from 0 to 100 Ra. With LEDs, this index is very high from 85-90 Ra.
The light efficiency of an LED is an indicator of the illuminance quality of the lamp. The unit is lm/w. The higher this index, the more energy-efficient the lamp is. Different spaces require different performances. Note: Do not choose bulbs with an efficiency below 70lm/w.
The color temperature range is wide, depending on the needs of the user, the customer can request the light color from the supplier.
The light distribution depends on the beam angle. The smaller the projection angle, the more concentrated the light will be compared to the larger projection angle. For office or factory areas, a projection angle of 120 – 150 is the most suitable.
The Lux is suitable for the office
Lighting design in the working room must ensure the factors of improving working efficiency and saving maximum power.
Therefore, when installing office lights, they must meet certain requirements for light intensity on the surface of each person’s desk.
The standard light for reading is 300 – 500 lux.
In a shared office, it must reach 400 lux; The staff rest room reaches 150 lux.
***Refer to more: Best Natural Light Desk Lamp: Top 8 Best Choices For Office
Hopefully, the useful knowledge in the article about What is Lux? can help you choose a lamp with a Lux degree that is suitable for your lighting space. Visit our website to update the latest information on the field of lighting bulbs.