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한국어 Watts, lumens, candela and lux are three such terms that are essential when considering modern lighting solutions, especially with the rise of LED technology. Understanding lighting can be a complex endeavor due to the various terms and metrics used to describe different aspects of light. This article will delve into the definitions of these terms, explaining what they mean, how they relate to each other, and how to convert between them.
What is a Watt in a Lighting Fixture?
Watts measure the amount of electrical power consumed by a light source. The higher the wattage, the higher the power consumption.
Historically, higher wattage was associated with brighter light, especially in incandescent bulbs. However, with advancements in LEDs, watts no longer directly indicate brightness. For instance, a 10-watt LED bulb can produce the same amount of light as a 60-watt incandescent bulb.
- Electricity consumption per hour (kWh) = Power (W) × 0.001
Lumen Definition
Lumen (abbreviated lm) is the unit of luminous flux. Lumens measure the total amount of visible light emitted by a light source. The higher the lumen number, the more visible light the lights releases, and brighter it appears. Lumens and watts are often converted to each other based on luminous efficacy (lm/W).
- Lumens represent the total amount of light emitted by a lamp, regardless of direction.
Lux Definition
Lux is a measure of illuminance, representing how much light reaches a specific area. One lux equals one lumen per square meter. While lumens tell you how much light a source emits, lux indicates how much of that light actually reaches and illuminates a surface.
The higher the Lux, the brighter the surface is under light. For lights with same power and lumens, the higher the installation height, the lower the surface illumination(lux) will be.
- Garage lighting: 100 lux is sufficient, which means 100 lumens of light per square meter.
- Factory or warehouse: 500 lux is required, which means 500 lm of light per square meter.
Candela Meaning
Candela (symbol cd) is a unit of light intensity, used to express the amount of light emitted by a light source in a specific direction. The more concentrated the light is in one direction, the larger the candela value; the more dispersed the light is, the smaller the candela value is.
For example, a light is shining directly forward, the light is most concentrated in the direction directly in front of the light, so the candela is the highest, while the candela will be lower in the direction to side.
- Flashlight: Light intensity is higher in the front, and can illuminate farther.
- Desk lamp: Light is dispersed, with low candela in all directions.
Candela vs Lumens
Candela(cd) and lumen(lm) are both fundamental units of physics in optics, but their core definitions are completely different.
- Lumen describes the total amount of visible light emitted by a light source in all directions.
- Candela describes the luminous intensity of a light source in a specific direction.
| Light Source Type | Candela (cd) Meaning | Lumen (lm) Meaning |
|---|---|---|
| Laser Pointer | Key (light is highly concentrated, cd value very high) | Secondary (total light output may be very small) |
| Car Headlight | Important (determines beam distance and central brightness) | Important (total luminous flux affects illumination coverage) |
| Indoor Light Bulb | Not often used | Core (determines overall room brightness) |
Note: Candela to Lumen conversion is not possible. You need to know the light source’s beam angle (solid angle). For example:
- A 100-cd light source with a narrow beam (10°) will produce less total lumens.
- A 100-cd light source with a wide angle (120°) will produce more total lumens.
Convert Lumens to Watts
Converting watts to lumens varies greatly, depending on the luminous efficacy (lm/W) of the light. Different types of light sources (incandescent, halogen, fluorescent, LED) and different brands and models of the same light source have different luminous efficacy.
So you only need to know the luminous efficacy (lm/W) of the light to convert between lumens and watts.
- Lumens to watts calculator ：Watts = Lumens ÷ Luminous Efficacy (lm/W)
- Watts to lumens calculator ：Lumens = Watts × Luminous Efficacy (lm/W)
Lumens to watts conversion chart Example: Luminous efficiency is 100lm/W
| Lumens (lm) | Lumens to Watts | Watts (W) |
|---|---|---|
| 800lm | Lumens(lm) ÷ 100 lm/W | 8W |
| 1000lm | 10W | |
| 1500lm | 15W | |
| 5000lm | 50W | |
| 10000lm | 100W |
This conversion chart is just an example. You can calculate it based on the actual light efficiency of your light.
Convert Lux to Lumens
Lumen indicates the total amount of visible light emitted, and lux indicates how many lumens of light are received by one square meter of surface.
Therefore, when converting lux to lumens, you must know the area of the illuminated surface! Lux is an area-related density unit and cannot be converted to lumens without considering the area.
Convert lux to lumens or lumens to lux calculator:
- Lumen (lm) = Lux (lx) × Area (㎡)
- Lux (lx) = Lumen (lm) ÷ Area (㎡)
Convert lux to lumens steps:
- Use a lux meter to measure the illuminance (lx) of the illuminated surface (tabletop, floor). For example, 500 lux.
- Measure the length and width of the area and calculate the area: Area = Length (m) × Width (m).For example, 2 ㎡.
- Calculate lumens: 1000 (lm) = 500(lux) × 2(㎡).
| Target | Area | Convert | Description |
|---|---|---|---|
| Desk surface illumination reaches 500 lux | 0.72 ㎡ | 500 lux × 0.72 ㎡ = 360 lm | Lights with a luminous flux ≥ 360 lm are required. |
| Check whether the room lights are bright enough Luminaire 1000lm | 12 ㎡ | 1000 lm ÷ 12 ㎡ ≈ 83 lx | Lower than the recommended illumination of the room additional light sources are needed! |
Lumen vs Candela vs Lux
| Concept | Definition | Unit | Key Feature | Example |
|---|---|---|---|---|
| Luminous Flux | Total amount of light emitted by a source | Lumen (lm) | Emphasizes “total amount”, regardless of direction | A light bulb emitting all its light |
| Luminous Intensity | Light strength in a specific direction | Candela (cd) | Emphasizes “directionality”, how concentrated the light is | Flashlight beam |
| Illuminance | Degree to which a surface is lit | Lux (lx) | Emphasizes “illuminated object”, light per unit area | Brightness on a desk |
Summarize
In conclusion, understanding the relationship between lux, lumens, watts, and other lighting terms is critical to making decisions about industrial and commercial lighting solutions. When faced with different locations or lighting needs, these units will differ in the type and installation of lights.
People Also Ask
How many lumens is a 100 watt bulb?
There is no fixed conversion relationship between watts and lumens; the luminous efficacy (lm/W) must be determined.
- 100W incandescent (12–16 lm/W): 1200–1600 lm
- 100W CFL (50–60 lm/W): 5000–6000 lm
- 100W LED (80–100 lm/W): 8000–10000 lm
Does the greater the wattage, the greater the lumen value?
Strictly speaking, higher wattage doesn’t necessarily mean higher lumens. The relationship between the two depends on the luminous efficacy (lm/W) of the light source.
- Different lamp types:
100W incandescent lamp → 1500 lm; 20W LED → 1800 lm - Same lamp type:
100W LED (80 lm/W) → 8000 lm; 80W LED (130 lm/W) → 10400 lm
Does the greater the lumen value, the greater the lux?
Not necessarily. If the lumens emitted by a light source increase, but the light distribution area also increases, the lux value may remain the same or even decrease.
For example, different beam angles and different mounting heights of the same light will affect the light coverage area.
Which factor determines the value of candela?
The value of candela (cd) is usually determined by the luminous flux and the luminous angle. The greater the lumens and the smaller the beam angle, the larger the candela will be.
Is the maximum lux the better?
Of course not. Different scenes have recommended lux ranges. Too high or too low will affect the lighting experience.
Too high can cause glare, dazzling, fatigue, and even pose safety risks. If it is an operating room or a factory, higher lux can ensure efficiency and safety.
