There is no direct conversion factor between lux and watts because lux is a measure of illuminance (light falling on a surface), while watts are a measure of power. The relationship between them depends on the specific light source and the area over which the light is distributed.
Here's a breakdown of why this is the case:
- Lux (lx): Measures the amount of light falling on a surface. Specifically, it is lumens per square meter (lm/m²).
- Watts (W): Measures the power consumed by a light source. This is a measure of energy used, not light emitted.
- Lumens (lm): Measures the total amount of visible light emitted by a light source.
The efficiency of a light source in converting watts into lumens is what bridges the gap, but this efficiency varies greatly depending on the type of lamp.
Why a Direct Conversion is Impossible:
The number of lux you get from a certain wattage depends on:
- The type of light source: Incandescent, fluorescent, LED, and other types of lights have drastically different efficiencies (lumens per watt). LEDs are much more efficient than incandescent bulbs.
- The distribution of light: A focused beam of light will produce higher lux values in the focused area than a diffuse light source with the same lumen output.
- Distance from the light source: Illuminance (lux) decreases with distance from the light source.
- Reflectivity and Absorption: The properties of the surfaces onto which the light falls impact how much light is reflected or absorbed, influencing illuminance.
Example:
A 100-watt incandescent bulb might produce around 1600 lumens. If all that light were focused on a 1 square meter area, you'd have 1600 lux. However, a 20-watt LED bulb can produce roughly the same amount of lumens (1600 lm). Therefore, 20 watts could also give you 1600 lux over 1 square meter. The wattage to lux conversion is drastically different in each case.
How to Determine Lux from a Light Source:
- Find the lumen output of the light source: This is usually printed on the bulb or fixture packaging.
- Determine the area the light is illuminating: Measure the surface area in square meters.
- Estimate Lux: Divide the lumens by the area in square meters to get an approximate lux value. Lux = Lumens / Area (m²)
In summary, you can't directly convert watts to lux without knowing the lumen output and the illuminated area.
