--- title: "Illuminance / Light Sensors & Monitoring | Aethair" description: "Illuminance is the visible light falling on a surface, measured in lux (one lumen per square meter). See how it is measured and the monitor that tracks it." url: https://aethair.io/parameters/light/ --- Measurements · Radiation & Light # Illuminance / Light Also known as illuminance, light level, ambient light Illuminance / light level. [Schedule a call](https://calendly.com/d/ctdd-mkr-v9v/aethair-demo-website) [Configure Illuminance / Light Monitoring](https://aethair.io/build/?params=light) At a glance lux Radiation & Light 1 way to measure it - **Aethair PRO** Built-in sensor What it is ## What is illuminance (light)? Illuminance is the amount of visible light falling on a surface, measured in **lux** (one lux is one lumen per square meter). It is a photometric quantity, meaning it is weighted to the sensitivity of the human eye across the spectrum, so it reflects how bright a surface appears to a person rather than the raw radiant energy present. This distinguishes it from solar radiation, which measures the total shortwave energy in W/m², and from luminance, which measures the light emitted or reflected toward the eye from a surface. Illuminance is what a lux meter reads on a desk, a floor, or a workbench, and it is the standard measure of how well a space is lit. Because it captures the light actually available for a task, illuminance is the working currency of lighting design, daylighting, and visual comfort. ### Health and operational effects Adequate light is a health and safety matter: too little causes eye strain, fatigue, and errors, and raises the risk of trips, falls, and accidents, while poorly balanced lighting produces glare and discomfort. Guidance sets recommended maintained illuminance levels for different tasks, from circulation areas to fine detailed work, and workplace assessments check that these are met. Beyond simple adequacy, the timing and intensity of light influence the circadian system, which is why daylight provision and light exposure feature in well-being standards such as WELL, and why daylight harvesting (dimming electric light as daylight rises) is a mainstay of energy-efficient buildings. For facilities and building operators, illuminance is therefore both a compliance and comfort measure and a lever for energy saving. How it is measured ## How Illuminance / Light Is Measured Illuminance is measured with a **photometric sensor**, a light detector filtered to match the eye's response and **cosine-corrected** so that light arriving at an angle is weighted correctly for a flat surface. The **Aethair family includes a built-in light sensor** that reports illuminance in lux continuously as part of the same unit that measures air quality, so ambient light becomes part of the indoor-environment picture. Where a task-specific or survey-grade measurement is needed, a dedicated lux meter or photometric probe can instead be logged on a Thiamis gateway. Sensors need periodic calibration, as optical filters and detectors drift over time. Built into Aethair PRO 1 Measured by the monitor's own sensors, calibrated before it ships: nothing to add. ### Placing light sensors Illuminance is measured at the plane that matters (usually the working plane, such as desk height for offices or the floor for circulation areas), with the sensor horizontal and facing up, or oriented to match the task where the work is not horizontal. The key is to avoid casting a shadow on the sensor or letting a single bright source dominate unrepresentatively, and to measure where people actually work. The built-in Aethair sensor reports the light where the unit is mounted, giving a good picture of ambient conditions in the occupied space. ### Every device and option that measures Illuminance / Light 1 | Device / option | Type | Base platform | Measures | | - | - | - | - | | **Aethair PRO built-in sensors** | Built-in sensors | Aethair PRO | Illuminance / Light [Dew Point](https://aethair.io/parameters/dew_point/) [Heat Index](https://aethair.io/parameters/heat_index/) [Relative Humidity](https://aethair.io/parameters/humidity/) [Particle Count (by size)](https://aethair.io/parameters/particle_count/) [PM1](https://aethair.io/parameters/pm1/) [PM10](https://aethair.io/parameters/pm10/) | [Configure Illuminance / Light Monitoring](https://aethair.io/build/?params=light) Article Library ## Reading on Illuminance / Light ### [How to Choose an Air Quality Monitor: PRO, IAQ, or Thiamis](https://aethair.io/resources/choosing-aethair-monitoring-device/) Compare Aethair PRO, IAQ, and Thiamis to match the right device to your site, from commercial interiors to industrial and fenceline monitoring. [All articles](https://aethair.io/resources/) Related ## More in Radiation & Light [Solar / Global Radiation](https://aethair.io/parameters/solar_radiation/) [PAR (Photosynthetically Active Radiation)](https://aethair.io/parameters/par/) [UV Index](https://aethair.io/parameters/uv/) [Radon](https://aethair.io/parameters/radon/) Questions ## Illuminance / Light FAQ What is the difference between lux and lumens? Lumens measure the total light output of a source, while lux measures how much of that light lands on a surface: one lux is one lumen per square meter. The same lamp gives a high lux close up and a low lux far away, so lumens describe the source and lux describe the illumination at a place. How is illuminance different from luminance? Illuminance is the light falling onto a surface, measured in lux, whereas luminance is the light traveling from a surface toward the eye, measured in candela per square meter. Illuminance tells you how well lit a task is; luminance relates to how bright a surface or display appears and to glare. How does light differ from solar radiation? Light (illuminance) is a photometric measure weighted to the human eye and reported in lux, while solar radiation is the total shortwave energy in W/m². They measure related but different things, so a bright day has both a high illuminance and a high irradiance, but neither converts directly into the other. How do I monitor light levels? The Aethair family reports illuminance from its built-in light sensor for continuous ambient monitoring, while a dedicated lux meter on a Thiamis gateway suits task-specific or survey measurements. Use the configurator to combine light with temperature, humidity, and the other indoor-environment parameters your space needs.