The most common method for measuring LED light intensity (usually referred to as illuminance, i.e. the brightness of the illuminated surface) is to use a lux meter. Here are the detailed steps and precautions:
1. Core tool: Lux meter
Principle:
The lux meter measures the luminous flux received per unit area (unit: Lux = lumen/square meter lm/m²), which is consistent with the sensitivity of the human eye to visible light.
Applicable scenarios:
Daily applications such as indoor lighting, desk lamp brightness, display backlight, etc.
2. Measurement steps
Prepare the environment:
Turn off other light sources to avoid interference.
Let the LED lamp preheat for 10-15 minutes (light output varies with temperature).
Set up the lux meter:
Select the range (such as 0~50,000 Lux).
Confirm that the instrument supports LED spectrum correction (check whether the manual is marked with "f₁'<5%" or "Class L").
Place the sensor:
Align the sensor head of the illuminance meter vertically to the LED light source and place it at the location to be measured (such as a desktop or wall).
The distance between the sensor head and the LED needs to be fixed (the greater the distance, the lower the illuminance).
Read the data:
Keep it stable for 3~5 seconds and record the stable value.
Take the average value of multiple measurements (reduce errors).
III. Key points
Distance effect:
LEDs have strong directionality. When the distance is doubled, the illuminance drops to 1/4 (inverse square law).
Example: 1000 Lux measured at a distance of 10 cm → about 250 Lux at 20 cm.
Angle calibration:
The sensor head needs to be perpendicular to the light (tilts will cause errors).
Professional illuminance meters need to support cosine correction (to cope with oblique incident light).
Spectral matching:
Cheap illuminance meters may underestimate blue light/cold white LEDs (the human eye is less sensitive to blue light).
Solution: Choose an instrument marked with "Class L" or "CIE spectral response".
3. Advanced measurement methods
Measurement target Tools Applicable scenarios
Total luminous flux (lumens) Integrating sphere + spectrometer LED bulb/tube factory test
Beam angle intensity (candela) Distributed photometer Directional lighting design such as car lights and spotlights
Spectral power distribution Spectral radiometer Plant growth lamps, medical light source research and development
💡 Ordinary users do not need these devices unless they are engaged in optical engineering.
4. Alternative solutions (simple method)
Mobile APP illuminance meter (such as "Lux Light Meter"):
Advantages: free and convenient.
Disadvantages: low accuracy (error more than ±20%), for reference only.
Comparison method:
Use LED lights with known parameters (such as 500 lm marked on the package) to irradiate at the same distance and compare the brightness difference.
5. Common misunderstandings
❌ Use "wattage (W)" to measure brightness: wattage only represents power consumption, and the brightness of LEDs with the same wattage may differ by 2 times!
❌ Ignore LED temperature: The longer the LED works, the lower the brightness (light decay), and the cold state measurement is inaccurate.
📌 Tip: Calibrate the instrument before measurement (use standard light source or send it to a professional institution)!
If you need to measure the total luminous output (lumens) or spectrum of the LED, it is recommended to send it to a professional laboratory (the cost is about ￥300~1000/time). The lux meter is completely sufficient for daily use! for more lux intensity , please visit http://www.benweilight.com
