A photometer with a detector filtered to match the V-lambda curve and a diffuser shaped for cosine response, so light arriving at angles counts correctly. Field measurements are taken on a grid at work plane height, typically 0.75 m or 30 inches, or vertically for faces and walls. Cheap meters with poor spectral matching can misread narrow-band LEDs by 10 percent or more, which matters for commissioning disputes.
Grab the illuminance meter and shoot the grid at desk height, the owner says the east bay is darker than the calc.
Also heard as
- light meter
- lux meter
- foot-candle meter
Related terms
Illuminance
The amount of light falling on a surface per unit area, measured in lux or foot-candles.
V-lambda curve
The standard curve of the eye's daytime sensitivity to each wavelength, peaking in green at 555 nm.
Spectroradiometer
An instrument that measures light's power at each wavelength, from which color and photometric values are calculated.
Point-by-point
A lighting calculation that predicts illuminance at each point on a grid from every luminaire's photometric data.