A complete Rochon lighting survey includes the following:
Illuminance is the amount of light falling on a surface. The unit of measurement is lux (or lumens per square metre = 10.76 foot candles, fc). A light meter is used to measure it. Readings are taken from several angles and positions.
Luminance is the amount of light reflected from a surface. The unit of measurement is candela per square metre (equals 0.29 foot-lamberts). An illuminance meter is used to measure it. Several measurements are made and averaged. Luminance tables are consulted for reference values.
Contrast is the relationship between the brightness of an object and its background. A luminance meter is used to measure it. The following formula is used to calculate contrast and provides a number between 0 and 1. The average contrast should be above 0.5:
Contrast= Luminance object – Luminance background
Reflectance is the ratio of light falling on a surface to the light reflected from a surface, expressed as a percentage. A light meter is used to measure it. Reflectance can also be measured using a reflectometer or by comparing the surface of interest with colour chips of known reflectance. To determine reflectance, the light meter probe is placed on the test surface to measure light falling on the surface. Next, place the probe 5-7 cm away facing the surface to measure the light reflected from the surface.
Rochon Engineering also performs Lighting Studies for Roadways
The Standard Practice for Roadway Lighting notes that the purpose of roadway lighting is to produce quick, accurate, and comfortable visibility at night; qualities which will safeguard, facilitate, and encourage vehicular and pedestrian traffic. The design criterion for lighting systems include: illuminance, luminance, and Small Target Visibility (STV). Illuminance based design calculates the amount of light incident on a roadway surface, whereas luminance based design calculates the amount of light directed toward the driver, predicting the luminance of the roadway. STV is used to determine the visibility of an array of objects on the roadway, and includes the calculation of target and background luminance, adaptation level, and disability glare.
