Introduction to the basics of photometrics

Introduction to the basics of photometrics

1, Definition??

①?Luminous intensity: the amount of luminous flux per unit stereo angle.

Symbol: I; Unit: candela (cd), derived in: lm / sr Light intensity is a distance-independent quantity, which is important.

②?Illuminance: The amount of luminous flux received per unit area. Symbol: E; unit: lux (Lux), derived unit: lm / m2 the illuminance value of a place, with the distance from the place to the light source, but also with the direction. Care must be taken in practical applications.??

③?Beam angle: the luminous intensity is equal to the angle between the two sides of the light intensity N% of the center of the beam.

The N value is specified as follows：

CIE-?International Commission on Illumination (Europe)

1/2 Imax

IES-?American Society of Lighting Engineering??

1/10 Imax

Due to the diversity of lighting fixtures, the luminous spots emitted from the lamps are very different, especially for some small angle spotlights. Therefore, it is sometimes not possible to distinguish and recognize the luminous distribution of a luminaire by giving only one N value. It is recommended that the luminaire manufacturer give beam angle data for both N values.??In addition, 1/2 Imax is often referred to as half-peak edge angle.??In fact, it is better to define 1/10 Imax as the beam angle and 1/2 Imax as the half-peak edge angle.

2,?Conversions between photometric quantities

Here we mainly introduce the conversion relationship between light intensity and illuminance, which is commonly used in lighting design.

(1) formula, r is the light source or luminaire out of the photometric center to the irradiated surface of the test point distance.??

Formula (1) is the basic formula for the light distribution curve test, but also to do the basic formula for lighting design.??

Need to note:

①?Formula (1) in the illuminance, is the light source or luminous surface of the lamp at the corresponding angle of the normal illuminance. Or, the normal direction of the illuminance meter probe must point to the light source or luminous surface of the luminous center. But in practice, the application of the formula (1) may require some variations, which will be introduced later.??

②?Formula (1) is only applicable to point light sources?

In the next issue I will introduce light distribution curves and their applications