Candela
Definition and Overview
Candelas (cd) are a unit of measurement for light intensity, derived from the candela-second (csc), which was defined as one lumen per second. It is commonly used to express the brightness of light sources, including incandescent bulbs, fluorescent lights, and lasers.
History
The term “candelas” originated in the 17th century, when scientists began to study the properties of light. The British scientist James Bradley was the first to measure the luminosity of the Sun in 1667, but it wasn’t until the late 19th century that the concept of candela was developed.
Physics
A candela is defined as one lumen per second, or 1⁄3600 of a lux. It represents the amount of visible light emitted by an object or source. The candela-second (csc) is equivalent to the luminous flux density of a given source, and it is used to express the brightness of various sources.
Units
There are several units that are used to measure light intensity, including:
- Candelas (cd): 1⁄3600 lux
- Lumens (lm): 1 lumen = 1⁄60 candela-second
- Lux (lx): 1 lux = 1 candelas per square meter
Applications
Candelas are widely used in various fields, including:
- Lighting: Candelas are used to measure the brightness of incandescent bulbs and other lighting sources.
- Optics: Candelas are used as a standard unit of measurement for optical instruments, such as spectrometers and interferometers.
- Astronomy: Candelas are used to measure the brightness of stars and other celestial objects.
Examples
Incandescent Bulbs
Incandescent bulbs emit light through heating a thin wire filament. The candela-second (csc) is commonly used to express the brightness of incandescent bulbs, with higher values indicating brighter lights.
| Bulb Type | Candela-Second (cd) |
|---|---|
| Incandescent | 100-500 cd |
| Halogen | 500-1500 cd |
Fluorescent Lights
Fluorescent lights emit light through exciting gas atoms, which then release energy in the form of photons. Candelas are used to measure the brightness of fluorescent lights.
| Light Type | Candela-Second (cd) |
|---|---|
| T8 Fluorescent | 200-400 cd |
| LED Fluorescent | 100-300 cd |
Lasers
Lasers emit light through stimulated emission, where energy is released in the form of photons. Candelas are used to measure the brightness of lasers.
| Light Type | Candela-Second (cd) |
|---|---|
| Nd:YAG Laser | 20-100 cd |
| Diode-Pumped YAG Laser | 10-50 cd |
Measurement Techniques
Candelas can be measured using various techniques, including:
- Spectrophotometry: This involves measuring the absorption and emission spectra of a light source to determine its luminous intensity.
- Photometry: This involves measuring the brightness of an object or light source directly using a photometer.
Safety Precautions
Working with candelas requires careful attention to safety precautions, including:
- Using gloves and protective eyewear when handling incandescent bulbs
- Ensuring proper ventilation when working with fluorescent lights or lasers
- Following proper procedures for measuring candela-second values to avoid errors.