Lighting Source
Fluorescent
Fluorescent tube is a low-pressure mercury-vapor gas-discharge lamp that uses fluorescence to produce visible light. The typical luminous efficacy of fluorescent lighting systems is 50–100 lumens per watt, several times the efficacy of incandescent bulbs with comparable light output.
Fluorescent lamp requires a ballast to regulate the current through the lamp, but contain mercury, many fluorescent lamps are classified as hazardous waste. Environmental Protection Agency recommends that fluorescent lamps be segregated from general waste for recycling or safe disposal, and some jurisdictions require recycling of them.
Light-emitting diode (LED)
A light-emitting diode (LED) is a semiconductor light source that emits light when current flows through it. Electrons in the semiconductor recombine with electron holes, releasing energy in the form of photons. The color of the light (corresponding to the energy of the photons) is determined by the energy required for electrons to cross the band gap of the semiconductor. White light is obtained by using multiple semiconductors or a layer of light-emitting phosphor on the semiconductor device.
luminous efficacy
Luminous efficacy is a measure of how well a light source produces visible light. It is the ratio of luminous flux to power, measured in lumens per watt in the International System of Units (SI).
| Light Source | Type | Overall luminous efficacy (lm/W) | Overall luminous efficiency |
|---|---|---|---|
| Incandescent | 5, 40, 100 W tungsten incandescent (120 V) | 5, 12.6, 17.5 | 0.7, 1.8, 2.6% |
| Light-emitting diode (LED) | Theoretical limit for a white LED with phosphorescence color mixing | 260-300 | 38.1–43.9% |
| Ideal sources | Truncated 5800 K black-body | 251 | 37% |
| Light-emitting diode | 21.5 W LED retrofit for T8 fluorescent tube (230 V) | 172 | 25% |
| Light-emitting diode | 11 W LED screw base lamp (230 V) | 138 | 20.3% |
| Gas discharge | 1400 W sulfur lamp | 100 | 15% |
| Gas discharge | Low-pressure sodium lamp | 100-200 | 15-29% |
| Gas discharge | High-pressure sodium lamp | 85-150 | 12-22% |
| Fluorescent | PL-S 11 W U-tube, excluding ballast loss | 82 | 12% |
| Fluorescent | T8 tube with electronic ballast | 80-100 | 12-15% |
| Fluorescent | 70–150 W inductively-coupled electrodeless lighting system | 71-84 | 10-12% |
| Fluorescent | T5 tube | 70-104.2 | 10-15.63% |
| Gas discharge | Metal halide lamp | 65-115 | 9.5-17% |
| Fluorescent | 32 W T12 tube with magnetic ballast | 60 | 9% |
| Arc lamp | Ultra-high-pressure (UHP) mercury-vapor arc lamp, free mounted | 58-78 | 8.5-11.4% |
| Arc lamp | Mercury-xenon arc lamp | 50-55 | 7.3-8% |
| Fluorescent | 9–32 W compact fluorescent (with ballast) | 46-75 | 8-11.45% |
| Halogen incandescent | Photographic and projection lamps | 35 | 5.1% |
| Arc lamp | Xenon arc lamp | 30-50 | 4.4-7.3% |
| Arc lamp | Ultra-high-pressure (UHP) mercury-vapor arc lamp, with reflector for projectors | 30-50 | 4.4-7.3% |
| Cathodoluminescence | Electron stimulated luminescence | 30 | 5% |
| Halogen incandescent | Tungsten quartz halogen (12–24 V) | 24 | 3.5% |
| Halogen incandescent | 2.6 W tungsten halogen (5.2 V) | 19.2 | 2.8% |
| Halogen incandescent | Halogen-IR (120 V) | 17.7-24.5 | 2.6–3.5% |
| Halogen incandescent | 100, 200, 500 W tungsten halogen (230 V) | 16.7, 17.6, 19.8 | 2.4, 2.6, 2.9% |
| Incandescent | 15, 40, 100 W tungsten incandescent (230 V) | 8.0, 10.4, 13.8 | 1.2, 1.5, 2.0% |
| Arc lamp | Carbon arc lamp | 2-7 | 0.29–1.0% |
| Gas discharge | Plasma display panel | 2-10 | 0.3–1.5% |
| Combustion | Gas mantle | 1-2 | 0.15–0.3% |
| Combustion | Candle | 0.3 | 0.04% |
| Light-emitting diode | LED screw base lamp (120 V) | Up to 102 | Up to 14.9% |
Color Rendering Index (CRI)
A color rendering index (CRI) is a quantitative measure of the ability of a light source to reveal the colors of various objects faithfully in comparison with an ideal or natural light source.
Color rendering: Effect of an illuminant on the color appearance of objects by conscious or subconscious comparison with their color appearance under a reference illuminant
The CRI of a light source does not indicate the apparent color of the light source; that information is given by the correlated color temperature (CCT). The CRI is determined by the light source’s spectrum.
Correlated color temperature (CCT)
The correlated color temperature (CCT, Tcp) is the temperature of the Planckian radiator whose perceived color most closely resembles that of a given stimulus at the same brightness and under specified viewing conditions