Before we can begin any discussion about lighting there are several terms that are commonly defined in the industry to allow a shared vocabulary when looking at catalogs and deciding why one source might be relevant to an application.

Technical terms:

• Kelvin (also MacAdam Ellipses and how color can vary within the “same” color temperature)
• Color Rendering Index (8 color versus 15 color)
• Efficacy (lumens per watt)
• Hours (rated average life is when 50% of the lamps will fail or, for Solid State, 70% of lumen output)

Sun

• Color temperature: 5000 (direct) through 6500K (reflected sky)
• CRI: 100
• Efficacy: Infinity
• Lifetime: 10 billion years
• Technology: Miasma of incandescent plasma
• Pros: Low cost, easily available
• Cons: No control whatsoever, one day will go nova and destroy solar system

Fire

• Color temperature: 2400K
• CRI: 100
• Efficacy: Infinity
• Lifetime: Depends on log size
• Technology: Fuel with a high enough temperature
• Pros: Low cost, easily available
• Cons: Some control, difficult to keep alive when not needed

Incandescent

• Color temperature: 2800K
• CRI: 100
• Efficacy: 15-20 lumens/watt
• Lifetime: 750-1000 hours
• Technology: A thin coiled wire in a vacuum with glass envelope has electrical current run through it and it glows
• Pros: Fully dimmable, instant-on, high CRI, traditional source
• Cons: Low energy efficiency

Halogen

• Color temperature: 3000K
• CRI: 100
• Efficacy: 20-30 l/w
• Lifetime: 1000-2000 hours
• Technology: A thin coiled wire in a mixture of halogen gasses with glass envelope has electrical current run through it and it glows
• Pros: Fully dimmable, instant-on, high CRI, traditional source
• Cons: Low energy efficiency but better than incandescent

Fluorescent

• Color temperature: 3000K, 3500K, 4100K, 5000K, 6500K
• CRI: 70-90
• Efficacy: 80-100 l/w
• Lifetime: 25,000 hours
• Technology: An electrode at each end of the tube excites mercury atoms which releases ultraviolet photons which hit phosphors on the inside of the tube and are converted to visible light
• Pros: Dimmable with the right technology, the most energy efficient source
• Cons: Not always instant, CRI and light quality reduced when dimmed

Induction

• Color temperature: 3000K, 4000K, 5000K
• CRI: 70-90
• Efficacy: 60-90 l/w
• Lifetime: 100,000 hours
• Technology: Electromagnetic fields generated outside the lamp excite the mercury atoms which releases ultraviolet photons which hit phosphors on the inside of the tube and are converted to visible light
• Pros: Very long life, very efficient, no electrodes to fail
• Cons: High cost, lamp sizes are not standard, remote EM generator typically required

Fiber optics

• Technology: Not actually a source, uses metal halide or incandescent as a source and directs the light along a jacketed glass or plastic fiber to the destination
• Pros: Low temperature at illuminated end due to source being located elsewhere
• Cons: Source in remote box has a fan, fiber optic cabling can be problematic during installation

Neon

• Color temperature: Various colors and K depending on glass and gas mixture
• CRI: Varies, but can be similar to fluorescent
• Efficacy: Varies depending on length and dimming, from 10-25 l/w
• Lifetime: 25,000 hours
• Technology: An electrode at each end of the tube excites noble gas atoms which release visible light, the glass tube itself or phosphors inside the tube can work with the gas or added mercury to change the original gas color
• Pros: Can be bent nearly any shape, any length, any color
• Cons: Very high maintenance and replacement costs, high voltage transformer must be kept from public

Cold Cathode

• Color temperature: Various colors and K depending on glass and gas mixture
• CRI: Varies, but can be similar to fluorescent
• Efficacy: Varies depending on length and dimming, from 20-100 l/w
• Lifetime: 30,000 to 50,000 hours
• Technology: Very similar to neon but the cathodes do not heat up as much in order to excite the gasses, resulting in longer life
• Pros: Can be bent nearly any shape, any length, any color
• Cons: Very high maintenance and replacement costs, high voltage transformer must be kept from public

Sodium Vapor

• Color temperature: 2100-2700K
• CRI: 21-60
• Efficacy: 70-95 l/w
• Lifetime: 10,000-30,000 hours
• Technology: Electrodes strike an arc inside the lamp envelope with argon then vaporizing a chunk of sodium which brightens the arc as it turns into a gas
• Pros: Long life, high efficiency, inexpensive source
• Cons: Poor color rendering, poor color temperature, long startup time

Ceramic Metal Halide

• Color temperature: 3500K, 4100K
• CRI: 70-90
• Efficacy: 70-95 l/w
• Lifetime: 10,000-20,000 hours
• Technology: Electrodes strike an arc inside the lamp envelope with argon then vaporizing a mixture of metal halide salts which brightens the arc as they turns into a gas
• Pros: Long life, high efficiency, good color rendering, good color temperature
• Cons: Long startup time, expensive lamp costs

Plasma

• Color temperature: 6000K
• CRI: 90+
• Efficacy: 90-120 l/w
• Lifetime: 40,000 hours
• Technology: Radio-frequency signal from a power amplifier is guided into an electric field which then vaporizes the contents of the bulb to a plasma state at the bulb's center
• Pros: Small source, very efficient, good color rendering
• Cons: Still being developed, expensive, large size of amplifier, limited use outside entertainment at this time

LED

• Color temperature: Varies and many color options, higher CT have greater efficiencies
• CRI: Varies, 70-90
• Efficacy: 25-60 l/w
• Lifetime: 50,000 hours
• Technology: Charge-carriers flow across a diode from electrodes, electrons dropping down an energy level release energy in the form of visible light
• Pros: Long life, array of saturate rich colors, efficiency is improving
• Cons: Expensive, technology is not quite there yet, lots of misinformation