Flashlight Terms

Beam Types

See Nitecore: The Anatomy of a Flashlight Beam for details

• Floody - a wider beam intended to illuminate a large area
• Spotty / Thrower - a light which throws a tight beam a long distance with a small spot at the end
• Blended Beam - A beam composed of both floody and spotty features. 

Reflector Types

• Smooth - typically used for throwers to direct the beam down range in a tighter spot
• Orange Peel - typically used in floody lights. The texture causes the light to spread out at various angles from the head of the light.

Lens Types

The lens will either be a flat piece of glass which relies on the reflector the change the profile of the beam. An aspherical, typically flat on one side and convex on the other. Or a TIR lens.

• TIR - Total Internal Reflection - A TIR lens is an optical lens built on the principal of  (TIR). TIR lenses are often cone-shaped and rotationally symmetrical, with a refractive lens inside a reflector. When a LED light is covered with a TIR lens, the lens captures the light photons and directs them in a desired direction.
• Typically they vary from:
• 10 degrees for spotty beams
• to 60 degrees for floody beams
• SEE ESKMA OPTICS for detailed descriptions of the following
• Aspherical - is simply a lens which is not a perfect sphere typically described with the following terms.
• Convex -  indicating the curve forms a bubble curving outwards with a uniform curvature
• Concave - indicating the curve forms a cup curving inwards with uniform curvature
• Plano - indicating flat on one side 
• Plano Concave - indicating flat on one side and concave on the other
• Plano Convex - indicating flat on one side and convex on the other. Used to focus a beam to a specific focal length. Zoomies use these lenses to focus a beam  into either a tight or wide beam depending on how far away from the LED light source they are positioned. 
• If the lens is closer to the LED it will create a wide beam.
  
• If further away than it will focus the beam at a specific focal point where start forming a wider beam beyond the focal point
• Focal Point - point at which a convex lens will focus light to a point. This is where the maximum light of the LED will be focused to a small point and can set easily flammable objects such as paper on fire. Most flashlights set the focal points so this cannot be achieved for safety purposes.

CRI - Color Rendering Index (CRI) is a measurement of how natural colors render under an artificial white light source when compared with sunlight. The index is measured from 0-100, with a perfect 100 indicating that colors of objects under the light source appear the same as they would under natural sunlight.

Kelvin - refers to the unit used to measure the color temperature of LED lights, where a lower Kelvin value indicates a warmer color (like yellow) and a higher Kelvin value indicates a cooler color (like blue). Essentially, the Kelvin scale determines how "warm" or "cool" the light appears to the human eye.
See Led Light Experts for details on Kelvin scale 

Dedomed - Dedoming is the process of removing a dome on an led. The dome is the silicone hemisphere on top of some LED's. The purpose is to create more internal reflections and thus, more lumens. Domes also give a floody beam profile, lowering candela.

See Reddit Thread

Zoomies - variable focus head. This moves a plano covex lens varying the focal point so the beam forms either a wide beam or a tight spot at the end.

• Slidy Zoomies - these types of zoomies use a simple slide action to adjust the focus of the beam. These are NOT INTENDED as weapon lights as the recoil from the weapon will most likely change the position of the lens. These also compromise the water resistance of the light potentially exposing the emitter to humidity or water.
• Twisty Zoomies - these types of zoomies are typically intended for use on a weapon light. They will usually not be affected by the recoil of the weapon. They also maintain water resistance much better than the slidy zoomies.

LEP - Laser Excited Phosphor - these types of flashlights are extremely bright in the center of the beam and without any real spill typically throwing a beam a great distance depending on the lumens generated by the LED.

Heat Sinks

See DNP Products and Services: What are Heat Sinks?

Passive Heat Sink -  many higher powered flashlights will have heat sink fins to dissipate the head generated from the LED. These appear as concentric rings of metal just behind the Lens and LED. General rule is the number and size of the fins will create a greater cooling effect.

• On the Lumitop GT4695 they look like this:

Active Heat Sink - a heat sink with fans which circulate air across the heat sink fins to create a greater cooling effect than the passive heat sink fins.

• On the Lumintop Mach 4695 they pull air in from the front vent:
  
• Then push the cool air out over the heat sink fins:
  
• This configuration dissipates the heat across the fins allowing for longer runtimes at higher lumens.

LED Domed or De-domed - In general a de-domed LED will give you better throw.  While a domed LED will give you more flood.

Candela vs Lumen

See Video: How Lumens Lux and Candela Relates to Throw and Flood in Flashlights.

In general with larger number....

• Candela will represent how good a thrower the flashlight is
• Lumens will represent how good a floody it will be

Credits:

Brian Richards for his posts on general flashlight terminology

ESKMA OPTICS for detailed descriptions of the different types of lenses
Advanced Optics OPTICAL LENSES AND CONVEX/CONCAVE MIRROR THEORY

Reddit Thread for discussion of doming leds

1000 Bulbs for candela, lumen and flux definitions

Led Light Experts for explanation of the Kelvin 

Lumintop for the GT4695 and the Mach 4695

DNP Products and Services: What are Heat Sinks?

Nitecore "The Anatomy of a Flashlight Beam" for general beam discussion