Li-ions, LEDs & Links

Flashlight Product Names

Our product name strings can be a little scary, but they break down into the following fields:
  • number and type of batteries
  • maximum brightness in lumen (lm)
  • number of modes or brightness levels
  • type of power-LED being used (see below)
  • manufacturer and product name and/or model
  • LED-bin (LEDs are sorted by brightness when manufactured)
For example, the
    1xAA 150lm 3-level XP-G2 'Fenix HL23' R5
flashlight uses one AA battery, produces a maximum of 150 lumen with 3 levels (high, medium, low) from a Cree® XP-G2 R5-bin LED. The manufacturer is Fenix and their model number is HL23. We put the LED-bin string (R5) at the end of the description because manufacturers often release different versions of the same model light using higher-bin LEDs (but not necessarily with higher output), so the LED-bin tag can differentiate between model versions.

Batteries

Common battery chemistries are Alkaline, Nickel Metal Hydride (NiMH), Lithium-metal and Lithium-ion (Li-ion). Of these, Alkaline and Lithium-metal cells are non-rechargeable, and NiMH and Lithium-ion cells can be recharged between 500 and 1000 times. Batteries have an energy density figure measured in Watt-hours (Wh) that depends on the chemistry and volume of the cell. You can use the Wh figure to compare expected run-times using different types of batteries when used in the same light.

On the far left is an 18650 (3.7 volt @ 2600mAh = 9.6Wh) Lithium-ion rechargeable battery, next to that an AA (1.2 volt @ 2000mAh = 2.4Wh) rechargeable NiMH, then a matchbox for size comparison. On the right is a CR123A (3 volt @ 1400mAh = 4.2Wh) non-rechargeable Lithium-metal "camera" battery, commonly used in the USA and Asia as a flashlight battery.

Note that the 18650 (nominal 18mm x 65.0mm) is around twice the length of the CR123A (16mm x 34mm), but slightly larger in diameter. A flashlight designed to use both has a larger diameter body and must cope with a wider voltage range (typically 2.7 volts through 10 volts or more). For the runtime comparison mentioned above, an 18650 cell at 9.6Wh would last longer than two CR123A cells at 4.2Wh each (total 8.4Wh).

18650 cells can be purchased with an inbuilt over-current, over & under-charge protection circuit. We strongly recommend that you only use Protected 18650 Li-ion cells in flashlights.

For more information on Li-ion batteries, see the Wikipedia Lithium-ion battery web page.
For more information on NiMH batteries, see the Wikipedia Nickel-metal hydride battery web page.

LEDs

LEDs are Light Emitting Diodes. An electric field applied to a semiconductor P-N junction produces energy in the form of photons. This is the process of electroluminescence. As well as low level output used for indicators, LEDs can be made in high-power versions designed for illumination. This form of LED produces quite a lot of heat, and one of the critical design parameters for LED flashlights is in dispersing this heat as efficiently as possible to avoid shortening the LED lifetime.

For much more information on LEDs, see the Wikipedia Light-emitting diode web page.

Power-LEDs

The following is a list of Power-LEDs that have historically been found in our flashlight range. You can see a steady improvement in their efficacy (output brightness in lumen per watt of power consumed). For more information, see the LED Manufacturer links below. The different LED images are at approximately the same scale. The yellow rectangle in the middle is the LED die, the light emitter.

Cree® XLamp® XR-E EZ1000
Viewing Angle: 90°
Chip size: 980um x 980um
LED size: 7mm x 9mm x 4.4mm
Efficacy: 73 lumen/watt at 1A
The XR-E was introduced in 2006. It had around twice the efficacy rating (lumen per watt output) of comparable LEDs available at that time. Maximum current of 1000mA with a forward voltage drop Vf = 3.7V.
Cree® XLamp® XR-E EZ900
Viewing Angle: 90°
Chip size: 880um x 880um
LED size: 7mm x 9mm x 4.4mm
Efficacy: 73 lumen/watt at 1A
The XR-E EZ900 is a later revision of the original XR-E EZ1000. It has a smaller LED die with a similar output to the original. Because of the smaller die the EZ900 is favoured for use in longer-throw flashlights (throw improves as the size of the light source approaches a point).
Philips Luxeon Rebel
Viewing Angle: 120°
Chip size: 1000um x 1000um
LED size: 3mm x 4.5mm x 2mm
Efficacy: 130 lumen/watt at 350mA
The Luxeon Rebel is produced by the Philips Lumileds Lighting Company and was first introduced around 2008. Lumileds was originally a Philips & Agilent (HP spinoff) joint venture and produced some of the first power LEDs used in flashlights. Maximum current of 700mA (Vf = 3.2V).
Cree® XLamp® XP-E
Viewing Angle: 115°
Chip size: 980um x 980um
LED size: 3.45mm x 3.45mm x 2mm
Efficacy: 73 lumen/watt at 1A
Introduced in 2008, the XP-E shrunk the footprint of the original XR-E by around 82%, although it uses the same size LED die (with 3 yellow strips and 2 bonding wires). The maximum current is 1000mA with a forward voltage Vf = 3.5V.
Cree® XLamp® XP-G
Viewing Angle: 125°
Chip size: 1400um x 1400um
LED size: 3.45mm x 3.45mm x 2mm
Efficacy: 93 lumen/watt at 1.5A
The XP-G has the same physical footprint as the XP-E but with a 42% larger LED die (with 4 strips and 2 bonding wires). It has a maximum current of 1500mA and a forward voltage Vf = 3.25V. The XP-G has a slightly larger apparent die size because of the built-in optic.
Cree® XLamp® XM-L
Viewing Angle: 125°
Chip size: 2000um x 2000um
LED size: 5mm x 5mm x 3mm
Efficacy: 100 lumen/watt at 3A
Introduced in November 2010. The XM-L has a 4mm sq. die (6 strips and 3 bonding wires) and can be driven to 3000mA (Vf = 3.35V) producing around 950 lumen. The apparent die size is much larger due to the bigger built-in optic and thus is more suitable for floody-beam flashlights.
Cree® XLamp® XM-L2
Viewing Angle: 125°
Chip size: 2000um x 2000um
LED size: 5mm x 5mm x 3mm
Efficacy: 116 lumen/watt at 3A
Introduced in December 2012. The XM-L2 can be driven to 3000mA (Vf = 3.3V) producing around 1198 lumen. The apparent die size is much larger due to the bigger built-in optic and thus is more suitable for floody-beam flashlights. Note that L2 is a component of the part number and that similar bin-numbering applies, eg: XM-L2 (U2).
Cree® XLamp® XP-G2
Viewing Angle: 115°
Chip size: 1400um x 1400um
LED size: 3.45mm x 3.45mm x 2.26mm
Efficacy: 176 lumen/watt maximum
Introduced in mid 2012. The XP-G2 can be driven to 1500mA (Vf = 3.1V). The XP-G has a slightly larger apparent die size because of the built-in optic.

LED Brightness Bin

LEDs are tested for luminous flux and placed into luminous-flux groups (bins).
For example, commonly available XLamp® XM-L white LED groups are:
    Group
    Code
    Min lumen
    @700mA
    Max lumen
    @700mA
    T6 280 300
    U2 300 320

For the XLamp® XP family (XP-E, XP-G), the common luminous-flux groups are:
    Group
    Code
    Min lumen
    @350mA
    Max lumen
    @350mA
    Q5 107 114
    R2 114 122
    R4 130 139
    R5 139 148

Note that the specified lumen output is at a lower current than the maximum allowed current, or even the normal operating current.

Links

The following sites provide reviews or discussion forums on torches+flashlights, information from LED and torch manufacturers:

Reviews

LED Manufacturers

Torch Manufacturers