Black Diamond Gemini, retail $32.95(
Manufactured by Black Diamond Equipment, Ltd (
Last updated 05-15-04

The Black Diamond Gemini is a stout, robust headlamp. It attaches to your head with a 3-point elastic (stretchy) headband, uses two white LEDs and two different kinds of incandescent lamps to produce its light, and uses three AA cells to power it.

The battery pack is on the back of your head (when used as a headlamp), so the Gemini does not have that "front heavy" feel to it that some other large headlamps can have.


Put the Gemini on by placing it over your head, so the lamp portion is in front and the battery pack is in back. The size is adjustable via a buckle assembly on the left side of the headband assembly, and another buckle on the upper headband assembly. I don't review a lot of headlamps here and I'm not a climber or a caver, so please forgive me if I make some eggregious error in describing a strap or a buckle. The headband is elastic (stretchy), so you don't have to get things *exactly* right for the Gemini to fit properly.

To operate the Gemini, press and release the button on the underside of the Gemini's lamp head; this turns the two white LEDs on. Press and release it again to turn the Gemini off. Press and release it again to turn the incandescent lamp on, and press and release it a fourth time to extinguish the Gemini.
Just like it reads on the back of the shampoo bottle; lather, rinse, repeat. In other words, the Gemini starts over with the LEDs when you use the button again. Then it turns off. Then the incandescent bulb turns on. Then it turns off again.

The Black Diamond Gemini on a flashlight tester's head.

Once you have it fitted to your head, you can adjust the angle of the Gemini by pivoting the light body up or down as you see fit.

To change the batteries in your Gemini, find and hold the battery compartment. Orient it so the rubber portion faces up. That part of the strap that goes over this part, pull it up - a couple of inches of it anyway. At the end of the battery compartment not attached to the upper headband, lift up on the rubber lid, and peel it away as necessary.

If necessary, remove and dispose of or recycle the three used AA cells in this compartment.

Insert three new AA cells in this compartment, following the polarity markings embossed in each battery chamber. Place the rubber lid over the battery compartment, and press in on its edges to seal it shut. Pull on the lamp portion of your Gemini so that the head strap loop you pulled out earlier goes back down over the rubber battery lid.
There. Done with that.

Black Diamond defines "usable light" as light bright enough to see and identify something at the bottom of a backpack, light your feet when climbing, or see well enough to tie a knot and set up a rappel; all at night of course. ;-)

Half of the Gemini's light comes from an incandescent bulb, and eventually it will blow out and need to be changed. To do this, unscrew and remove the front portion of the lamp assembly (the bezel and window assembly), and set that aside. Remove the reflector, and set that aside too. Pull the burned out bulb straight out of its socket, and stomp on it (if you like to hear things pop) or dispose of it (light bulbs can't be recycled - not yet anyway). Using a piece of tissue or bungwipe, insert a new bulb, pins down, straight into the two holes in the bottom of the lamp assembly for it. Push it straight down without twisting until it stops. Place the reflector back on, aligning the two holes in it with the two LEDs in the lamp assembly. If the reflector is installed correctly, you'll easily be able to push it down flush with the top of the lamp assembly. If it doesn't fit flush when GENTLY pressed, turn it 180 degrees and try it again. Place the bezel back on the front of the lamp assembly, and screw it on until it's firm. Do not try to overtighten it, or it will probably become broken.
If you stomped on the old bulb instead of throwing it away, be sure to sweep up the broken glass and get rid of it. You don't want to step in it barefooted later. :-)

The Gemini comes with two incandescent bulbs: the low output one already installed, and a high output one stored in the battery compartment. You can swap them anytime as you see fit. There is a blue transparent plastic thing over the glass on the bulb stored in the battery compartment; do not forget to remove that after lamping the Gemini with this bulb, and slide it on the bulb you're putting back in the battery compartment.

Xenon-filled incandescent light bulbs do not like to be touched with bare hands or any other bare body part, because skin oil on the glass can cause the bulb to explode or otherwise fail when it is subsequently used. That's why I suggested using kleenex or toilet paper to handle the bulb during replacement. If the bulb was touched with your fingers or other bare skin, wash it off with pure alcohol (tape or disk head cleaner works well for this) on a bit of kleenex or buttwipe before reassembling your Gemini.

The Gemini appears to be at least reasonably durable; in that ordinary flashlight accidents should not do it in. The steel rod I use for "whack testing" is on a table hosting a running test; striking the Gemini against that rod right now would likely queer the test, so I cannot do the whack test right now. Not when that test running now is about to enter its fourth day, anyway.

I believe the Gemini is weather-resistant, but not waterproof or submersible. There IS an O-ring between the bezel and lamp assembly, so I believe at least that part of the Gemini is weather-resistant enough to stay dry when the light is used in rain or snow. But I don't believe the battery compartment is submersible; if it falls into water or if the dog pees on it, it may leak. I didn't say it WILL leak, but it MAY.

More later...let me FTP this page up for the time being...

Beam photo (LEDs) at ~12".
Measures 28,300mcd.

Beam photo (Incandescent, low output) at ~12".
Measures 152cd.

Beam photo (Incandescent, high output) at ~12".
Measures 282cd.

All tests were performed on a Meterman LM631 light
meter, using the batteries that came with the Gemini.

Test sample was purchased on Ebay on 05-09-04, and was received on 05-12-04. The link I bought it from is right here. When the link expires on 08-09-04, use the View seller's other items page to see if they're still selling the Gemini.

UPDATE: 00-00-00

Easy, tool-free battery change
Appears to be reasonably durable

May not be entirely water-resistant - but I have no proof just yet.

    MANUFACTURER: Black Diamond
    PRODUCT TYPE: Medium to larger sized headlamp
    LAMP TYPE: 5mm white LED, incandescent bulb
    No. OF LAMPS: 3 (two LED, one incandescent)
    BEAM TYPE: Varies, depending on the lamp used
    SWITCH TYPE: Pushbutton on/off on underside of light
    BEZEL: Rubberised plastic; LEDs, incandescent lamp, and reflector protected by plastic window
    BATTERY: Three AA cells
    CURRENT CONSUMPTION: Unknown/unable to measure
    WATER RESISTANT: Yes, weather-resistant at minimum
    ACCESSORIES: Batteries
    WARRANTY: 3 years


    Star Rating

Black Diamond Gemini *

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