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Old Dec 21, 2013, 11:12 PM   #1
Join Date: Nov 2009
Posts: 52
Default photo lamp tip: 'UFO Lantern' tent light (how to modify)

I was long time looking for a simple photo lamp that takes little space, can render blue, illuminates about 1.5m and doesn't run hot. I mainly need it to document electronics. So I now tried a very cheap battery operated LED camping light. I bought this specimen a year ago for 2.99 at the German shop KiK with the meaningless name "LED Leuchte" (= LED luminaire), but you can find many variants online with the brand name "UFO Lantern". The diameter is 14.5cm and mine has 36 LEDs (also other counts exist). They run pretty bright on 4 standard AA cells and the colour temperature resembles daylight.

The bad thing is that the Chinese plastic construction is flimsy with loose electric parts inside, and the white LEDs have no proper current limiter (likely voltage regulators inside each LED chip) and so draw >1A at 6V with full batteries. All LEDs are wired parallel. The case bottom is held by a bajonet mechanism. You have to turn it about 20 counterclockwise (against depicted arrow direction) to open and clockwise to close (do not confuse or use force - it may break). Mine has 2 small magnets on the back to stick to a metal surface.

Most bizarre is that the power consumption is almost independent from the power switch setting, which can light either the 12-LED or 24-LED ring or both, i.e. 12 LEDs draw as much power as 36, which can't be good for them (and doesn't make them really brighter than whith both rings lit). When fed with full NiMH rechargebles, the current even raised above 1.7A which was certainly harmful for LED longevity.

So I took the thing apart and tried 1A silicon diodes (e.g. 1N4007) to drop the voltage (each by 0.7V) to an acceptable level. For this I rewired the switch (be careful not to melt its cheap plastic while soldering). I wired both LED rings permanently parallel and installed 1 diode always in series. Unlike resistors, diodes waste no energy with heat production, which increases battery life. The push button switch has 2 independent contacts and 4 settings {none,1,2,1+2}. I used them to wire either 2, 1 or no additional diodes in series to adjust brightness. So I get very useable brightness control:

0 = off (interrupted)
1 = 3 diodes (80mA, like cheap flashlight)
2 = 2 diodes (400mA, useful for photos)
3 = 1 diode (1A, roughly like 25W incan spot)

Important is to use the "both contacts parallel" position for 1A to avoid switch damage. At 1A already the resistance of the cheap internal wiring reduces brightness, so I installed a thicker wire, and insulated important parts with hotglue and fixed loose battery contacts with it to avoid shortcircuit, which else may set the thing on fire with high power rechargebles installed. I still don't recommend to keep them installed when not in use (something may break and short). I read internet complaints that the switch of these things tends to break; if the plastic bridge or screw post breaks, use hotglue.

When modded, the UFO-Lantern is a very useful photo lamp. Already at 80mA it is bright like a cheap household torchlight with full battery (sufficient for closeups) but has much nicer light distribution due to the large diameter. You can use this mode also to conserve battery while arranging a scene. At 400mA I already can take tripod photos with the lamp in the other hand held an arm length away. At full 1A it is such dazzling bright (but way less unbearable than a 10W LED single chip spotlight) that my digicam (Samsung WB210) already tends to overdrive when too close.

The colour rendition is of course not exactly daylight, but much closer than the ceiling incan (likely somewhere about 6500K), so I can use "cloudy" or automatic white balance mode of the camera. Blue is a bit more intense and as usual with such LEDs (those transform blue light into yellow) and brown wood has a strange yellowish hue. But it is definitely enough to document electronics. Only the still limited lamp size makes harder shadows than daylight from a window, but it is way superior to my small head lamp. Another application may be to photograph or film through the center hole (like a ring flash - haven't tried to avoid reflections).

This is an example photo how electronics (inside of a music keyboard) looks when photographed in my otherwise almost dark kitchen. The "UFO Lantern" was held in my left hand in the left front corner of the picture. The digicam mounted with clamp tripod on chair backrest.

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MAY THE SOFTWARE BE WITH YOU! *============================================================================* I CYBERYOGI Christian Oliver(=CO=) Windler I I (teachmaster of LOGOLOGIE - the first cyberage-religion!) I I ! I *=============================ABANDON=THE=BRUTALITY==========================* {http://weltenschule.de/e_index.html}

Last edited by CYBERYOGI =CO= Windler; Dec 21, 2013 at 11:39 PM. Reason: example photo added
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Old Dec 21, 2013, 11:23 PM   #2
Join Date: Nov 2009
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Here is some colour comparisons between genuine daylight and the battery operated "UFO Lantern".


UFO Lantern:

The latter 2 were on "cloudy" white balance settings and look surprisingly neutral.
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