LED Flip Switch powered from USB

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Bunnings sells a battery-powered LED Flip Switch that is very useful and bright. It has 2 COB LED strips with the following specifications:

• Material: aluminum alloy plate + LED COB
• Power: 1W
• Input Voltage ac / DC 2-2.6 (red) 3V-4V (others)
• Maximum current: 300mA (1W) / 1000mA (3W)
• Luminous flux: 100 lm / W
• Lamp Color: cold white (6000-6500K), warm white (2700K-3200K), red (620-630nm), blue (450-460nm)
• Size: 60mm * 8mm
• Lighting area: 50mm * 7mm
• Low attenuation, 1000h attenuation <1%

The light uses 3 AAA batteries for 4.5V and the 2 strips draw combined 600mA which means the batteries will be flattened in around 4 hours(assuming 800 maH per AAA). So why not drive it with 5V from a USB socket? I wired a simple power cable, plugged it into my laptop USB 3.0 socket, measured the current with USB Doctor and found it was drawing 1A.

Well, continuous 1A from a USB 3 socket can't be good in the long run. The light has a current limiting resistor of 0.5 ohm which suited the 3 AAA batteries but obviously was not enough for USB 3. ledcalc.com indicated a 3.9 ohm 1W resistor would be more appropriate but not having one on hand, I paralled 4 x 15 ohm 0.25W resistors to form 3.75 ohm approx 1W as a test.



This brought the current consumption down to 0.46A which was more acceptable.



Update: just bought 3.9 ohm 1W resistors from Jaycar for a more permanent solution.