What's the difference between this and using a voltage meter?

It's not strictly a meter: it's a constant-current power supply with a built-in meter. It provides a constant-current source to light up the LEDs without burning them out. If instead of this box, you put a voltage source on them (like a standard power supply or battery), the current supplied will rise to levels that can destroy the LEDs that you're trying to test (because as they light up, their resistance goes down dramatically). This box senses the resulting current rise and drops back the voltage so that only the current levels normally required to light the LEDs are delivered to the tested components. Unfortunately, too many people selling TV backlight LED arrays on the internet don't know about this phenomenon, and they use standard power supplies to test the arrays before shipping them. The power supplies light up the LED arrays, but if the seller doesn't disconnect the power supply quickly enought, it destroys the LEDs just as the power supply is being disconnected. Then that seller sends that now-broken array to a buyer who won't be able to use it.

Can I use it as permanent power supply?

Pretty much designed for one purpose. Bought my son a 43" Samsung that went blank after one year. It is a lot of work getting to the back lights so this power supply is useful when you get there. Only replaced one out of 3 back light strips. If one led is shorted it pulls down the supply so all lights are out, so each strip can be checked individually to isolate the bad strip. You can build your own supply using batteries but I did not want to be bothered. Will probably never use it again. Btw, when finished, using your TV remote, go to settings and lower your back light power to 50% to go easy on your led's.

ASIN	B078B98QB2
Best Sellers Rank	#520,335 in Tools & Home Improvement ( See Top 100 in Tools & Home Improvement ) #497 in Voltage Testers
Brand	SID LED
Color	Black, Gray, Red, white
Date First Available	December 16, 2017
Is Discontinued By Manufacturer	No
Item Weight	8 ounces
Item model number	GJ2C
Manufacturer	SID LED
Measurement Type	Voltmeter
Min. Operating Voltage	85 Volts
Package Dimensions	7.8 x 3.3 x 2.4 inches
Power Source	Corded Electric
Style	Digital
UPC	613739727386

Lamp and TV Backlight Tester for All LED Lights Repair Output 0-320V

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