Another "black light" that isn't

Wurkkos

PhotonWrangler

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While looking through Wally World recently I stumbled across an A19 LED filament "black light" bulb. Being a UV nerd I picked one up to see if it would be useful for fluorescent mineral stuff. Their P/N is GVLA198K. There is also a TCP P/N WF120008.

It turns out that there's NO UV coming out of this bulb at all - just a dim blue glow. It wasn't able to fluoresce anything and my UV detector card said "nope."

I wanted to see if the dark blue envelope was passing UV by shining a known-good UV flashlight through it and that worked fine. This tells me that the problem is with the choice of LEDs themselves. I'll probably crack this open to see what it's using.

The bulb isn't even useful as a blue lamp since it's output is so dim. Don't waste your money on this one.
 

LEDphile

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While not UV, the 450nm royal blue emitters will excite many fluorescent pigments in a manner similar to a blacklight. As that's usually the LED chip of choice for making white LEDs (in combination with a yellow phosphor), I could easily see some being used as the basis for a consumer "blacklight" bulb.
 

snakebite

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likely its the typical blue leds without the phosphor.
this would explain its uselessness.
one year i put up a 8' ho blacklight for halloween.
had folks posing under it to get picture taken.
lots of everyday stuff glows brightly under a good blacklight.
 

Dave_H

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While not UV, the 450nm royal blue emitters will excite many fluorescent pigments in a manner similar to a blacklight. As that's usually the LED chip of choice for making white LEDs (in combination with a yellow phosphor), I could easily see some being used as the basis for a consumer "blacklight" bulb.
I have a blue-LED flashlight which pre-dates most white-LED flashlights and noticed even at the time it tended to light up day-glow tags, posters etc. although not nearly as well as real UV. I suspect this effect allows vendors of dubious "black lights" some latitude in their claims.

Coloured filament bulbs in one big-box store typically sell for $4-$5 but the "black light" versions go for $11-$12; all that for a coat of clear purple lacquer. The claim of "lights up black" is almost funny (sort of like waking up dead) but not unique as some automotive white-LED products apparently "light up clear".

Dave
 

PhotonWrangler

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"Lights up black" - lol. Yeah I know exactly which bulb you're talking about as I have one of those also. There are a number of bulbs in the $9-$12 range that are near-UV, probably in the 395-405nm range, that will fluoresce things but at reduced contrast because of the visible purple light they put out.

I suspect that this house-branded bulb from Wally World is using white LED filaments instead of blue ones as it doesn't fluoresce anything at all, not even a little bit. I will be cracking this thing open to confirm this.
 

Lark Hunter

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Coloured filament bulbs in one big-box store typically sell for $4-$5 but the "black light" versions go for $11-$12; all that for a coat of clear purple lacquer.

Dave
Walmart and friends didn't even expend the effort to raise the price on this one; I (unfortunately) purchased one to replace a burned out blacklight CFL, and recall the price being about $4.50

^ My guess is going to be ~5000k LED white filaments sulking behind that purple filter. It's pretty sad when an incandescent blacklight bulb puts out more UV than this creation. Gahhbage!
 

PhotonWrangler

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Lark Hunter, you called it right. I cracked it open today and as expected I found phosphor-white LED filaments. I carefully screwed this into a plug base adapter and powered it up, and it lit up a bright cool white, maybe 5000-6000k. This explains why there's no UV coming out of the bulb whatsoever. What a manufacturing blunder.

GVLA19BK_bulb.jpg
 
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