LED bulb handy for custom setups

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BugEZ
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LED bulb handy for custom setups

Post by BugEZ »

I have been making a time lapse movie of fly larva as they develop inside a small terrarium. The rig’s purpose was to photograph seed germination. The unexpected larval visitors proved to be more interesting. My “two to three week” project has been clicking away for several months now.

I recently “upgraded” the LED lights that pulse on during exposures. I had been using 4 discrete 5mm white LED bulbs. With these I used a 0.600 second exposure (~f4) as they were quite dim. The long exposure was not a problem with seeds, but with squirming larva I needed something shorter. I discovered 12V LED bulbs a local home improvement store. Each bulb is ~40X brighter than the discrete 5mm LEDs. They also have current limiting built in and can operate on 12V AC or DC. I believe they are intended for landscape illumination. With two of these bulbs replacing 4 5mm LEDs I have been able to reduce the exposure time to 0.060 seconds, and to stop down to ~f6 improving depth of field.

Here is a picture of the bulb in the quickly built cardboard reflector. It is about 1.4 inches tall.
Image

Here is a link to the bulb’s description

https://www.menards.com/main/electrica ... 0&ipos=20

I drive the bulbs using a small 12V DC adapter “vampire” rated at 1 amp. 12V power is switched by a programmable timer/ controller triggered by the camera’s hot-shoe contacts. Each bulb draws about .25A

I am not certain of the bulb’s whiteness rating. I did a custom white balance and the images of larva and soil look ok. The sharpness improved, and I confirmed I was watching fungus gnats.

A link to a YouTube video of the gnats.

https://youtu.be/aqlHC1awavA

What larks!
Last edited by BugEZ on Wed Dec 11, 2019 7:22 am, edited 1 time in total.

kutilka
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Post by kutilka »


BugEZ
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Post by BugEZ »

Thanks kutilka for fixing the link. Not sure what went wrong there. I went ahead and edited my post adding a space after the url before the trailing BBC code and it appears to work now...

Keith

ray_parkhurst
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Post by ray_parkhurst »

The linked light is different from the one you pictured. Do you have a link to the ones with 5 COBs?

A few thoughts on these...They claim a CRI of 100. This makes me curious, since these bulbs are designed for AC operation. They don't have any sort of DC filtering (no room for it) so probably drive the rectified AC directly to the LEDs, with current limiting resistors. In general I've seen a significant variation in color temp from COB and other "white" LEDs versus current drive levels. Could it be that running LEDs off of AC, which would run them dynamically over the full current range from turn-on ("0") up to more than their maximum at 12V, may actually spread the spectrum and improve the CRI? Another consideration is that COB phosphors have varying decay times, so if AC is applied, the spectrum will vary vs time, and the first half of rectified AC will have a different spectrum vs the second half. Thus if these are used for photographic work using AC, for short exposures, color temp may be different depending on the position in the AC cycle. Of course if you run on DC, the color will be constant, though maybe the CRI will be worse?

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Post by rjlittlefield »

Google search on BP20G4 finds numerous sources.

The manufacturer's page is https://www.feit.com/product/170-lumen- ... le-led-g4/ .

Amazon has them at https://www.amazon.com/Feit-Electric-BP ... B081BT6T42 .

I don't see a CRI specification at either of those places.

Note that the bulbs come in both 5000K and 3000K versions, both are BP20G4 but then 850 versus 830.

--Rik

rjlittlefield
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Post by rjlittlefield »

About the URL's, I did not see them when they were broken so I can't tell for sure what went wrong.

But I've added some information to the FAQ, see here: https://www.photomacrography.net/forum/ ... 421#256421 .

--Rik

ray_parkhurst
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Post by ray_parkhurst »

rjlittlefield wrote:
I don't see a CRI specification at either of those places.
I was referring to the original linked LED, which specifies the CRI 100 rating.

chris_ma
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Post by chris_ma »

ray_parkhurst wrote:
rjlittlefield wrote: I don't see a CRI specification at either of those places.
I was referring to the original linked LED, which specifies the CRI 100 rating
a CRI of 100 is impossible (at consumer cost at least, might be possible at lab technology cost) with todays LED technology.
there seem to several mistakes on the original linked page. they list:

Code: Select all

Product Type - Linear Halogen Light Bulbs
yes, a CRI of 100 is possible (actually easy) with halogen. but the bulb in the picture and the title is a LED.

Code: Select all

Incandescent Wattage Equivalency - 20 watt

Code: Select all

Bulb Wattage - 20 watt
yes, incandescent lights with 20W have an equivalent of 20W incandescent lights ;)
Light Output - 170 lumen
about 9 lumen/watt, typical efficiency for incandescent lights
Color Temperature - 5000 kelvin
no incandescent/halogen light will reach 5000K (highest is usually about 3400K at reduced lifespan).

so the specs seem to be a mixup between LED and Halogen/Incandescent tech.

the best LEDs I've found so far are by waveform lighting. they list a CRI of 99 and show paperwork to back it up. I have both the 5000K and 6500K variants and they are great.

they also have a page with nice graphs explaining about CRI:
https://www.waveformlighting.com/full-s ... d-lighting

chris

BugEZ
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Post by BugEZ »

Here are front and back photos of a spare bulb. Note the 170 lumen, 12V, 170mA markings. The bulb measures 1.125” top to base excluding pins.

Image

Image

Keith

chris_ma
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Post by chris_ma »

BugEZ wrote:Here are front and back photos of a spare bulb. Note the 170 lumen, 12V, 170mA markings.
yup, that's about 2W total on 10 dies. not terribly high power but otherwise they probably run into thermal issues.

these kind of LEDs usually have a CRI of 80-90, a quick test is to hold an object with dark saturated red in front of it and then in front of a halogen (or daylight) and see how big of a change you get.

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Post by rjlittlefield »

ray_parkhurst wrote:
rjlittlefield wrote:
I don't see a CRI specification at either of those places.
I was referring to the original linked LED, which specifies the CRI 100 rating.
Advertisements are not always to be trusted. The original link goes to Menards, and yes, it says both "Feit Electric BP20G4/850/LED" and "CRI rating of 100".

But on the manufacturer's page for that product, I see no mention of CRI, and when I download the specifications from https://www.feit.com/wp-content/uploads ... cSheet.pdf, that document says "CRI >80".

So, I'm thinking that somebody at Menards took a little creative license with the specs.

Note that the model number clearly shows on Keith's first image.

--Rik

ray_parkhurst
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Post by ray_parkhurst »

rjlittlefield wrote: Advertisements are not always to be trusted. The original link goes to Menards, and yes, it says both "Feit Electric BP20G4/850/LED" and "CRI rating of 100".

But on the manufacturer's page for that product, I see no mention of CRI, and when I download the specifications from https://www.feit.com/wp-content/uploads ... cSheet.pdf, that document says "CRI >80".

So, I'm thinking that somebody at Menards took a little creative license with the specs.

Note that the model number clearly shows on Keith's first image.

--Rik
For sure when you read a CRI of 100 it must be taken with a grain of salt, but I did find it interesting that an AC-supplied LED would have such a high rating, true or not. Generally I would have expected a lower rating for AC supply. The >80 spec is more believable, but also much less valuable as a replacement for an incandescent bulb.

I did not look for the part number, instead putting the onus for a proper product link back to the OP.

chris_ma
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Post by chris_ma »

ray_parkhurst wrote:For sure when you read a CRI of 100 it must be taken with a grain of salt, but I did find it interesting that an AC-supplied LED would have such a high rating, true or not. Generally I would have expected a lower rating for AC supply. The >80 spec is more believable, but also much less valuable as a replacement for an incandescent bulb.
I don't see why an AC power LED would have a different CRI then one on DC power.
firstly the AC powered one just has a built in DC converter anyway, and even if that would be of poor quality that would mainly result in possible flicker and not change the CRI at all.

CRI in white LEDs is a result mostly by the selection of the blue LED and mix of phosphors.

chris

ps: an a CRI 100 claim doesn't have to be taken with a grain of salt, we can pretty much be sure it's either a marketing lie or an unintended error ;)

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Post by ray_parkhurst »

chris_ma wrote:
ray_parkhurst wrote:For sure when you read a CRI of 100 it must be taken with a grain of salt, but I did find it interesting that an AC-supplied LED would have such a high rating, true or not. Generally I would have expected a lower rating for AC supply. The >80 spec is more believable, but also much less valuable as a replacement for an incandescent bulb.
I don't see why an AC power LED would have a different CRI then one on DC power.
firstly the AC powered one just has a built in DC converter anyway, and even if that would be of poor quality that would mainly result in possible flicker and not change the CRI at all.

CRI in white LEDs is a result mostly by the selection of the blue LED and mix of phosphors.

chris

ps: an a CRI 100 claim doesn't have to be taken with a grain of salt, we can pretty much be sure it's either a marketing lie or an unintended error ;)
Phosphor color is LED intensity-dependent, and since the current in the LED varies over a wide range, I'd expect some CRI variation vs position in the AC current cycle. Different phosphors have different emission time constants as well, so that may also shift the color a bit.

chris_ma
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Post by chris_ma »

ray_parkhurst wrote:Phosphor color is LED intensity-dependent, and since the current in the LED varies over a wide range, I'd expect some CRI variation vs position in the AC current cycle. Different phosphors have different emission time constants as well, so that may also shift the color a bit.
hmm, I'm not so sure about that. Usually one can drive even white (ie blue led with yellow phosphor) with PMW without significant color shift.

From what I've read the main cause of color shifts are binning to start with (ie manufacturing tolerances) and temperature (obviously PMW and current can have a significant effect on temperature).

But even if they shift colors, the effect on CRI will be very small since the main problems are usually the gaps in cyan (around 480nm) and deep red (over 630nm), which won't be affected a lot by temperature/current (they will shift a few nm, but the gaps will still be there)

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