Tests of different DIY household bulb solutions

[LEDTonic]

How much are you guys spending setting up these lights? Just seems like it may be close to what it would cost to build a cob light, which is more efficient and puts out less heat.

I am not growing with any of these bulbs, or am even intended to do so. I design and sell LED grow light panels/lamps and grow a lot with those, but this thread is not about them :). I've just seen many growers use household bulbs but without having any data of how much they are putting out and what distance they should be used at to achieve a certain intensity.

These tests mainly started out with the idea that I am not fond of the CFL-technology (e26/27), partly because it is inefficient (in lm/w), spreads the light inefficiently (PPFD/w), but also because they contain mercury.

I am just trying to help growers solve intensity-problems. For example, many have a single small succulent plant or other ornamental that needs artificial light to survive during the winter. Obviously, there is no need for a huge grow light panel that chews away at 150 watts with only blue and red diodes, creating a completely purple living room. Instead, a 5-14w bulb could be the perfect match for a small single plant, hung at 3-10", depending on the intensity needed.

Same goes for starting cannabis seeds. The intensity required early on can easily be covered with a 14w bulb, or even 9w (not to mention a 2,2w bulb that I am about to test). When a lot of power is needed to cover a big area, I would instead recommend a proper grow light since they are made for the purpose and oftentimes are a lot more efficient at 150+ lm/w, than regular LED household bulbs performing at 85-110 lm/w. Why hang a huge grow lamp very high above a couple of small plants when the job could be done with one or a few small household bulbs a lot closer to canopy. Even more practical and logical for a plant with a 24/0 photoperiod.

Everyone should use the technology they are most comfortable in using. I am only creating maps and information for the average Joe to easier see and choose the proper lighting for his/her situation and needs.
DIY'ing a real grow light is obviously great and gives a very good lamp. I am with you on that one. Although it's not for everyone.

When I did the 17-measurement 2x2' grid, I noticed it usually wasn't uniform. The north side might have stronger readings than the south. (Maybe the socket wasn't hanging perfectly straight. I should slip an iron pipe over the cord, let it rest on the top of the socket housing. Maybe it would plumb itself better.).

I like where this discussion headed, light and measuring is very interesting.

To be able to closely compare bulbs in a good way, I agree with you on your theory and thinking. Although if you are being this exact in your measuring, you might want to consider mounting your lamp to something, instead of having it hanging with and added weight on it.
This is just a pair of barbeque sticks and a pretty bad example, but you get my point.

It also needs to be very carefully centered over your map or it could give uneven values, I guess. Especially important if you are going to measure at certain spots in every test.
As you can see on my maps, I did not manage to centre the bulb perfectly, or they were uneven/leaning slightly.

I choose 6" height as I tried to find a good seedling-intensity at around 100-175 PPFD, with a good bulb (9w for $1,5), as I think that's what these bulbs are suited best for.

If the intended use of your achieved measurements will be situations that require more than seedling-PPFD, such as growing a whole CB plant, it may be more useful to measure the bulbs at a greater distance as this could potentially make it easier to calculate overlapping intensities and give a better whole picture (depending on the wattage).

If your intended use of measuring is just to compare bulbs, for the sake of comparing bulbs, I guess there are a lot of ways to do so.
I would love to get an update when you get your tools. Even though we seem to be on slightly different missions, It has been very interesting to share thoughts :).

 

[az2000]

Although if you are being this exact in your measuring, you might want to consider mounting your lamp to something, instead of having it hanging with and added weight on it.

My thinking has been that hanging the socket from its power cord lets gravity do the centering (although more weight might be desirable). And then I can drop a plumb line straight down from the socket to find the geometric center. I never used the lux meter to find the point with the highest intensity, and call that center. Maybe that would be better.

I'm reluctant to build a stand/mount. It would probably turn into more than it needs to be.

If your intended use of measuring is just to compare bulbs, for the sake of comparing bulbs, I guess there are a lot of ways to do so.

That's all I want to do. I just want to compare lightbulbs, be able to conclusively say which one is "best" (PAR/w, which should translate to best spectrum.). It might be useful to compare to more serious lighting. But, I think the attractiveness of these lights is that they're easily available (and use standardized mounting hardware that can be reused forever. Plug-n-play.). The quandry is which brand to buy. It would be nice if they're all virtually the same. That was my premise when measuring Lux. I figured that was close enough to compare white-light bulbs (not comparing blue/red lights).

I'm curious to see how they differ (and how today's bulbs compare to the ones I used 3-4 years ago to grow that one plant through flower.). I wanted to buy a PAR meter back then. I like gadgets. I'm glad I waited. Back then the sensor didn't measure far red & blue. It more abruptly cut off both sides. I noticed that's been improved a little.

 

[LEDTonic]

My thinking has been that hanging the socket from its power cord lets gravity do the centering (although more weight might be desirable). And then I can drop a plumb line straight down from the socket to find the geometric center. I never used the lux meter to find the point with the highest intensity, and call that center. Maybe that would be better.

I'm reluctant to build a stand/mount. It would probably turn into more than it needs to be.



That's all I want to do. I just want to compare lightbulbs, be able to conclusively say which one is "best" (PAR/w, which should translate to best spectrum.). It might be useful to compare to more serious lighting. But, I think the attractiveness of these lights is that they're easily available (and use standardized mounting hardware that can be reused forever. Plug-n-play.). The quandry is which brand to buy. It would be nice if they're all virtually the same. That was my premise when measuring Lux. I figured that was close enough to compare white-light bulbs (not comparing blue/red lights).

I'm curious to see how they differ (and how today's bulbs compare to the ones I used 3-4 years ago to grow that one plant through flower.). I wanted to buy a PAR meter back then. I like gadgets. I'm glad I waited. Back then the sensor didn't measure far red & blue. It more abruptly cut off both sides. I noticed that's been improved a little.

Sweet. You are an unsung hero, carrying out these tests and comparisons. I'd like to know how practical you find it to be with a pipe as added weight and I might implement that myself if it does what we want it to.

By the way, do you have a set period of time that you are having the bulbs lit before you measure them? The intensity of light decreases as heat builds up (in LEDs).
I did wait a couple of minutes with the CFLs as they light up slowly, But when the map had been drawn and I was going to confirm and film the footprint, the intensity seemed to have decreased and didn't match with the drawing, which seemed strange.

 

[az2000]

By the way, do you have a set period of time that you are having the bulbs lit before you measure them? The intensity of light decreases as heat builds up (in LEDs).

I don't recall what I did. I think I waited for it to stabilize. I remember in some cases it didn't stabilize very well. The meter fluctuated as it sat there, like the light was pulsing slowly.

While this topic was fresh on my mind, I created this spreadsheet to show the metrics in a standard way. The area and distance may change.

Last time I didn't measure actual watts. That might be useful (instead of assuming the info on the box is accurate).

 

[LEDTonic]

I don't recall what I did. I think I waited for it to stabilize. I remember in some cases it didn't stabilize very well. The meter fluctuated as it sat there, like the light was pulsing slowly.

While this topic was fresh on my mind, I created this spreadsheet to show the metrics in a standard way. The area and distance may change.

View attachment 882082

Last time I didn't measure actual watts. That might be useful (instead of assuming the info on the box is accurate).

That looks awesome, have you already received the quantum sensor?
I am looking forward to seeing the results and what differs the different bulbs.
Indeed, the exact wattage is also interesting.

Hopefully, I will get time to measure and film video #2 in the coming days, and deliver results on a couple of new lamps.
I am excited to measure the IKEA grow bulb. It actually delivers a decent intensity at a decent distance because of the 30 degree focusing lenses, but the footprint is not very impressive.

 

[az2000]

[In fairness: I haven't looked at household LED lightbulbs during that period either. ... Revisiting that topic recently, I see Cree & Philips have replaced their lightbulbs with what appear to be lower-performing bulbs. So, maybe it's not as attractive as it was. I'm looking forward to measuring PPFD soon. I'll buy new bulbs and baseline things again (compare the bulbs from 3-4 years ago).]

Update: I spent more time looking at the new Cree & Phillips lightbulbs.

- I think Philips has the same bulbs as I bought before, but now they're called "Warm Glow" (for their dimmable effect). The specs suggest it's the same bulb (same L/w).

When I looked a couple days ago, I saw their "value line." Non-dimmable (which is fine), but lower L/w. (I should still test one of these without the globe to see how it compares. Maybe it's PAR performance would be better than its L/w suggests.).

- Cree's lightbulbs are lower L/w. But, they have a CRI 90+. I think I've read higher CRI makes a light source better for growing. Maybe I'll see that measuring PAR.

I was disappointed to see CREE discontinued its 95w/18w actual PAR38 3000k, 1500 lumen, 47-degree floodlight. I really liked that light. CREE's replacement is either a 120w/19w 3000k, 1200 lumen flood, or 150w/19w 3000k, 1500 lumen flood. Both are 40-degree.

This is confusing because the old 95-w equiv had 1500 lumens and was considered a 95w-replacement. Now the same lumens is a 150w-replacement. And, the lower-lumen floodlight uses the same amount of watts.

But, looking at these newer floods more closely: they might be good. CRI 90+ (I don't know what the old one was.). And, the lens is plastic (not glass like the old one). It may be possible to cut that off, improving the output. The old design had diodes facing sideways elevated on a pillar. The new design has them facing forward. So, that might be some strong light without the lens.

 

[az2000]

Indeed, the exact wattage is also interesting.

I just saw this video of one of the Philips lightbulbs I tested a 3-4 years at. It's a 8.5w (2700k) model 9290011350:

It shows the actual watts stabilized at 7.8w. That's over 100L/w (based upon the box's stated 800 omni-directional lumens with the globe attached. However, this is meaningless with the globe removed, measuring directional light landing on a surface.). That's higher than other 60w-equiv bulbs (based upon the info on their boxes). Usually they're in the 80-90 L/w range.

That's a really good light. I'm looking forward to measuring it's PPFD. (I should have my PAR meter Monday).

I see that bulb for sale online. But, the Philips web site doesn't show it among their products. This is confusing because their newer(?) non-dimmable bulb (461129) is also sold online as 8.5w. But, it's not shown on the Philips product page either. (Even more confusing: the spec sheet says it's 10w. I found that spec sheet searching the Philips site.).

So, I think it will be important to report actual watts used, and any identifying model numbers.

 

[az2000]

Here's my self-plumbing lamp socket:

That's an 18" iron pipe, 1" threads. I have:

- 1" female pipe-thread PVC "cap" on one end (with a hole drilled for the power cord to pass through. The hole should be centered so it won't kick the pipe into an angle.).
- 1" pipe-thread PVC fem-fem coupling
- 1" pipe-thread PVC "plug." This plug has a 3/8" hole drilled through it. I used a 1" long 1/8" NPT nipple (standard light socket hardware) to mount the socket tightly to the plug. There's a nut inside the plug, tightening the socket against face of the plug.

That socket will accept 5-1/2" & 8-1/2" reflectors

I have one of these corner levels from Harbor Freight:

It has magnetic strips on the inside. It attaches itself to the pipe! Suspending the pipe by the power cord, it appears to be plumb. (Inside the socket there are "ears" which the wires are supposed to go under. This prevents the weight of the pipe from pulling the wires out.).

I think that will work for what I'm doing . 18" iron pipe might be heavier than necessary. I just wanted some weight to overcome kinks in the wire. I have ceiling fans which I can hang this from. I can make a loop in the wire (and use a spring clamp to secure it together) for height adjustment.

I had some ideas about making a stand that could allow for perfect leveling. But, this should be good enough. As long as the light is low enough that most of the light is hitting the measured grid. If there were a slight angle, the average PPFD/w will be the same. I'm not sure it could ever be perfectly plumb/square. The threads inside the socket are a little loose/sloppy.

 

[LEDTonic]

Here's my self-plumbing lamp socket:

View attachment 882387

View attachment 882386


View attachment 882384

That's an 18" iron pipe, 1" threads. I have:

- 1" female pipe-thread PVC "cap" on one end (with a hole drilled for the power cord to pass through. The hole should be centered so it won't kick the pipe into an angle.).
- 1" pipe-thread PVC fem-fem coupling
- 1" pipe-thread PVC "plug." This plug has a 3/8" hole drilled through it. I used a 1" long 1/8" NPT nipple (standard light socket hardware) to mount the socket tightly to the plug. There's a nut inside the plug, tightening the socket against face of the plug.

That socket will accept 5-1/2" & 8-1/2" reflectors

I have one of these corner levels from Harbor Freight:
View attachment 882388

It has magnetic strips on the inside. It attaches itself to the pipe! Suspending the pipe by the power cord, it appears to be plumb. (Inside the socket there are "ears" which the wires are supposed to go under. This prevents the weight of the pipe from pulling the wires out.).

I think that will work for what I'm doing . 18" iron pipe might be heavier than necessary. I just wanted some weight to overcome kinks in the wire. I have ceiling fans which I can hang this from. I can make a loop in the wire (and use a spring clamp to secure it together) for height adjustment.

I had some ideas about making a stand that could allow for perfect leveling. But, this should be good enough. As long as the light is low enough that most of the light is hitting the measured grid. If there were a slight angle, the average PPFD/w will be the same. I'm not sure it could ever be perfectly plumb/square. The threads inside the socket are a little loose/sloppy.

Nice! You truly did a great job and I am also a bit amazed about the corner levels as that was new to me.
I used a rope ratchet to adjust heigh and a clothes rack that it was all attached to. A spring clamp might be even better and more exact.
Really looking forward to when you get your order delivered. Let's hope for Monday :)

 

[LEDTonic]

When I did the 17-measurement 2x2' grid, I noticed it usually wasn't uniform. The north side might have stronger readings than the south. (Maybe the socket wasn't hanging perfectly straight. I should slip an iron pipe over the cord, let it rest on the top of the socket housing. Maybe it would plumb itself better.).

I feel like all sides should be measured. If just one side, and if a diode were mounted with a minuscule angle (or, the socket isn't perfectly plumb, or socket's threads are a little wobbly), then it's random if the good (or bad) side is being reported.

I like the idea of keeping it simple. My 17 measurements seemed like overkill for a household bulb. But, the risk is missing a spot that might reflect better on the bulb.

I'm thinking measuring the bulb *closer* to the surface would be better. Like your 6" distance. That's comparable to the distance I mount 9-10 (60w-equiv) bulbs from the leaves. A 15-16w (100w-equiv) might be 8-10". (I didn't use those very much. I liked to use lower-watt lightbulbs -- but more of them, spreading the light over the plant, better/even coverage). A 19-20w PAR38 floodlight would be 12-16".

So, my 18" distance is probably too much. I the light were more concentrated, the 24" corners wouldn't be as meaningful. You're 6" distance has me thinking about measuring a 6" box inside a 12" box (17 measurements again, but a smaller footprint with fewer irregularities between measurements. The light should be more uniform if it's tighter together/focused.).

One thing that concerns me about being too close: hitting the exact measurement points could be tedious. Being just 1/8" off could alter the value (whereas, when the lamp is 18" above, 1/8" lateral movement wouldn't be as great (relatively speaking).

I'll have to play with it. I'm imagining how it would work. I won't know until I try.

EDIT: I like the idea of measuring to the LEDs regardless of globe, reflector. PAR38 floods/spots may have suspended LEDs (mounted on a post). That might complicate things.

I just stumbled upon a picture of the first map I made, where I measured every inch and made small dots with a pencil, which I afterwards filled in with a sharpie.
Thought you might be interested in how it looked like.

 

[az2000]

I just stumbled upon a picture of the first map I made, where I measured every inch and made small dots with a pencil, which I afterwards filled in with a sharpie.
Thought you might be interested in how it looked like.

Thanks. It's hard to know how best to measure these lightbulbs (what's "good enough."). Also, thanks for mentioning the ratcheting light hanger. I'm sure that's how I did it 3-4 years ago. (When I started to anticipate measuring again, I couldn't remember how I hung the socket. I was thinking I'd adjust the length of the electrical cord with a loop, and clamp the intersection of the cord together to hold that length. It never crossed my mind to use one of the 20 ratcheting lamp hangers I have.).

My PAR meter arrived today. I have a couple things I want to finish before I get into that.

I need to go to the store and buy new lightbulbs. I want to start fresh. Keep track of how long a bulb is used (growing), measure it again to see if it loses its brightness. I probably have a couple unused bulbs from back when I started using them. But, I didn't keep track of which bulbs were used in which grows, etc. I can't estimate how many hours a bulb has on it. I should probably throw them away and start over.

 

[LEDTonic]

It's hard to know how best to measure these lightbulbs (what's "good enough.")

It depends on what you plan to do with the results and who you are going to show them to, other than what you feel covers your own interests.

I just recently recorded a video about planting seeds and other generally fun stuff (which is irrelevant). The natural lighting was insufficient and I came up with this solution.
This is also how I will be doing the next video in which I will measure new bulbs.
Since you have some measuring ahead of you, I thought you could benefit from my idea. Clothes rack + table can really spare you from some sore knees and back :)

 

[az2000]

Have you seen this inexpensive DIY Public Labs Lego Spectrometer. (<<link). I bought one a few years ago (but the design was different. The housing was a large electrical "conduit body." It worked well. The online "workbench" graphing software allowed for downloading the data to process/graph it differently.

I thought that could be a way to evaluate/compare LED grow lights (and lightbulbs) in a standardized way. I just saw this video showing how to make a spectrometer. He talks about his interest in evaluating grow lights.

He works with this Theremino project/DIY spectrometer. (<<link).

He has a newer model here, (<<link) with a video showing how it works.

 

[LEDTonic]

Have you seen this inexpensive DIY Public Labs Lego Spectrometer. (<<link). I bought one a few years ago (but the design was different. The housing was a large electrical "conduit body." It worked well. The online "workbench" graphing software allowed for downloading the data to process/graph it differently.

I thought that could be a way to evaluate/compare LED grow lights (and lightbulbs) in a standardized way. I just saw this video showing how to make a spectrometer. He talks about his interest in evaluating grow lights.

He works with this Theremino project/DIY spectrometer. (<<link).

He has a newer model here, (<<link) with a video showing how it works.

Wow, that looks amazing. I can imagine how fun it would be to have one.
Have you had any chance to play with the MQ yet?

 

[az2000]

Have you had any chance to play with the MQ yet?

Not yet.

I bought some bulbs today. I got two Cree lightbulbs. I'm curious to see how their high CRI affects PAR. In terms of the L/w printed on the box, they don't look like winners. But, maybe that has something to do with CRI (which is somehow related to the sun's spectral balance, I've read).

I'm thinking the newer plastic-enclosed PAR-38 (and 30, and 20) will be winners. It looks like the lens can be removed easily. If it doesn't pop off, the lip around the edge would serve as a guide for a hacksaw. Since they come in their own reflector, that makes them easier to get started with than lightbulbs (which need a separate reflector to get the most out of them. The separate reflectors are generic, not matched to the bulb.).

I'm noticing a trend with LED lightbulbs to go back to frosted glass (like old incandescents). I think the LEDs are suspended like filaments. That's a step backwards for growing. You get more light from the base mounted LEDs (all pointing the same direction). If that becomes the lightbulb standard, the PAR-xx (and maybe BR30) floodlights will be the only solution.

I made this grid today:

I drew 1" circles to help me easily/consistently position the probe. I'm still unclear if 8/16" with 12" high light will be the right scale for these lightbulbs. Or, if it will work with both lightbulbs and floodlights. I'll find out soon.

Do you ever calibrate your PAR meter using noon-time sun, the way the manual describes? I wanted to check mine before getting too deep into measuring lightbulbs. But, there's more more moisture in the air lately, high clouds. It doesn't seem like optimal sunny days.

 

[LEDTonic]

Not yet.

I bought some bulbs today. I got two Cree lightbulbs. I'm curious to see how their high CRI affects PAR. In terms of the L/w printed on the box, they don't look like winners. But, maybe that has something to do with CRI (which is somehow related to the sun's spectral balance, I've read).

I'm thinking the newer plastic-enclosed PAR-38 (and 30, and 20) will be winners. It looks like the lens can be removed easily. If it doesn't pop off, the lip around the edge would serve as a guide for a hacksaw. Since they come in their own reflector, that makes them easier to get started with than lightbulbs (which need a separate reflector to get the most out of them. The separate reflectors are generic, not matched to the bulb.).

I'm noticing a trend with LED lightbulbs to go back to frosted glass (like old incandescents). I think the LEDs are suspended like filaments. That's a step backwards for growing. You get more light from the base mounted LEDs (all pointing the same direction). If that becomes the lightbulb standard, the PAR-xx (and maybe BR30) floodlights will be the only solution.

I made this grid today:

View attachment 883516

I drew 1" circles to help me easily/consistently position the probe. I'm still unclear if 8/16" with 12" high light will be the right scale for these lightbulbs. Or, if it will work with both lightbulbs and floodlights. I'll find out soon.

Do you ever calibrate your PAR meter using noon-time sun, the way the manual describes? I wanted to check mine before getting too deep into measuring lightbulbs. But, there's more more moisture in the air lately, high clouds. It doesn't seem like optimal sunny days.

I haven't. Actually, I don't recall getting a manual.
I just searched online and did find Direct link to PDF MQ-500 (<<link).
Although it had nothing in it that indicated that I should calibrate it myself, or how to do so.
Could you snap a photo or two of that information?

 

[LEDTonic]

But, maybe that has something to do with CRI (which is somehow related to the sun's spectral balance, I've read).

"The CRI is calculated by comparing the color rendering of the test source to that of a "perfect" source, which is a black body radiator for sources with correlated color temperatures under 5000 K, and a phase of daylight otherwise (e.g., D65). " -wiki
"CRI merely measures the faithfulness of any illuminant to an ideal source with the same CCT, but the ideal source itself may not render colors well if it has an extreme color temperature, due to a lack of energy at either short or long wavelengths "
"6500 K is chosen for reference since it has a relatively even distribution of energy over the visible spectrum and hence high gamut area. "

Indeed, sunlight is very close to the 6000k black body line (being 6500k and having a peak, slightly more blue)
But for the bulbs we are measuring, being 2700k (my bulbs) and your bulbs (kelvin?) the comparison is done differently and can't be compared to the light from our sun?

I've cut and copied the CRI 70, 80 and, 90-graphs of Samsung lm301b at 3500k and made a reference line at 600nm. I took this diode as an example because its data and specifications are easily available.

Yes, red wavelengths promote flowering, but is the PPFD (or even YPFD) increased or decreased?
At 70&80 CRI 3500k top bin VS 90 CRI 3500k top bin, the difference is 38-40lm VS 32-34lm (according to Samsung)
Final lm/w is affected by many factors such as driver efficiency, diode brand, diode size, and thermal management, but the CRI absolutely plays a big part.
Are we sure that a high CRI directly translates to a superior light for growing, when everything is accounted for?
While the quality of light has an impact on plants and photosynthesis, so does the quantity of light.
Somewhere, there is a crossing point where purchase price and efficacy will win over spectral "perfection", I think.

Whoops, I sidetracked a little. Oh well.
What is the CRI on the bulbs that you bought? I'd guess that 80 is the most common, overall.

 

[az2000]

I just searched online and did find Direct link to PDF MQ-500 (<<link).
Although it had nothing in it that indicated that I should calibrate it myself, or how to do so.
Could you snap a photo or two of that information?

It's on page 15 of that manual (my meter didn't come with a manual either. I found it online too.). It involves going to a website and finding out the umoles which should fall on your location (lat/long), at a specific elevation, on a specific day, at a specific time. You're suppose to do this occasionally and if the numbers consistently don't match, then make arrangements to have it calibrated at the factory.

I'd like to have a baseline for mine before getting too far into measuring things. But, my local conditions aren't favorable right now.

BTW: I measured some bulbs last night. I realized I got carried away drawing circles on my grid. I'm not measuring that many spots around the perimeter. Only the corners and halfway between.

 

[LEDTonic]

It's on page 15 of that manual (my meter didn't come with a manual either. I found it online too.). It involves going to a website and finding out the umoles which should fall on your location (lat/long), at a specific elevation, on a specific day, at a specific time. You're suppose to do this occasionally and if the numbers consistently don't match, then make arrangements to have it calibrated at the factory.

I'd like to have a baseline for mine before getting too far into measuring things. But, my local conditions aren't favorable right now.

BTW: I measured some bulbs last night. I realized I got carried away drawing circles on my grid. I'm not measuring that many spots around the perimeter. Only the corners and halfway between.

Wow, what an amazing tool that is (calibration website)
I did measure the sun's PPFD which I wrote a short blog about. Comparing to those numbers at 13.10, My sensor is around 5%+, but when all the reflective surroundings are accounted for, I'd guess the value is close to 0%. Open window with white window frames, balcony handrails, etc. I'm sure it all adds up to a fair bit.
As you can see the readings are a bit jumpy later in the afternoon (in the blog post) and this is because of surrounding trees etc, as I had to move outdoors because of shadows. I will definitely check again soon in a more controlled situation to confirm. Thanks for the tip!

It's easy to get a little carried away. Although I want to say that too many circles are preferred over too few. Again, depending on what your goal is with your final product. Twice as many measurements don't take twice the time, compared to hanging each lamp again at an exact height and re-do everything (which I have, more than once).
Btw, I film myself when I am measuring and saying the measurements out loud. Afterwards, I listen to the recording and type all measurements in a spreadsheet. And if there suddenly is one measurement that doesn't feel right, I can re-watch the video and see if I missed a spot or if something else happened such as accidentally pulling a cable and moving the lamp slightly (example). A lot can go wrong when you measure 81 points at five heights, with three different light settings at each heigh (veg, bloom, veg+bloom)

 

[az2000]

I tested a GE "Basic LED" ligtbulb (9.5w 60w-equiv, warm and cool). It's their cheap line of bulbs (not dimmable. No CRI mentioned.). I think GE makes it exclusively for Lowes. I don't see anyone else selling it.

I attached an example PDF showing how I'm planning to memorialize the test results (you have to look hard for it. This forum's theme doesn't make links and things stand out well). This is the only one I have, so I can't summarize anything about it. Eventually I'll put this on my Google Drive with other results. I'll have a summary PDF (rank the test results, and link to each test-result PDF). I need to do some more and see how it goes together. (I need to baseline a CFL too. It surprises me how people still hang unreflected CFLs in the air. Comparing a globeless LED lightbulb to one of those is attention-getting. It's like 4x the light for 33% less electricity. It's enormous. At least when I measured lumens.).

When I measured lumens, I was just looking for the brightest light per watt. It will be interesting if any lightbulbs stand out as better in terms of PAR. Getting back to CRI, if you watched one of those DIY spectrometer videos, the guy illustrated how "white" on a computer screen is really just red, green & blue. He points his tube-meter white screen and it's just 3 spikes. It's not a nice blend of the entire spectrum from blue to red.

I wonder if CRI has something to do with that. Maybe that kind of "white" has low CRI because it's such a lousy match to the full spectrum of the sun? And, the higher the CRI, the more complete. If true, then maybe that would be reflected in PAR? (I should try to measure the PPFD of my laptop screen. ha. And the lumens. If there's a big difference, that might mean something.).