I'm a Metrologist witch is Calibration and repair of instrumentation. You did a fine job. I used a bulb that was calibrated at NIST for just the same type calibrations. Good job.

To find equal lumen value between two incandescent bulbs without having a meter you take a piece of tracing paper or what we call onion skin paper. Place one drop of mineral oil on it. Slide the paper between the two lite bulbs and you will notice the stain will stand out. Adjust the voltage of one of the bulbs until the stain disappears and you will now have equal lumen values. I learned this online from an Old Timer and was fascinated by the simple theory.

I searched high and low, you are the only person that answered all my questions. I just got a par meter today and was wondering light distance from light source to my meter. 11 inches. I figured 12 so I was close. Ty so much

Excellent coverage of the subject, making it easy for all to understand. Thanks!

Alhamdulillah,this is what i've looking for to complete my thesis,thanks a lot,i've got your point😍

Picked up a lux meter at a garage sale ages ago. Need to use it tonight. This video shall help. Thanks

Really enjoyed that video. Very well explained in plain english. Thank you very much

I use a similar meter to get the light even on a photographic copy stand. The sensitivity of these meters to slight differences makes it quite precise in this application. I also use it to get a sense of the brightness range for studio lighting. Nice to see some math deployed in checking out the claims on light bulbs.

Been looking for some filament led bulbs from a store . Will give these a go. Thanks.

What an interesting exercise! I always wondered how these meters were supposed to be operated. Perhaps you might have even been closer to the box's stated Lux figure given potential mains voltage differences at your house vs the test condition(s) at the factory?

The problem is that people think of Lumen/Lux considering a "flat" surface to illuminate (which of course is the real life situation) so radiation fall off is of course different when considering right under the lamp or at the edge of a square meter. besides light intensity drops by half when light source distance is doubled. The "overlooked" parameter is in the manual (video@10 minutes) where the radiation angle is correctly defined as 4pi sterradians which is far from a "flat surface" JFWIW

I liked the somewhat shocked "I don't need to close the brackets..." with the calculaty-bit. Haha! It's also funny how light seems to BEAM out of the top (well, bottom...) of the light bulb as you explain about the shadowy spot. Lovely video and i don't mind it's not scientific. Still interesting.

Thx Julian. A problem I’d come across in the past and at that time concluded that I needed special equipment and a rig to achieve a meaningful measurement but your method looks straightforward and achievable. Well done that man!

Your light meter is similar to my own so it may have an adjustment feature which will allow you to calibrate it and is ideal for when there is some ambient light in your test area. Set the meter up, adjust the reading to zero and then switch on the light source under test.

Lumen: How bright a source creates it's light Lux: Brightness of the source on a certain distance

I went down the path you are on quite some time ago and ended up publishing a couple articles of "layman's guide" to understanding light and light measurement. I could probably save you and others some hair pulling as you wade into the silly jargon of illumination. The articles appeared in various US & UK amateur radio magazines in 2000. I will be glad to send you a copy or post it on my github if desired.

What about using one of these on my projector to correct the colour balance with test patterns?

I have one of these as well. What I´m most suspicious about in regards to its readings is how well it takes light color/wavelengths into account. For example it conveniently fluoresces under 400nm causing it to read much higher than it should.

cool with your lux meter, can you check to see if theres any smart phone equivalent? and if theyre actually accurate?

as far as i know lux is a effort unit and lumens are a flow unit (as volts is a effort unit and amps are a flow unit) if your meter is measuring in lux its similar to measuring the voltage, your readings vary with the distance bc you can think of your bulb like of a ball that emitts discrete beams of light and the closer to the bulb you measure the higher the desity of beams ie more lux. tldr : the measurements make sense!!! edit: looked more of the vid... glad you sort of found out your self

Never been any good at math. I was able to count may wages and my change from shopping, but square roots and bla bla bla was not needed in my daily thoughts until I watched this.Thx, nicely explained.

Did you measure the 282mm from the surface of the glass 'bulb' or from the edge of the LEDs themselves? That extra couple of mm might make all of the difference! ;)

Light has lots of units of photopic (human visible) measure. In addition to lux and lumens, there's stilbs, entendue, actuance, nits, phots, candelas, lamberts, blondels, skots, and brils. 💡💡

Thanks for sharing your experiments. I guess there are also some phone apps that might be interesting to try too.

If you can't get use an integrating sphere, you really need to study "steradians" (solid angles--you will love it!--It's like angles for a sphere rather than a triangle). Put a simple reflector around the light source as you use it here. I made a solid sphere out of wax and have ONE steradian of it sitting beside it--a cone with a spherical shaped big end that tapers to the point at the center of the sphere from which it came. Thanks for the video!!

Does this method work on directional light source (i.e floodlight)?

This was very helpful. Trying to measure the ideal distance my plants should be from a pre-determined lumen outputted system. Bought myself a lux meter thinking it would immediately translate to lumen output and of course I was wrong. Now I just need to figure out the math... ugggh, I suck at the maths. Thanks.

Correct me if I’m wrong, but is this not like trying to measure the amount of light being detected on the service area of a three-dimensional space by using the correlation of distance and a two dimensional space, that’s much smaller (a.k.a. the photodiode). The measurements would never be close to the same, right? The large 3D surface area of the sphere will always pick up a lot more light than the smaller 2D surface area of the photodiode. I’m sincerely asking, not trying to be rude. It’s been a while since I’ve had to do math so I could be off base 😂. There’s other things that we’re going to play such as how focused the the light is, the angle of the in relation to the photodiode, the distance the latest from the photodiode, ect. In my opinion you’d be better off grabbing a white trashcan or Styrofoam cooler that’s laying around the house and sticking the lux meter in there, then shining the light so it can bounce off of all the walls to get your reading. This still wouldn’t be an accurate or scientific representation of lumens but if you wanted a makeshift way to do it without having to leave the house I believe this will be the way to go. Also, I don’t think you could measure. How are you lumens using lux right? What did you use foot Candela? Again I could be completely wrong. I’d love to hear feedback.

very useful - thank you (i´ve learnt this a felt hundred years ago and now i can remember this stuff)

You could use a std incandescent bulb as a sanity check for the meter. Still what you're measuring isn't way out in left field. WAY cheaper than an integrating sphere :)

I've always wanted to know at what distance these lumen counts on the light bulb packaging was taken and now I know thank you.

Dude awesome video!

hi..i wanted to let you know that the flat green pad had caught my attention & i wanted to know what is it called because i myself will like one of those.

Best way to start out my birthday when I sit down to a fresh posted video from you. Thanks mate, keep being awesome.

Can I use this device to measure solar radiation? Please

Nice effort.

It's easy to build an integrating sphere, it doesn't have to be spherical or highly reflective, a white box will do, but it does need to be calibrated with a known source of light. If you're not fussy you can use a 60W incandescent bulb as the reference and then just use that as your unit of brightness.

It's 2:00AM, I just finished editing my latest video, waiting for it to render. Julian, you're keeping me alive.

You cant necessarily base lightbulb comparison solely on lux. When it comes to reflector design, the biggest factor is the size of the light source. The light emission of the filament bulb happens on a much smaller surface area than some led bulbs. The reflectors in cars are designed to take advantave of this. Using led replacements with large emission areas and high claimed light output may actually yield terrible results, as the reflectors arent optimized for the larger emission area. In fact you may find that led replacements with lower lumens but emited from a single source on two or 3 sides will yield better results than a replacement with 10 xhp70 chips, that may melt the housing from all the heat :) In addition if you have 16 1 watt chips on a single led bulb replacing a 10w incandescent... well... do the math

Very nice video

Julian, PLEASE Do The LED Light Bulb Kit! Build It!!!

Briliant! 👍

You are only looking at about a 2% error or so, that's pretty good

Useful video

I dont even know why i like this. But this was dope. And you used the metric system which was refreshing. where you from sir ?

Good trying experiment!

That likely isn't you only lux meter: your phone probably has one, and those are surprisingly accurate. Find an app that will show the reading and then you have something to compare with!

Thanks, I made mistakes of what distance it was, thought 1 metre was the distance... oh well, new everyday.

As you indicated, your calculation would only be meaningful if the output of the lamp was isotropic, which it clearly isn't. Another issue could be that devices are often calibrated against a known illuminant, such as tungsten filament lamp, and that will have a very different colour spectrum compared to your LED lamp. I touch on this subject a little at work and ended up making myself a little cheat sheet to help me picture the relationship between the different radiometric and photometric terms.

Measuring lumens by estimating it from one point is often very inaccurate. Light can have different intensity to different directions! It is usually measured by something like a diffusing sphere that makes the light level even and you can estimate total amount of light from one point. Led lights often have lenses built in and are more or less directional. The problem is easy to see if you take a directional light like a flashlight. It has very different output at the edge of the light cone than in the center spot. (And a lot more different if you measure it from the side or back.)

Lux is a calculation of Lumens projected over a known area (as is foot candles). 1 Lux = 1 Lumen X 1 meter X 1 meter. If this device doesn't know what your distance is from the light source or the area of the surface it projects on, how can it measure Lux or Foot Candles? This is a Lumen meter. When the manufacturer doesn't know the difference, I don't trust the output it produces.

This is the most scientific video I've seen lately, excluding Cody's Lab ones.

*How to measure nits of a screen? (cd/m2)*

Hello. Good thinking, but....this 0.282 is the diameter and not the radius......with whatever that might mean.! Good job

The professional lab tool is called an Integrating sphere. It is the Only way to get accurate readings of what is described on the box or from a spec sheet. Lux and lumen are okay if all you need to do is measure visible spectrum rudimentary. Not to mention those testers are veeeery innacurate eveen in testing what they are designed for. Apogee instruments even though they are expensive. Light is serious business.

How about comparing the led lamp with an old school 60w incandescent.

And what if I have a bulb with Lux units on the package ... What's the correct way to measure Luxes with this Uni-T unit ? BTW immersive video and science.

So if you want to measure lumens from sun light how you do it?

thank you

does this device work on candle light 🕯 🤔

Hi Julian, since you have used the formula for the surface area of a (perfect) sphere and in your experiment if we ignore any actual bulb differences from an ideal sphere (plus spurious reflectivities etc) you will however still be a factor of around 2X in error because the light meter does not look at the entire spherical surface of the bulb but instead looks only at the surface of half a sphere (the maximum surface area presented to the meter at any one time), since the meter cannot look at the back and front of the bulb surface both at the same time. And yes you are quite correct about the cost of the meter being very expensive at around AUD$560.00! Interesting experiment nevertheless. Cheers from Down Under

Sr is a 2D angle of one radian per one radian.

9:38 the best part :D

i need a oscilloscope, I’m wondering if a microphone could be used as a battery to light a led when a noise is detected 🤔😔

This will only be true if 1. The light bulb radiates light equally in all direction 2. The light bulb can shine the whole surface area of a sphere (equally), including the bottom part of the bulb. (Assume bulb is in the center of sphere) 3. This is done in a dark room/black room. 1 and 2 will make lumen and candela equal in magnitude. No trouble in getting the solid angle. 3 will make the measurement accurate. Note that the reflectance will affect the measurement even if there are no other light source during the measurement.

Area=4⋅π⋅R2 area of a sphere should be in the description.

28.2cm or 11.10” or 11” 3.5/32” to determine Lux

Im against using Wikipedia as a source for actual fact. But regardless this has been very illuminating for me cheers

The problem with LED replacements for automotive signal lamps is the reflector is designed to work with a specific filament location.

What's a foot candle 🕯️

I think the measurement is right because the meter has a tolerance level around 3%

282mm is the radius, which extends halfway into the bulb. You need 282mm minus the bulb radius.

You can get a PS sphere or a white PVC pipe and accessories and make your own integrating sphere, into which you can put your DUT (in this case the light bulb) and the lux meter, and using a simple calculation you can get the lumens. See this: kzfaq.info/get/bejne/rrV1ZNycr5u7cYk.html.

What is FC?

You can measure lux using your Android phone if you have auto brightness in your brightness display setting Just install CPUz and click on sensors tab Boom You got another lux measurement device

at 282 mm radius, the circumference is 1. 77 meter.

6 watts won't get you 800 lumens (60 watts) from an LED, more like 300-400 lumens from an LED, depending on color temp and efficiency.

That was a good explanation. Measuring light intensity is fucked up. Too many units. Also, light meters ( at least cheaper ones

the inverse square law of illumination.

Wouldn't it be easier with a white pipe?

9:42 radian in 3D =? pixel - > voxel radian - > steradian 2D - > 3D 😎

You don't need completely dark room if you can zero the reading, well you can't with this matter :/

i hate led lamps, they look extremely bright when directly looking into them but the room is still dark.

Clarified :)

I need this

This is all so confusing..

Fork handles Or four candles ? 😂

Your formula for calculating the area of a circle is incorrect. It should be "A=πr2". It is not "A=4πr2". Not sure why I managed to remember a formula from my school days of about 4 decades ago, a formula that I hardly ever need to use, but there you have it.

retest incand bulb ,, huh

Stop saying is not scientific, it really is, although not very precise. :) Additionally, the assumption under the 28.2cm is that the source of light is a point of size 0, so you should take into account the size of the bulb.

science

1 JOHN 1:5 This is the message we have heard from Him and announce to you, that *God is Light* ,and in Him there is no darkness at all.

π×🎥²=💤 Lol

BULBS GO IN THE GROUND TO GROW FLOWERS...THAT IS A LAMP

So the conclusion is this meter is useless because you won't get a good condition to measure it😀😀😀

Don't you have a basement?

2:24 taking print outs = wasting paper