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Compile and install Digikam on Ubuntu 20.04 Focal

Friday, March 26, 2021 

Digikam is an incredibly powerful media management tool that integrates a great collection of powerful media processing projects into a single, fairly nice and moderately intuitive user interface. The problem is that it make use of SO many projects and libraries that installation is quite fragile and most distributions are many years out of date – that is a typical sudo apt install digikam will yield version 4.5 while release is (as of this writing) 7.2.

In particular, this newer version has face detection that runs LOCALLY – not on Google or Facebook’s servers – meaning you don’t have to trade your personal photos and all the data implicit in them to a data broker to make use of such a useful tool.  Sure, Google once bought and then improved Picasa Desktop which gave you this function, but then they realized this was cutting into their data harvesting business and discontinued Picasa and tried to convince people to let them look at all their pictures with Google Photos.  We really, really need to make personal data a toxic asset, such an intolerable liability that any company that holds any personal data has negative value.  But until then, use FOSS software on your own hardware where ever possible.

You can compile the latest version on Ubuntu 20.04 Focal Fossa, though not exactly painlessly, or you can install the flatpak easily. I hate flatpaks with a passion, so I went through the exercise and found what appears to be stable success with the following procedure which yielded a fully featured digikam with zero dependency errors or warnings and all features enabled using MariaDB as a backend.

Install and configure MariaDB

sudo apt update
sudo apt install mariadb-server
sudo mysql_secure_installation

The secure options are all good, accept them unless you know better.

Start the server (if it isn’t)

sudo systemctl start mariadb.service
sudo systemctl enable mariadb --now
sudo systemctl status mariadb.service

Do some really basic config:

sudo nano /etc/mysql/mariadb.conf.d/50-server.cnf

and set:

character-set-server = utf8mb4
collation-server = utf8mb4_general_ci
default_storage_engine = InnoDB

Switch to mariadb and create an admin user account and (I’d suggest) one for digikam.  It seems this has to be done before the first connect and can’t be fixed after.  You’ll probably want to use a different ‘user’ than I did, but feel free.

sudo mariadb
CREATE USER 'gessel'@'localhost' IDENTIFIED BY 'password';
GRANT ALL ON *.* TO 'gessel'@'localhost' IDENTIFIED BY 'password';
CREATE DATABASE digikam;
GRANT ALL PRIVILEGES ON digikam.* TO 'gessel'@'localhost';
FLUSH PRIVILEGES;

should correctly create the correct user – though check the instructions tab on the database connection options pane for any changes if you’re following these instructions for install of a later version. You will need the socket location to connect to the database so before exit; run:

mysqladmin -u admin -p version

Should yield something like:

Enter password: 
mysqladmin  Ver 9.1 Distrib 10.3.25-MariaDB, for debian-linux-gnu on x86_64
Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others.

Server version		10.3.25-MariaDB-0ubuntu0.20.04.1
Protocol version	10
Connection		Localhost via UNIX socket
UNIX socket		/var/run/mysqld/mysqld.sock
Uptime:			5 hours 26 min 6 sec

Threads: 29  Questions: 6322899  Slow queries: 0  Opens: 108  Flush tables: 1  Open tables: 74  Queries per second avg: 323.157

And note the value for UNIX socket, you’re going to need that later: /var/run/mysqld/mysqld.sock – yours might vary.

Install digiKam Dependencies

Digikam has just a few dependencies.just a few... the below command should install the needed for 7.20 on Ubuntu 20.04. Any other version combination might be different.:

sudo aptitude install \
bison \
checkinstall \
devscripts \
doxygen \
extra-cmake-modules \
ffmpeg \
ffmpegthumbnailer \
flex \
graphviz \
help2man \
jasper \
libavcodec-dev \
libavdevice-dev \
libavfilter-dev \
libavformat-dev \
libavutil-dev \
libboost-dev \
libboost-graph-dev \
libeigen3-dev \
libexiv2-dev \
libgphoto2-dev \
libjasper-dev \
libjasper-runtime \
libjasper4 \
libjpeg-dev \
libkf5akonadicontact-dev \
libkf5calendarcore-dev \
libkf5contacts-dev \
libkf5doctools-dev \
libkf5filemetadata-dev \
libkf5kipi-dev \
libkf5notifications-dev \
libkf5notifyconfig-dev \
libkf5sane-dev \
libkf5solid-dev \
libkf5threadweaver-dev \
libkf5xmlgui-dev \
liblcms2-dev \
liblensfun-dev \
liblqr-1-0-dev \
libmagick++-6.q16-dev \
libmagick++-6.q16hdri-dev \
libmagickcore-dev \
libmarble-dev \
libqt5opengl5-dev \
libqt5sql5-mysql \
libqt5svg5-dev \
libqt5webkit5-dev \
libqt5webview5 \
libqt5webview5-dev \
libqt5x11extras5-dev \
libqt5xmlpatterns5-dev \
libqtav-dev \
libqtwebkit-dev \
libswscale-dev \
libtiff-dev \
libusb-1.0-0-dev \
libx264-160 \
libx264-dev \
libx265-192 \
libx265-dev \
libxml2-dev \
libxslt1-dev \
marble \
pkg-kde-tools \
qtbase5-dev \
qtbase5-dev-tools \
qtmultimedia5-dev \
qtwebengine5-dev \
qtwebengine5-dev-tools

Compile Digikam

Switch to your projects directory (~/projects, say) and get the source tarball and cross your fingers and go to town. The make -j4 command will take a while to compile everything.

wget https://download.kde.org/stable/digikam/7.2.0/digikam-7.2.0.tar.xz
tar -xvf digikam-7.2.0.tar.xz
cd digikam-7.2.0.tar.xz
mkdir build
./bootstrap.linux
cd build
make -j4
su
make install/fast

the ./bootstrap.linux result should be as below – if it indicates a something is missing, then double check dependencies.  If you’ve never compiled anything before, you might need to install cmake and and some other basics:

-- ----------------------------------------------------------------------------------
--  digiKam 7.2.0 dependencies results   <https://www.digikam.org>
-- 
--  MySQL Database Support will be compiled.. YES (optional)
--  MySQL Internal Support will be compiled.. YES (optional)
--  DBUS Support will be compiled............ YES (optional)
--  App. Style Support will be compiled...... YES (optional)
--  QWebEngine Support will be compiled...... YES (optional)
--  libboostgraph found...................... YES
--  libexiv2 found........................... YES
--  libexpat found........................... YES
--  libjpeg found............................ YES
--  libkde found............................. YES
--  liblcms found............................ YES
--  libopencv found.......................... YES
--  libpng found............................. YES
--  libpthread found......................... YES
--  libqt found.............................. YES
--  libtiff found............................ YES
--  bison found.............................. YES (optional)
--  doxygen found............................ YES (optional)
--  ccache found............................. YES (optional)
--  flex found............................... YES (optional)
--  libakonadicontact found.................. YES (optional)
--  libmagick++ found........................ YES (optional)
--  libeigen3 found.......................... YES (optional)
--  libgphoto2 found......................... YES (optional)
--  libjasper found.......................... YES (optional)
--  libkcalendarcore found................... YES (optional)
--  libkfilemetadata found................... YES (optional)
--  libkiconthemes found..................... YES (optional)
--  libkio found............................. YES (optional)
--  libknotifications found.................. YES (optional)
--  libknotifyconfig found................... YES (optional)
--  libksane found........................... YES (optional)
--  liblensfun found......................... YES (optional)
--  liblqr-1 found........................... YES (optional)
--  libmarble found.......................... YES (optional)
--  libqtav found............................ YES (optional)
--  libthreadweaver found.................... YES (optional)
--  libxml2 found............................ YES (optional)
--  libxslt found............................ YES (optional)
--  libx265 found............................ YES (optional)
--  OpenGL found............................. YES (optional)
--  libqtxmlpatterns found................... YES (optional)
--  digiKam can be compiled.................. YES
-- ----------------------------------------------------------------------------------

Launch and configure Digikam

The Configuration options are pretty basic, but note that to configure the Digikam back end you’ll need to use that MariaDB socket value you got before and the user you created like so UNIX_SOCKET=/var/run/mysqld/mysqld.sock:

 

On the first run, it will download about 350mb of code for the face recognition engine.  Hey – maybe a bit heavy, but you’re not giving the Google or Apple free lookie looks at all your personal pictures.  Also, if all this is a bit much (and, Frankly, it is) I’d consider Digikam one of the few applications that makes the whole flatpak thing seem somewhat justified.  Maybe.

Some advice on tuning:

I recommend mysqltuner highly, then maybe check this out (or just leave it default, default works well).

Tuning a database is application and computer specific, there’s no one size fits any, certainly not all, and it may change as your database grows. There are far more expert and complete tuning guides available, but here’s what I do:

Pre-Tuning Data Collection

Tuning at the most basic involves instrumenting the database to log problems, running it for a while, then parsing the performance logs for useful hints. The mysqltuner.pl script is far more expert at than I’ll ever be, so I pretty much just trust it. You have to modify your mysqld.cnf file to enable performance data collection (which, BTW, slows down operation, so undo this later) which for MariaDB means adding a few lines:

sudo nano /etc/mysql/mariadb.conf.d/50-server.cnf
# enable performance schema to allow optimization, but ironically hit performance, so disable after tuning.
# in the [mysqld] section insert
performance_schema=ON
performance-schema-instrument='stage/%=ON'
performance-schema-consumer-events-stages-current=ON
performance-schema-consumer-events-stages-history=ON
performance-schema-consumer-events-stages-history-long=ON

Follow the instructions for installing mysqltuner.pl at https://github.com/major/MySQLTuner-perl#downloadinstallation

I rather like this guide’s helpful instructions for putting the script in /usr/local/sbin/ so it is in the execution path:

sudo wget https://raw.githubusercontent.com/major/MySQLTuner-perl/master/mysqltuner.pl -O /usr/local/sbin/mysqltuner.pl
sudo chmod 700 /usr/local/sbin/mysqltuner.pl
sudo mysqltuner.pl

Then restart with sudo service mariadb restart then go about your business with digikam – make sure you rack up some real hours to gather useful data on your performance. Things like ingesting a large collection should generate useful data. I’d suggest doing disk tuning first because that’s hardware not load dependent.

Disk tuning

Databases tend to hammer storage and SSDs, especially SLC/enterprise SSDs, massively improve DB performance over spinning disks – unless you have a massive array of really good ones. I’m running this DB on one spinning disk, so performance is very MEH. MySQL and MariaDB make some assumptions about disk performance which is used to scale some pretty important parameters for write caching. You can meaningfully improve on the defaults by testing your disk with a great linux utility called “fio”.

sudo apt install fio
fio --randrepeat=1 --ioengine=libaio --direct=1 --gtod_reduce=1 --name=test --filename=test --bs=4k --iodepth=64 --size=4G --readwrite=randrw --rwmixread=75

This will take a while and will give some very detailed information about the performance of your disk subsystem, the key parameters being average and max write IOPS. I typically create a # performance tuning section at the end of my [mysqld] section and before [embedded] and I’ll put these values in as, say: (your IOPS values will be different):

# performance tuning

innodb_io_capacity              = 170
innodb_io_capacity_max          = 286

and sudo service mariadb restart

Using mysqltuner.pl

After you’ve collected some data, there may be a list of tuning options.

sudo nano /etc/mysql/mariadb.conf.d/50-server.cnf

Mine currently look like this, but they’ll change as the database stabilizes and my usage patterns change.

# performance tuning

innodb_io_capacity              = 170
innodb_io_capacity_max          = 286

innodb_stats_on_metadata        = 0
innodb_buffer_pool_size         = 4G
innodb_log_file_size            = 512M
innodb_buffer_pool_instances    = 4
skip_name_resolve               = 1
query_cache_size                = 0
query_cache_type                = 0
query_cache_limit               = 2M
max_connections                 = 175
join_buffer_size                = 4M
tmp_table_size                  = 24M
max_heap_table_size             = 24M
innodb_buffer_pool_size         = 4G
max_allowed_packet              = 128M

and

sudo service mariadb restart

Note max_allowed_packet = 128M comes from this guide. I trust it, but it isn’t a mysqltuner suggestion.

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Category: HowToLinuxphotoPositivereviewstechnology

WebP and SVG

Tuesday, September 1, 2020 

Using WebP coded images inside SVG containers works.  I haven’t found any automatic way to do it, but it is easy enough manually and results in very efficiently coded images that work well on the internets.  The manual process is to Base64 encode the WebP image and then open the .svg file in a text editor and replace the

xlink:href="data:image/png;base64, ..."

with

xlink:href="data:image/webp;base64,..."

(“…” means the appropriate data, obviously).


Back in about 2010 Google released the spec for WebP, an image compression format that provides a roughly 2-4x coding efficiency over the venerable JPEG (vintage 1974), derived from the VP8 CODEC they bought from ON2. VP8 is a contemporary of and technical equivalent to H.264 and was developed during a rush of innovation to replace the aging MPEG-II standard that included Theora and Dirac. Both VP8 and H.264 CODECs are encumbered by patents, but Google granted an irrevocable license to all patents, making it “open,” while H.264s patents compel licensing from MPEG-LA.  One would think this would tend to make VP8 (and the WEBM container) a global standard, but Apple refused to give Google the win and there’s still no native support in Apple products.

A small aside on video and still coding techniques.

All modern “lossy” (throwing some data away like .mp3, as opposed to “lossless” meaning the original can be reconstructed exactly, as in .flac) CODECs are founded on either Discrete Cosine Transform (DCT) or Wavelet (DWT) encoding of “blocks” of image data.  There are far more detailed write ups online that explain the process in detail, but the basic concept is to divide an image into small tiles of data then apply a mathematical function that converts that data into a form which sorts the information from least human-perceptible to most human-perceptible and sets some threshold for throwing away the least important data while leaving the bits that are most important to human perception.

Wavelets are promising, but never really took off, as in JPEG2000 and Dirac (which was developed by the BBC).  It is a fairly safe bet that any video or still image you see is DCT coded thanks to Nasir Ahmed, T. Natarajan and K. R. Rao.  The differences between 1993’s MPEG-1 and 2013’s H.265 are largely around how the data that is perceptually important is encoded in each still (intra-frame coding) and some very important innovations in inter-frame coding that aren’t relevant to still images.

It is the application of these clever intra-frame perceptual data compression techniques that is most relevant to the coding efficiency difference between JPEG and WebP.

Back to the good stuff…

Way back in 2010 Google experimented with the VP8 intra-coding techniques to develop WebP, a still image CODEC that had to have two core features:

  • better coding efficiency than JPEG,
  • ability to handle transparency like .png or .tiff.

This could be the one standard image coding technique to rule them all – from icons to gigapixel images, all the necessary features and many times better coding efficiency than the rest.  Who wouldn’t love that?

Apple.

Of course it was Apple.  Can’t let Google have the win.  But, finally, with Safari 14 (June 22, 2020 – a decade late!) iOS users can finally see WebP images and websites don’t need crazy auto-detect 1974 tech substitution tricks.  Good job Apple!

It may not be a coincidence that Apple has just released their own still image format based on the intra-frame coding magic of H.265, .heif and maybe they thought it might be a good idea to suddenly pretend to be an open player rather than a walled-garden-screw-you lest iOS insta-users wall themselves off from the 90% of the world that isn’t willing to pay double to pose with a fashionable icon in their hands.  Not surprisingly, .heic, based on H.265 developments is meaningfully more efficient than WebP based on VP8/H.264 era techniques, but as it took WebP 10 years to become a usable web standard, I wouldn’t count on .heic  having universal support soon.

Oh well.  In the mean time, VP8 gave way to VP9 then to VP10, which has now AV1, arguably a generation ahead of HEVC/H.265.  There’s no hardware decode (yet, as of end of 2020) but all the big players are behind it, so I expect 2021 devices will and GPU decode will come in 2021. By then, expect VVC (H.266) to be replacing HEVC (H.265) with a ~35% coding efficiency improvement. 

Along with AV1’s intra/inter-frame coding advance, the intra-frame techniques are useful for a still format called AVIF, basically AVIF is to AV1 (“VP11”) what WEBP is to VP8 and HEIF is to HEVC. So far (Dec 2020) only Chrome and Opera support AVIF images.

Then, of course, there’s JPEG XL on the way.  For now, the most broadly supported post-JPEG image codec is WEBP.

SVG support in browsers is a much older thing – Apple embraced it early (SVG was not developed by Google so….) and basically everything but IE has full support (IE…  the tool you use to download a real browser).  So if we have SVG and WebP, why not both together?

Oddly I can’t find support for this in any of the tools I use, but as noted at the open, it is pretty easy.  The workflow I use is to:

  • generate a graphic in GIMP or Photoshop or whatever and save as .png or .jpg as appropriate to the image content with little compression (high image quality)
  • Combine that with graphics in Inkscape.
  • If the graphics include type, convert the type to SVG paths to avoid font availability problems or having to download a font file before rendering the text or having it render randomly.
  • Save the file (as .svg, the native format of Inkscape)
  • Convert the image file to WebP with a reasonable tool like Nomacs or Ifranview.
  • Base64 encode the image file, either with base64 # base64 infile.webp > outfile.webp.b64 or with this convenient site
  • If you use the command line option the prefix to the data is “data:image/webp;base64,
  • Replace the … on the appropriate xlink:href="...." with the new data using a text editor like Atom.
  • Drop the file on a browser page to see if it works.

WordPress blocks .svg uploads without a plugin, so you need one

The picture is 101.9kB and tolerates zoom quite well. (give it a try, click and zoom on the image).

 

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Posted at 08:54:16 GMT-0700

Category: HowToLinuxphotoself-publishingtechnology

Dealing with Apple Branded HEIF .HEIC files on Linux

Saturday, August 22, 2020 

Some of the coding tricks in H.265 have been incorporated into MPEG-H coding, an ISO standard introduced in 2017, which yields a roughly 2:1 coding efficiency gain over the venerable JPEG, which was introduced in 1992.  Remember that?  I do; I’m old.  I remember having a hardware NUBUS JPEG decoder card.   One of the reasons JPEG has lasted so long is that images have become a small storage burden (compared to 4k video, say) and that changing format standards is extremely annoying to everyone.

Apple has elected to make every rational person’s life difficult and put a little barbed wire around their high-fashion walled garden and do something a little special with their brand of a HEVC (h.265) profile for images.  Now normally seeing iOS user’s insta images of how fashionable they are isn’t really worth the effort, but now and then a useful correspondent joins the cult and forks over a ton of money to show off a logo and starts sending you stuff in their special proprietary format.  Annoying, but fixable.

Assuming you’re using an OS that is neither primarily spyware nor fashion forward, such as Linux Mint, you can install HEIF decode (including Apple Brand HEIC) with a few simple commands:

$ sudo add-apt-repository ppa:jakar/qt-heif
$ sudo apt update
$ sudo apt install qt-heif-image-plugin

Once installed, various image viewers should be able to decode the images.  I rather like nomacs as a fairly tolerable replacement for Irfan Skiljan‘s still awesome irfanview.

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Posted at 03:56:36 GMT-0700

Category: HowToLinuxphotoPositivereviewstechnology

1976 GMC Suburban

Friday, May 17, 2019 

When I was a young child, my dad bought a brand new 1976 GMC Suburban. Yellow. No extras at all – no head liner, plastic seats, manual everything, 305 V8.

It became my car in high school, survived that. Came out to California with me; ended up in the service of SRL, survived that too.

Eventually, it escaped.

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Posted at 13:18:33 GMT-0700

Category: photoSRL

Green Lacewings

Sunday, January 10, 2016 

I noticed that my avocado tree was developing brown spots on the leaves, which were almost certainly the result of Persea mites.

Leaf Symptoms

 

So I looked up some possible cures, and it seemed like introducing a predator would be the best option and the least hassle.  I’d had good luck with introduced ladybugs a few years back, which formed a stable population that survived for many years after introduction.  For this pest, green lacewings are recommended.  I found a nearby insectary that could provide larvae on cards and they shipped them overnight.

Green Lacewing egg cards

 

 

The little guys look cute just waiting to hatch…

Green Lacewing Eggs

 

I hung he cards on the leaves of the tree after incubating them overnight in a warm room, and they should hatch sometime in the next day or two, as long as the ants don’t find them first…

Card in tree

 


Update 8 Sept 2016:

The green lacewings seem to have eaten all the mites.  It has been 9 months and there aren’t any signs of damage to this spring’s leaves.  Yay!

No mite bites

The new leaves that grew seem to be developing without any bites at all.  The old leaves that were too damaged have fallen off, but the surviving older leaves still show the scars of the mites.  Green lacewings seem to have done the trick.

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Posted at 14:40:47 GMT-0700

Category: photoPositivereviews

United’s Magic Trays

Thursday, September 3, 2015 

@United has new coach trays that are coated with a material that has an amazing coefficient of friction.  They are not sticky at all—there’s no adhesion effect—it is all friction.  Even low surface energy plastics don’t slide on it at all.

The approximately 75-80° angle in the picture is the point at which the cup topples over itself.  It isn’t adhered to the surface and it doesn’t appear to slide at all before toppling.

Super Friction Tray

This would be the perfect coating for a smart phone pad in a car.

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Posted at 11:00:39 GMT-0700

Category: Fabricationphotoplanestechnologytravel

Summer Blooms

Friday, July 24, 2015 

Roses Bird of Paradise Closeup Bird of Paradise Blooms Cactus Blooms

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Posted at 13:41:13 GMT-0700

Category: photoweather

Tortuga Stalking the Yard

Thursday, July 23, 2015 

Tortuga Profile

Tortuga quarter

Tortuga facing

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Category: catsphoto

The Avocado Tree is Fruiting

Tuesday, July 21, 2015 

A couple of years back a random sprout appeared in the yard. It looked like a volunteer avocado and grew bizarrely fast. After a few years, it is about 15′ tall and this year it fruited for the first time. It really is an avocado tree.
 

Avacado Tree Fruiting

 

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Category: photo

Low Voltage LED Lighting

Monday, July 13, 2015 

My kitchen has had halogen lighting for 20 years, from back when it was a slightly more efficient choice than incandescent lighting and had a pleasing, cooler (bluer, meaning the filament runs hotter) color temperature.

LEDs Installed

Progress has moved on and while fluorescent lights still have a lead in maximum luminous efficacy (lm/w), for example the GE Ecolux Watt-Miser puts out 111 lm/W, they’re less versatile than LEDs and installation is a hassle while low voltage LEDs are easy to install and look cool.

System Design

The goal of this project was to add dimmable, pleasing light to the kitchen that I found aesthetically interesting.  I wanted a decent color rendering index (CRI), ease of installation, and at reasonable cost.  I’ve always liked the look of cable lighting and the flexibility of the individual, adjustable luminaires.

I couldn’t find much information on how variable output LEDs work and what can be used to drive them.  I have a pretty good collection of high quality power supplies, which I wanted to take advantage of, but wasn’t sure if I’d be able to effectively dim the bulbs from the documentation I found. So I did some tests.

Test Configuration

I bought a few different 12V, Dimmable LEDs and set up a test configuration to verify operation and output with variable voltage and variable current.  The one bit of data I had was that using standard commercial controllers, the lowest output is typically stated to be around 70% of maximum output: that is the dimming range is pretty limited with standard (PWM/Transformer) controllers.  The results I found were much more encouraging, but revealed some quirks.

I used a laboratory-grade HP power supply with voltage and current control to drive the LEDs, decent multimeters to measure voltage and current, and an inexpensive luminance meter to measure LED output.

I measured 3 different LEDs I selected based on price and expected compatibility with the aesthetics of the project and because they looked like they’d have different internal drivers and covered a range of rated wattage.

Test Results

These bulbs have internal LED controllers that do some sort of current regulation for the diodes that results in a weird voltage/current/output response.  Each bulb has a different turn-on voltage, then responds fairly predictably to increasing input voltage with increasing output, reaches the controller stabilizing voltage and runs very inefficiently until voltage gets over the rated voltage and then becomes increasingly efficient until, presumably, at some point the controller burns out.  I find that the bulbs all run more efficiently at 14V than at the rated 12V.

As a side note, to perform the data analysis, I used the excellent xongrid plugin for excel to perform Kriging interpolation (AKA Gaussian process regression) to fit the data sets to the graphing function’s capabilities.  The graphs are generated with WP-Charts and the table with TablePress.

Watts v. Volts

This chart shows the wattage consumed by each of the three LEDs as a function of input voltage, clearly demonstrating both that the power consumption function is non-linear and that power consumption in watts improves when driven over the rated 12V.  Watts are calculated as the product of the measured Volts * Amps.  Because of the current inversion that happens as the controllers come fully on-line, these LEDs can’t be properly controlled near full brightness with a current-controlled power supply, though it works well to provide continuous and fairly linear dimming at low outputs, once the voltage/current function changes slope, the current limiting controller in the power supply freaks out.

4W LED  5W LED  7.5W LED

Lux v. Volts

This chart shows the lux output by each of the three LEDs as a function of input voltage, revealing the effect of the internal LED driver coming on line and regulating output, which complicates controlling brightness but protects the LEDs.  The 5W LEDs have a fairly gentle response slope and start a very low voltage (2V) so are a good choice for a linear power supply.  The 4W LEDs don’t begin to light up until just over 6V, and so are a good match for low-cost switch mode supplies that don’t go to zero.

4W LED  5W LED  7.5W LED

Lux/W v. Volts

This chart shows the luminous efficiency (Lux/Watt, Lumen measurement is quite complicated) by each of the three LEDs as a function of input voltage, showing that overdriving the LEDs past the rated 12V can significantly improve efficiency.  There’s some risk it will overheat the controller at some point and result in failure.  I’ll update this post if my system starts to fry LEDs, but my guess is that 14V, which cuts the power load by 20% over 12V operation with the 7.5W lamps I selected, will not significantly impact operational lifetime.

4W LED  5W LED  7.5W LED

Total System Efficiency

The emitter efficiency is relatively objective, but the total system efficiency includes the power supply.  I used a Daiwa SS-330W switching power supply I happened to have in stock to drive the system, which cost less than a dimmable transformer and matching controller, and should be significantly higher quality.  The Daiwa doesn’t seem to be easily available any more, but something like this would work well for up to 5A total load and something like this would handle as many as 40 7.5W LEDs on a single control, though the minimum 9V output has to be matched to LEDs to get satisfactory dimming. It is important not to oversize the power supply too much as switch mode supplies are only really efficient as you get close to their rated output.  An oversized switchmode power supply can be extremely inefficient.

With the Daiwa, driving 13 7.5W LEDs, I measured 8.46A at 11.94V output or 101 Watts to brightly illuminate the entire kitchen, and providing far more light than 400W of total halogen lights.  I measured the input into the power supply at 0.940A at 121.3V or 114 Watts.  That means the power supply is 88.6% efficient at 12V, which is more or less as expected for a variable output supply.

Increasing the output voltage to 14.63 Volts lowered the output current to 5.35A or 78 Watts without lowering the brightness at the installation; I measured at 168 lux at both 12.0V at 14.6V. The input current at 14.63V dropped to 0.755A or 91.6 Watts, meaning the power supply is slightly less efficient at lower output currents (as is usually the case).

  • Overdriving the 12V rated LEDs to 14.63V improves plug efficiency by 20%.

At the low end, the SS-330W’s minimum output is 4.88V, which yields 12 lux at the counter or a 14x dimming ratio to 7% of maximum illumination, a far better range than is reported for standard dimmer/transformer combinations.

Parts

Raw Data:

LED_power_graph_data

(MS Excel file, you will need the xongrid plugin to update the data as rendered in the graphs)

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Posted at 02:45:36 GMT-0700

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