Garage ceiling lighting

I have just built an 8.5×5.3 m garage/workshop with 2.6 m ceiling height in Sweden (northern Europe). Current status is that it's completed on the outside but the inside is not even insulated. Before completing the interior I want to decide what the ceiling light should look like. The simplest way would have been to just mount a bunch of cheap raised fixtures with T8 fluorescent tubes but my curious personality made me dig into the subject a bit.
When thinking about lighting solutions and looking around how people in general solve this I came up with some insights I thought it could be nice to share.

I'm an engineer but without any expertise in lighting nor electrical installation. So have this in mind when reading this page (which you of course always should when reading stuff on the Internet). Please also note that the facts on non-LED light sources are quite uncertain, I got most of the information from manufacturers datasheets but I did it quickly.

I have deliberately left out most source references and detailed arguments for 2 reasons; 1) It would take me more time to write this page, 2) This page would take people much longer to read.

By light distribution I mean how the light is spread across the room. Having a single spotlight in the middle of a garage will quite obvious be a bad solution. But how many spotlights would be needed to get an even light across the room? I will explain this below. But first I also want to mention that having too few light fixtures will cause uneven light and annoying shadows.

Different light sources/fixtures spread their light in different ways. The datasheets for light sources/fixtures often have a "beam angle" defined. A spotlight can typically have a beam angle of 40° while a tube light fixture typically have 120°. Within the beam angle, the illuminance is at least 50% of the illuminance directly underneath the light source/fixture.
To understand how the light from a light source/fixture is distributed it's much better to take a look at the luminous intensity distribution polar graph. This graph shows the illuminance at all angles from the light source/fixture. It can look a bit complex at first but it's actually very easy to understand. Some of the graphs have 2 curves, typically graphs for tube lights. One curve (C0-180) is the curve across the light source and the other curve (C90-270) is the curve along the light source. The curves simply plot the luminous intensity at each angle from the light source/fixture.

Illuminance calculations

The illuminance at a point directly underneath the light source/fixture depends on 2 things; the luminous intensity from the light source/fixture (which is given by the value at angle 0° in the luminous intensity distribution polar graph) and the height from the light source/fixture to the point of interest.
The calculation is;
E=I/h², where I is the light source/fixture luminous intensity at 0° (in candela) and h is the height (in meters) between the light source/fixture and the point of interest.
An example: We have a light fixture with 600 candela at 0° angle that is mounted 1.7 m above a table. The illuminance on the table directly underneath the light fixture is then 208 lux (208=600/1.7²).

The illuminance at a point away from the light source/fixture is most often defined as the "horizontal illumination". The horizontal illumination is the illumination you get on objects that are placed horizontally, like the floor or a table for example. The wall and a front windshield of a car for example, are not horizontal. The horizontal illuminance at a point away from the light source/fixture depends on 3 things; the luminous intensity from the light source/fixture (which is given by the value at angle 0° in the luminous intensity distribution polar graph), the height between the light source/fixture to the point of interest and the angle between the light source/fixture and the point of interest.
The calculation is;
E=I×cos³(α)/h², where I is the light source/fixture luminous intensity at α° (in candela), α is the angle between the light source/fixture and the point of interest and h is the vertical height (in meters) between the light source/fixture and the point of interest.
An example: We have a light fixture that is mounted 1.7 m above a table and that outputs 550 candela at 30°. The illuminance on the table at a 30° angle from the light fixture is then 124 lux (124=550×cos³(30)/1.7²).

There are free software tools that can help you to simulate the illumination. I have tried 2 of them briefly (DIALux and Relux) and my conclusion is that they work but it takes some time to learn how to use them. And the light source/fixture data must be available from the manufacturer in a correct format.

Guiding rules for placement of light fixtures

To simplify the illuminance calculations above we can state a few guiding rules. h in the formulas below is the height between the light fixture and the lit area of interest (in our case, typically the vertical distance between the inner roof and the table/car hood).

• If the beam angle is 30° the light fixtures should be placed 0.5×h apart.
• If the beam angle is 45° the light fixtures should be placed 0.8×h apart.
• If the beam angle is 60° the light fixtures should be placed 1.0×h apart.
• If the beam angle is 90° or more the light fixtures should be placed 1.8×h apart.
  Explanation to why it doesn't matter if the beam angle is 90° or more: If the light fixtures gives the same amount of light at any angle it will still only give you 35% of the light on a horizontal surface at a 45° angle. The total contribution beyond 45° will be much less since almost all light fixtures (the exception would be the cheapest fluorescent tube fixtures that lacks reflectors) will have a significant decline in their illuminance beyond a 45° angle.
• If the light fixture produce a round spot (for example NOT a tube light) they should be placed in a zig zag pattern.

The above list is only valid for light sources/fixtures that emit light evenly in all directions onto a surface. This covers most light sources/fixtures but not tube lights and LED strips. Tube lights and LED strips can be considered as an array of small light sources. Each of the light sources in the array will behave as an ordinary light source. So tube lights and LED strips can be placed according to the list above in one direction but in the other direction (end-to-end) it gets a bit more complicated.
To understand this I made some simulations and came up with an equation for spacing tube lights and LED strips in the end-to-end direction:
spacing = h - source_length/2, where spacing is the distance from the end of one tube/strip to the start of the next tube/strip, h is the height between the light fixture and the lit area of interest (in our case, typically the vertical distance between the inner roof and the table/car hood) and source_length is the length of each tube/strip. Use same unit for all three dimensions. The equation assumes that the C90-270 intensity parameter is according to most current LED light sources. I have looked at the polar graphs in the datasheets from the LED tubes heading further below in this page. The equation should result in an illumination that varies with no more than 20%. And yes, the longer the tubes/strips, the shorter the distance between them.

Examples of different light sources/fixtures

In the graphs to the right you can see real world examples of the light distribution from 3 different light sources/fixtures. It can be seen that the example fluorescent tube fixture provides a very even light within 90°. The LED spot shows the characteristic beam. The example LED tube shows that about 15% of the light is emitted outside of 120°. The reason for this "waste of light" is most likely the diffuse plastic cover around the tube. A fixture with a good reflector is needed to direct this light more downwards.

By "MR16/GU10 type" light fixtures I mean small recessed housings with a directional light source. The most common form factor is the MR16 and it's GU10 derivative. The light source can be halogen, LED or fluorescent.

The GU10 is run from mains voltage (120/230 VAC) while the MR16 also can be specified to be powered from a lower voltage (12 VDC).

It seems as MR16/GU10 halogen light sources rated at 50 W produces somewhere between 300 and 800 lumens. Halogen light sources has the disadvantage that their lifetime is quite poor, at least when running at full power and from a mains voltage.

MR16/GU10 with LED as light source consumes much less power and has a longer lifetime. However, to get a luminous equivalent for the 50 W halogen we must look at for example OSRAM's MR16 rated at 620 lumen. It consumes 12 W (which seems like a bit much, I'm sure there are better alternatives out there).

A rough cost estimation for using halogen GU10 with fixtures in my garage is 39×($4+$6)=$390.

A rough cost estimation for using LED MR16 with fixtures and AC/DC converter in my garage is 39×($30+$6)+$75=$1480.

Large downlight light fixtures have 2 main advantages over MR16/GU10 lamps; they have a larger light emitting area which gives them a better light distribution and they can deliver more light. The light source can be of several types but CFL and LED seems to be the most common.

As an example of a Large downlight LED light source/fixture one can mention OSRAM's 180 mm LEDVANCE XL WT which gives 2000 lumens while consuming 19 W.

A rough cost estimation for using large downlight LED light sources/fixtures in my garage is 15×$160=$2400. Another alternative is to buy used large downlight CFL sources/fixtures for around $20 each.

The LED panel is more or less the same as the Large downlight LED light fixture. The main difference is that they are larger, normally 60×60 cm or 120×30 cm.

The fluorescent tube (T5 or T8) is quite cheap, cost is about $5 for a high quality tube. The price for the fixture is more difficult to say. There are very cheap fixtures. For T8 tubes, the cheapest fixtures has a magnetic ballast and a starter that causes flickering light and consumes about 20% additional energy. The electrical ballast, which is required for T5 tubes, is much better since it consumes less energy, turns on the light faster and in some cases allows dimming. The downside is that it adds cost to the fixture. After doing a quick web search it seems as you can get the cheapest 1.2 meter fixtures for about $30 while the ones with better quality/efficiency costs at least twice as much. Another option is of course to buy used fixtures.
One very important thing to consider with fluorescent tubes is the fixture luminous performance. Note that my definition here of luminous performance is how much of the light from the light fixture that is used on the surface below (a table for example). Since the tube is omnidirectional the light must be directed downwards. The simplest fixtures lack reflectors and my guess is that the luminous performance will be in the range 40%. The better performing fixtures can reach about 70% luminous performance.

The luminous output from a tube varies with make and model but a quick look at OSRAM indicates that a standard 1.2 meter T8 tube delivers 3,300 lumens and that a High Output T5 tube delivers 4,300 lumens. The lumen output figures from the fluorescent tube manufacturers is only valid when using a "ballast factor" of 1. The "ballast factor" defines how much power the ballast will supply to the fluorescent tube. The luminous output from the fluorescent tube will be the fluorescent tubes specified luminous output × the ballast factor. The ballast factor is normally around 0.9 but can be in the range 0.7-1.2.
If I would use standard T8 tubes in my garage I would need about 8 of them if I use a very good fixture to get my desired 500 lux, in case I use very poor (cheap) fixtures I will almost need to double this. 8 light fixtures would give me an even light distribution if I spread them out across the ceiling. The cheapest light fixtures tends to always use 2 tubes (at least in Sweden) and this will compensate for their lack in luminous performance. The total efficiency will however be quite poor.

One must not forget that the luminous output of fluorescent tubes are sensitive to temperature. If they are to be used in a garage with none, or very little heating, the fixture should be of a sealed type. Perhaps one should also use "High Output" tubes.

I want recessed fixtures since I think it's stupid and ugly to have the fixtures hanging down in the room. But this showed to be a bit problematic since I wanted to mount them in a certain direction.
My roof trusses are placed 1200 mm apart an I want to mount drywall panels on them using 28x70 mm ceiling joists. This means that if the lighting fixtures are wider than 1150 mm they can't be thicker than 41 mm (13+28 mm).
I had problems finding a fixture that was thin enough (<41 mm). After searching the web I found the "Zero Plenum© Troffer" from Columbia LIGHTING. This would do the job but they seem to cost more than $200 each and this is way above my budget. Perhaps there are cheaper alternatives out there.

A rough cost estimation for using fluorescent tubes with the cheapest fixtures in my garage is 8×($5+$5+$30)=$320.

A rough cost estimation for using fluorescent tubes with simple but high performance fixtures in my garage is 8×($5+$60)=$520.

A LED tube is meant to be a direct replacement of a fluorescent tubes. There is however one major difference; the fluorescent tube is omnidirectional in its light distribution. All LED tubes I have seen have a beam angle at around 120-160°. So in most cases, there is little need for a light fixture that directs the light downwards.
Replacing a fluorescent tube for a LED tube is however not as simple as one might think. The fluorescent tube is powered by a ballast and the output from the ballast is, depending on type of fluorescent tube, a voltage and current. The magnitude of the voltage and the current depends on the type of ballast. To cope with this, the LED tube manufacturers have come up with different type of solutions.
A few years ago most LED tubes were powered from only one side of the tube, some of them left the unpowered end unconnected while others shorted the 2 pins on the other end. These LED tubes requires the fixture to be rewired.
Nowadays it seems as most LED tubes are powered from both sides, just like a fluorescent tube. The advantage with having the tube powered from both sides is that you can use the LED tube as a direct replacement for a fluorescent tube, without having to rewire anything. To handle different ballasts, the LED tube manufacturers specify which ballasts they are compatible with. Some of them allows the fixture to be rewired so that the ballast can be removed but some requires a correct ballast to be present. So always consult the LED tube documentation before replacing a fluorescent tube with a LED tube.

Most LED tubes comes in T8 form factor. The reason is probably because most installed fluorescent tubes are of T8 type and because the T5 tubes are good enough to keep.

As of now (Q1, 2015) most high performance T8 120 cm (4') LED tubes have a lumen output of 2000-2500 lumen. This can be compared with a standard T8 fluorescent tube which has a lumen output of 3000-3500 lumen. The LED tube will in most cases loose less of it's output in the fixture so the real difference is not so big.
The high performance T8 150 cm (5') LED tubes have a lumen output of 3000-3500 lumen.

To get the highest efficiency, one should remove all electronics and everything in the fixture that is in the way of the light (lens and louvers).

Important note regarding LEDs; the cheaper ones are cheap for a reason. I strongly recommend that you use the ones that are made by serious companies.

In theory the LED strip is easy to install (just use the self adhesive tape to attach them to the ceiling) and very cheap (from a few dollar per meter). First we need to figure out how powerful the LED strip must be. In my garage I would want them to run along the long section of the ceiling, hence be about 7.5-8 meters long. I think that 2, 3 or 4 of them would be good for the light distribution. Currently, LED strips produce about 80-100 lumens/watt.

• Using 2×7.5=15 meter they would need to produce 1600 lumen/meter. This translates to about 18 W/m.
• Using 3×7.5 meter they would need to produce 1070 lumens/meter, This translates to about 12 W/m.
• Using 4×7.5 meter they would need to produce 800 lumen/meter. This translates to about 9 W/m.

Using LED strips that are rated above 10-15 W/m will in most cases require them to have extra cooling. At least cheap LED strips don't have enough heat spreading material so they will deteriorate (burn up) very quickly. A way to solve this is to mount them on an aluminium profile but these are quite expensive and they require that the adhesive on the back of the LED strip is of very good quality (very cheap LED strips most certainly do not use 3M adhesive, even if it says so).

Most of the LED strips use series resistors to regulate the current. This is very simple and cheap but means that it's impossible to achieve high efficiency while keeping the luminous output constant over source voltage variations, LED tolerances and temperature variations. LEDs with no active regulation also suffer from "thermal run-away" (they get hotter and therefore consume more current and therefore get even hotter...). Active current regulation is much better since it can provide a more even luminosity at a high efficiency. The active current regulation can also protect the LEDs from overheating since it can be designed to reduce the current if the temperature rises. The power conversion efficiency for most LED strips, with series resistor or active current regulation, will be about 75%. 15% is lost in the LED strip current regulation and 10% is lost in the AC/DC voltage converter.

One more thing to consider is the surface protection. I want some sort of mechnical protection for the LED strip and this can be achieved in 2 ways; using an aluminium profile that also contains a plastic cover or use a LED strip with some sort of transparent coating. Both of these solutions costs money. The transparent coating also has a potential problem, if the coating is made of an inappropriate material, it can become less transparent when aging. The coating will also have a negative impact on the cooling and luminous efficiency (at least 5-10% loss of luminosity).

An important note when using the LED strip in a non-heated garage is that the temperature variations will stress the self adhesive tape on the back. This will cause the strip to eventually fall of the ceiling. OSRAM recommends that their LED strip is cut every meter to reduce the stress in installations with varying temperature.

LED strips generally have the same light distribution as LED tubes so look there for a more detailed description on how to space them to get an even light.

The only LED strips that I found usable (OSRAM, Barthelme, Solarox, Flexfire LEDs, Solid Apollo LED, Diode LED and LED World for example) were quite expensive.

A very rough cost estimation for using LED strips in my garage is $1000.