Photo Cornucopia   Home    

Battery powered 18 Watt fluorescent light for light painting cars


John Jovic

This article describes the construction of a compact and portable 12 volt powered 18 Watt fluorescent light (not LED) which is suitable for light painting cars at night or it could be used for other painting with light applications.
The light is a standard 18W household fluorescent tube in a sturdy housing.  

Battery powered, in this case with 1 hours worth of AA NiMH goodness!

The light is built into an aluminium housing which is compact and light enough to use comfortably. This housing contains the 18 Watt fluorescent tube which is 590mm in length, the electronics (the inverter) which converts the 12 volt from an external battery or power source into the high voltage needed to operate the fluorescent tube, a power socket and a power switch.

Nuts and bolts

WARNING: Fluorescent lights and inverters are high voltage devices so are potentially dangerous. If you don't know how to safely wire, or operate these kinds of devices then do not attempt to do so, and if you do, then do so at your own risk.

The principals described below can be modified to suit your own application so you could build a light which uses multiple tubes or possibly tubes of greater length and power. Ultimately everything will need to fit around the inverter that you use so a stronger inverter for a larger tube (eg 36W) may require a larger case to fit it.

A brief parts list, listing only the major components, is as follows. The cost will depend on the components used and the most expensive will probably be the inverter.
Item Approximate Cost
12 volt to 18W Fluorescent Inverter (to suit 15W-20W tube) $50
T8 18W fluorescent tube to suit $4-20
T8 fluorescent lamp holders (or tombstones) $2 each
on/off switch $3
input socket $3
fuse holder/fuse $5
aluminium case, fasteners, wire, Velcro, tape, heat shrink etc. $10-30
suitable battery ?

18 (left) and 36 Watt (right) lamps are show here for comparison. The 36W fluorescent lamp is described in the article Battery powered 36 Watt fluorescent light for light painting cars

The Fluorescent Inverter is a form of Electronic Ballast and is the heart of the light as it converts a low voltage direct current (DC) into a high frequency high voltage alternating current (AC) which is applied to each of the 2 filaments at the ends of the fluorescent tube. Note that Fluorescent Inverters are not normal DC to AC Inverters which are designed to convert DC to household voltages at 50/60Hz. Also note that normal Electronic Ballasts typically work at mains voltages and not from low voltage DC sources such as a 12 volt battery. Fluorescent inverters are available in many configurations of input voltage and output load (type of fluorescent light) so choose one which suits the fluorescent tube that you want to use. They can be sourced from specialist solar, camping, off-road or similar suppliers dedicated to low voltage equipment. The inverter used here is designed to operate 15W-20W tubes.

Inverters must be wired strictly as per the manufacturers instructions.

The Inverter is connected to the battery via a socket and a power switch which is suitable for the current load. It's also a good idea to install a fuse to protect against electronic faults or short circuits (refer to the Inverter manufacturers recommendations). The wiring used must be suitable for the high voltages supplied by the inverter, again refer to the inverter manufacturers recommendations.
The 12 volt inverter fits neatly into the housing. The inverter produces high voltages to drive the fluorescent tube so safety precautions must be taken to ensure that these high voltages can never be contacted accidentally.  

The fluorescent lamp holders are often called tombstones and are available in many shapes and sizes depending on their intended application and how they will be attached. These are for T8 tubes.

The housing is made from a 40mm aluminium extrusion because that particular extrusion allowed the inverter and other components to fit neatly inside. You might have to use a larger extrusion depending on the inverter used. Aluminium extrusions are available in a bazillion sizes and you can even have them moulded to your own dimensions if you really want to, but you'll probably have to make a 250Kg batch of them! It's easier to just see what you can get from importers or suppliers in your area and just make it work for you.

The tombstone lamp holders are fitted on a simple angle bracket and wired from below.  

Identical tombstones are used at both ends of the housing.

Black non reflective tape was used on the external surfaces of the housing so that it didn't reflect any ambient lights and therefore appear in images.

The aluminium housing has a socket for power. Any kind of 12 volt battery could be used.  

The battery holder is attached to the housing using Velcro hook and loop strips and can be positioned so that it doesn't interfere with holding the light.

The 12 volt power source is a group of 10 AA NiMH 2000mHh batteries which are wired in series. I used NiMH batteries because I have lots of them, as do most working photographers. This battery pack is capable of powering an 18W tube for approx 1 hour but you could use higher capacity NiMH batteries, or just bring a spare set. Any 12 volt battery could be used as long as it is capable of supplying the moderately high continuous current of 1.2 Amps. NiMH batteries are quite good at supplying that kind of current for extended periods and I found that the batteries where cooler after 1 hour of continuous operation than they are after heavy use in a Canon 580EXII flash!

Does it work?

Yes, and quite well too. It's not too heavy, cumbersome, dim or anything else. It provides an evenly distributed light at about the the right intensity however this will always depend on which aperture and ISO you want to use.

For those unfamiliar with automotive light painting a full description of the technique can be found in the article Automotive Lighting 8:
Painting with Light.

This is one of the first test images shot with this light and is a composite of the two images to the right.  

Shot at F8 at ISO200 for approx 35sec. In this example a 4000K tube was used and it seemed to balance quite well with the Sodium (yellow/amber) street lights.


Shot at F8 at ISO200 for approx 35sec. The background image was processed at the same colour temperature as the light painted image.

The test images above where shot with a 4000K light source, which allowed the background colour to blend fairly well with the light painted image however a different colour could have been used for effect. If a 6500K tube had been used, which is quite blue, then the background would be a far deeper amber colour. 5000K tubes are also quite common and balance fairly well with flash and Metal Halide street lights (the white ones).

Fluorescent tubes are normally available in a choice of colour temperatures typically from 3000K-6500K. Choosing the right colour temperature tube for the ambient light will have a significant effect on the colour balance.  

The reflection of the light in this cars panels is quite effective. It can of course be made much smaller by simply shading or covering part of the light source, or you could just use a more appropriate light if you want a smaller highlight.

Fluorescent tubes have a minor inherent disadvantage in that they take a little while to warm up before they reach maximum light output. When the tube is first switched on it is cold and may produce a full stop less light then when it is warm. Once warm it will produce a relatively consistent light even if switched off for short periods so in practice the difference in light output is generally insignificant.


Why didn't I just use an LED strip? The LED's in LED strips are usually spaced apart so their reflection in a car panel can potentially appear as multiple lines instead of a continuous strip. Although steps can be taken to diffuse these spots of light into a long continuous strip, such as simply placing a diffusing material in front of them, a fluorescent tube is inherently a much more evenly illuminated source so is a better choice in this respect.

If you are looking for the cheapest option then just wander off to your nearest hardware or aftermarket auto store where you can buy a very similar fluorescent or LED 'work light' for relatively little cost. Such a light would need a few minor modifications, maybe just a carefully placed reflector or cutter (shield). However I wanted something that was potentially more sturdy, effective and possibly one I could expand with additional tubes if needed, so I decided to make my own. But I'm an electronics geek and I like doing that kind of thing anyway.

  Copyright 2015 Photo Cornucopia

Contact Terms