Here is how I did a quick light painting photography shoot I did a few nights ago using a string of battery-powered RGBY (red, green, blue, yellow) LEDs.
Lets look at the set-up first. Sometimes in light painting you want to show the subject in a scene and in other cases you want to have the background black so the subject is the only thing in the image. In this case I wanted a dark background as I wanted to focus just on the bottle and the light streaming out of it so I set up a dark backdrop and base. I used black foam core board for the backdrop and a piece of black material for the base.
For this light painting shot I was using my Canon 1D IV with a 24-70 f2.8 lens which was set towards the top end of the focal length as I wanted a reasonably narrow field of view. In this case the focal length was 62mm. As a starting point for the exposure I used f13 for the aperture and ISO100 for the sensitivity. Because I have a remote shutter release cable the camera was set to ‘Bulb’ mode. About half of the LED string was loaded into the bottle and set into place on the base for each of the exposures.
For each of my attempts at this light painting image I started pulling the LED string up before I started the exposure. This meant that I avoided have any bright spots in the exposure above the opening of the bottle from the LEDs being static. You will notice that inside the bottle there are some significant bright spots towards the bottom where the LEDs were not moving during the exposure.
I experimented with a few different aperture settings and the speed at with I dragged the LEDs out of the bottle. My favorite exposure ended up being at f20 and went for 8 seconds in Bulb mode. The sensitivity remained at ISO100. I also found that I needed to pull the LEDs quite fast as some of the initial exposures were around 19 seconds and the colors from the LEDs ended up being blown out to white.
Adobe Lightroom was used for a small amount of post processing where I decreased the contrast slightly (-10) and drops the blacks a little lower (-10). This was done to improve the appearance of the light trails against the background.
In the future I would like to try this using an opaque or semi-opaque vessel so you cannot see the static LEDs in the image. I also intend to add some indirect light painting to highlight the bottle. In the end this is a fun and simple light painting project anyone can try. All you need is a camera with a long exposure mode and a cheap string of LEDs.