A lumen print is a solar photogram, similar to the photogenic drawings made by Talbot. The term was popularised by photographic artist Jerry Burchfield, who has worked extensively with the technique. One of the remarkable aspects of this process is that black & white photographic materials produce a range of colours when exposed to the ultraviolet rays of the sun. The range and tonality of these colours depend on the type of material used. Also, expired photographic paper or film can be used successfully. Using these older materials can even result in extraordinary colours that differ from the results obtained with fresh materials. Besides the unexpected appearance of colour, lumen prints are also exceptional because of the simplicity of this process. To make a lumen print no darkroom or specialised equipment is needed. By simply placing a plant or object on photographic paper and exposing this for a sufficient amount of time to the sunlight, an image will appear. The areas of the paper that are shielded from light will remain white. The surrounding areas will darken, the tonality will depend on the duration of the exposure. Many artist and photographers who use this technique work outside with organic materials, especially plants. But artefacts can be used as well.
The phytogram is a variation on the lumen print, using a (phyto)chemical component in conjunction with the effects caused by sunlight. In other words, a phytogram combines the concept of the photogram and the chemigram. The vitamin C and soda solution that is used in phytography creates marks and colourations that differ from lumen prints.