Light from fluorescent lamps can induce formaldehyde production and iron deficiency in plant nutrient culture medium. Formaldehyde is produced from EDTA when it is oxidized by the photochemical reduction of ferric iron and it can accumulate to inhibitory levels. The medium becomes iron deficient because iron becomes unchelated and forms an unavailable precipitate as EDTA is oxidized. The combination of light-induced formaldehyde production and loss of available iron reduces the ability of the culture media to support growth of Arabidopsis thaliana roots. Removing ultraviolet and blue wavelengths with a yellow acrylic filter is a simple and effective means of preventing Fecatalyzed photooxidation of EDTA in plant culture media.