The time structure and spectra of X ray and extreme ultraviolet (EUV) bursts during solar flares are described from the viewpoint of evaluating their ionospheric effects. The impulsive flare component is strong in emission from solar source regions with temperatures in the range 104¿K--106¿K, which are strong in the 90- to 1027-¿ range. The strenght of the impulsive EUV emissions incident on the ionosphere depends on the location of the flare on the sun. The impulsive EUV emission produces short-lived large absolute enhancements of photo-ionization rates above the bottom of the preflare E layer and in the F region. The slow components are very strong in emission from solar sources with temperatures in the range 1--30¿1060K and are particularly strong at soft X ray wavelengths (1--90 ¿). Thw slow 1- to 8-¿ burst causes the large percentage increase in ionization production below the bottom of the preflare E layer and in the D region. The large absolute flare emission in the 8- to 90-¿ emission and the K shell absorption edge of N2 near 31 ¿ causes the large slow enhancement of photo-ionization in the 100- to 130- km altitude range.