Light is part and parcel of solar radiation, the requirement of which varies with species. Various species show varying tolerance to light intensities. But they depend on stages of development, eg. Sal is light demander, but requires partial shade in the beginning or earliest stage. So, to classify the species, detail information on conditions of species are required. On this basis, they are classified as follows:

1. Light demander: A species that requires abundant light for its best development, eg. Sal, Teak, Banjh, Khote salla, Gogre salla, Sissoo, Simal, etc.
2. Shade bearer: A species capable of persisting and developing under shade, eg. Deodar, Bijay Sal, Khashru, Cuppressus torulosa, Picea smithiana, etc.
3. Shade demander: A species requiring some degree of shade at least in its early stages, for its normal development, eg. Sindure, Jamun, Loth salla, Abies pindrow, etc.

Importance

1. Chlorophyll Formation: Light of any wavelength or low intensity is sufficient to form chlorophyll. Without light, plants become pale yellow and have thin internodes, a condition known as etiolation. Chlorophyll decomposes in bright sun light; thus formation and decomposition both go on simultaneously when the plant is exposed to light.
2. Functioning of stomata: Light influences daily opening and closing of stomata, which affects respiration and photosynthesis.
3. Photosynthesis: The light used in photosynthesis is a small amount of the total light that falls on a leaf. It has been estimated that light used in it is less than 2% of the light energy incident on well-illuminated leaves. There is usually sufficient light even in dense forest for this important physiological activity.
4. Growth: Forest trees generally require about 1 to 1.5% of the full sun light in moderate intensity of light. The best growth takes place in moderate light if food is available. Quality of light refers to the wavelength of the light spectrum or colors. Violet and ultra-violet light bring about dwarfing effect. Photoperiod varies with altitude and latitude (photoperiod is the relative length of day and night to which the plant is exposed). Light affects breaking of dormacy, germination, leaf fall and flowering. Extremely high intensity of light increase transpiration excessively, stem remain short and develop smaller leaves.
5. Form and quality of trees: Height growth is retarded in intense light conditions. Trees growing is shade are usually taller than those growing in open. Light causes formation of relatively large crown and so rapid growth.
6. Species stratification, size and structure of leaves: Full light reaches the top canopy and lower canopies receive only escaped light results in the stratification. Light also affects the size, colour and structure of leaves. The leaves exposed to full light are smaller than those in partial light. Many forest trees develop different anatomical structure in their leaves in shade as compared to those grown in sun. Light also affects the arrangement of leaves.