Abstract
Light is a very important factor affecting plant growth, development and production. Glasshouse is a good environment for altering lighting. Therefore, we can change light properties affecting plant growth. In a glasshouse and field study we have investigated how light intensity, influence onion plant morphology and bulbing. Light levels to individual plants were reduced either by using artificial materials for shading or altering leaf density. The effect of reduction of incoming solar radiation was similar in both two methods. Individual plants were generally larger under higher light levels. Total leaf area, leaf dry weight, bulb size and bulb dry weight increased as light intensity increased. Plant efficiency was changed by altering plant density and shading levels. Efficiency was increased by either increasing plant density or reducing light intensity.