| 摘要 |
PURPOSE:To improve correction accuracy of driving current by providing a current generating unit for generating at least two levels of current and a light quantity measuring unit, and measuring each quantity of light emission by driving a plurality of LEDs alternately with at least two levels of current. CONSTITUTION:Quantity P0, P1 of light produced from an LED for driving current I0, I1 are measured and the characteristic in a section, where the driving current takes a value between 0 and I0, is approximated by a dot line 2 while the characteristic in a section, where the driving current takes a value between I0 and I1, is approximated by a dot line 3. Quantity of light to be produced from the LED is then calculated according to the approximate characteristic of a line graph comprising the dot lines 2, 3. When the driving current is in a section between 0 and I0, required quantity of light P is set according to a formula (P0/I0)/I, whereas when the driving current is in a section higher than I1, driving current I for the required quantity of light P is set according to a formula P0+{(P1-P0)-(I1-I0)}(I-I0). By such method, accuracy of approximation can be further improved by increasing the number of measuring point of the quantity of light. |
