SBRGB
•
8
Another interesting point to note is that for this LED to have enough green
content to match up with the blue and the red components, two elements were
needed! To achieve a good quality white color, we have to provide the proper
current from the driver for each color element. Here is the key to the values
chosen for resistors R1, R2, and R3. We want 20 mA, 40 mA, and 20 mA in
each of the Red, Green, and Blue elements respectively to get a good white
when fully on. After experimenting a bit, we decided to change the scaling to
5 mA, 60 mA, and 10 mA to obtain a nice vivid green and a brighter white
without changing the overall brightness. The low duty cycle (‘on’ time) still
yields a low average current so the slightly higher drive will not harm the green
elements.
LED
COLOR
Lens
Type /
Color
Electrical-Optical Characteristics
(Ta=25C)
Full Viewing Angle
If =
mA typ
Iv =
mcd typ
Vf = V
typ
Ip nm
UL RED
DIF-
FUSED
20
20
1.7
660
HE
GREEN
40
30
2.0
565
UL
BLUE
20
6
4.0
430
60
40
20
0
20
40
60