The sin bt can only take values between one and zero (definition of sin)The maximum of sin bt must be on at 1, when the maximum value of I occurs. Divide l = 610 by 1 to get a = 610.
If sin bt is equal to 1, the inverse sin will give us a value of bt = 90 degrees ( the value will be different from radians, bt = 1.57). assume the midday is the halfway point of the 12 hours of daylight, t = 90/6 = 15.
Therefore l = 610 sin 15 t where t is hours after sunrise.
If I understand your problem correctly.
