Not sure but this may help someone. We received our chicks last Friday( Californian whites) we only had a 250w white buld on hand so thats what we used. Tuesday we got a 250w red buld. From what we have observed going from white to red is the chicks seem more calm. With the white they were restless and very noisy. Now with the red they make almost no noise(just peeps) and we see them resting more also.