You had the correct insight. The afternoon slump can occur with or without depression. If you measure the interval between the slump and the midpoint of nighttime sleep, they’re about 12 hours apart. (This is separate from the “post-prandial” slump some people experience after a heavy midday meal.) You don’t need to spend all day in “blinding bright light” to counteract the slump. The principle is to get to the light box as soon as you sense the onset of the slump, and not wait until it gets severe. This can nip the slump in the bud, even with 10,000 lux light exposure as short as 10 minutes. Some people will need longer, so you’ll need to experiment. There are days when the slump comes a bit earlier or later, so don’t set the light session by the clock. Rather, be attentive to the onset of the slump. This technique works for many people, but not for everyone. If it fails, and you have control of your work space, raising ambient light level in the afternoon to about 2000 lux – from ceiling or desk fixtures – including the light box – is another approach. Don’t overdo it, however, or you may experience jitteriness, headache, eyestrain, or sudden mood shifts that interfere with work.