How close can I get with a 400 W HID to some 3 week seedlings

I have like 50 seedlings in solos with an old Hortilux 400 HID @ around 3 feet atop. I'm just wondering how much closer I can get. Day temps are hot 30c, nites are like 21c. At nite is when I would like to lower them then raise them in the morning. I'm guessing it's a good idea as long as I don't burn them hey? IDK I'm new to HID lighting and indoor growing any advise is appreciated. Thanks.

For mature plants I normally keep my 400-600 watt hid lights no closer than 500 mm (1.5 - 2 feet). Clones and seedlings should be fine at 3 feet (Maybe closer if shaded by larger plants). Although CFLs and/or low wattage fluorescent lighting can be a lot closer with no issues. 50 mm (1 - 2 Inches)

Thanks Mr Jaw. I've been lucky in the flower room, the lights there are 1k at about a foot away. I guess the air cooled hoods help.