Light Bleaching on Holy Grail kush

First time ive had this happen but my 400w is bleaching the leaves of my Holy Grail Kush. I put a thermometer probe right above where the bleaching is happening and temp never exceeds 80f, but it is clearly bleaching the leaves and turning them yellow on the tops closest to the light. How damaging is this to the plant? i moved the light away i figure that will solve the problem is this a strain specific thing or am i just giving the plant too much light? I have a 400w HPS in a glass enclosure with air cooling and have had it about 6-8 inches from the plants in a 2.5x2.5x5ft tent.

Picture is worth 1000 words

If you know it's light-bleaching and you can move the light up, do so. 6-8 inches sounds too close to me, but I don't know your light.

ya i have never experienced this tho, i always thought the light distance was only an issue with heat but i guess this strain just cant take the intensity of my HPS that close. Live and learn.