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During the electrical lighting system failure at work on a grey rainy day I was stuck with 400W metal-halide reflector lamp as the only source of illumination. Thing radiates about 38.000 lumen, so I pointed it to the ceiling, and kept on working in my office. To my surprise, the effect of the so diffused light was much like sunny summer day, and sometimes on November days (live in the central Europe) I play with the idea of firing it up just to improve my mood, although 400W nowadays is quire a waste of energy :)

On the other hand, my apartment is facing north and it is in at the first floor of the 7 floor building, so November days are dark and gloomy even with moderate cloud cover. I am constantly searching how to improve lighting and feeling in the apartment, and I remembered that metal-halide floodlight which made such a huge difference at my workplace one day.

I am an electrical engineer, btw.

So I got the idea of buying the LED floodlight,daylight color, about 100W, and pointing it to the ceiling in my living room. But here immediately lies the problem: instructions for all floodlights explicitly say that it has to be at least 1 meter away from the surface it illuminates. Why?

I understand that problem when people were using 500W halogen lighbulbs, which generated enormous amount of heat and IR radiation. Couple this with dark wooden surface, and there may be some serious fire risk.

But why shouldn't I mount a 100W (or even 200W) LED floodlight, mount it about 20 centimeters (1 foot) below the ceiling and point it upwards? The material is concrete, painted over with white chalk-based indoor paint (which I am pretty sure is as non-flammable as concrete).

So, the question is:

  • Why all manufacturers specify that distance to the lit material even with LED reflectors? As far as I understand, white LED spectrum is determined by the phosphorous used as the final stage of light generation and looks like this: https://cdn.shopify.com/s/files/1/1041/2564/files/warmNcool_large.jpg?v=1472124974 which should really not be a problem, especially when the ceiling is covered in white paint

  • Any other reasons I should not attempt such installation?

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  • I'd try it, and monitor the temperature of the surface. Get the conditions as extreme as possible and see if it gets dangerous; if not, then back off by a factor of 2 and call it a day.
    – Daniel Griscom
    Nov 20, 2017 at 0:48
  • The problem with the 500W halogens is dust or FOD would accumulate on them (e.g. T-shirts draped over them for drying) and they would set that on fire, chaining to other house dress, or someone would knock a lamp over to the same effect. I am expecting torchieres to make a comeback now that they can run cool as LEDs.
    – Harper - Reinstate Monica
    Nov 20, 2017 at 1:45
  • aside: a lot of LED floodlights flicker (driver-less ones); not good for indoor primary lighting. 1' is fine.
    – dandavis
    Nov 20, 2017 at 2:15
  • @dandavis You casually mentioned flicker - thank you for this, actually this is the single best reason to not rush into such installation. I did not yet buy LED floodlights, but tried to with metal halide floodlight, and it really bothers me if I use it for too long. So the first thing I need to check is the flicker. I found this: electronics.stackexchange.com/questions/19256/… and I expect floodlights are much worse flicker-wise as ordinary lights.
    – xmp125a
    Dec 21, 2017 at 17:14
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    it totally depends on the floodlight. there are cheap ones based on cheal LED modules that accept raw AC. those flicker. Others have an AC-DC converter, like a meanwell constant current driver. look for language mentioning "DC", "SMPS", "Constant Current", "PSU", etc. good ones don't flicker a bit.
    – dandavis
    Dec 22, 2017 at 5:45

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I think it is a CYA situation. What would we do without lawyers? I would point the beam somewhat at an angle so you won't get radiation bouncing directly back at the light source. Otherwise, I see no problem. Shine-On!

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