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Multi-LED tube lights can cast multiple shadows?

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treez

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Hello

Apparently, “Tube lights” when done with LEDs (instead of fluorescent technology), mean that each LED casts a shadow on the floor below it…and this means that a diffusor must be placed over the LEDs to avoid this multiple shadowing. Is this true?

The diffusor means that light energy is wasted, and therefore, its inefficient to make tube lights with LEDs...instead, LEDs should only be used in "spot" lights.

Here is an example of a LED tube light with multiple leds side by side
http://www.ledison-led-lights.co.uk/p/Ledison+T8+LED+Tube+240cm+35W/58.htm
 

betwixt

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True, but consider there are 564 LEDs in the space of 2.4m and each has a fairly wide emission angle. Any shadows will be very indistinct, even on the clear glass tube. The version with frosted glass (if it is glass!) will 'fuzz' the individual lights but most of the light will still get through. Some will be internally reflected but then given a second chance as it reflects back off the internal surfaces.

More important on that type of light is the lack of light leaving sideways and behind them. In most conventional fittings a lot of the light reflects back from the ceiling but those tubes only radiate downwards.

Brian.
 
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andre_teprom

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If you consider that the light intensity of the LED has a smooth variation according to angle displacement, in theory the light superposition of a LED array nearly clustered should give a smaller variation on radiation shape.

Anyway, once this could strongly depend on geometry of each arrangement, a simulation could provide an accurate extent of such effect. This procedure is usual on designing of light sources for cameras used on specific industrial applications which requires a constant light pattern along the region of interest of a plain surface.
 
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treez

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I agree, i think "shadcows would be indistinct", but we've just had a top lighting designer tell us that we should do a led office light by using a single high power "multi-led" spot, because it will not give the shadows associated with the described multi led tube lights.

I wonder if he means that the light from led tubes is not "even", and he kind of calls that effect, "shadows"?
 

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I would have thought any spotlight will cast more hard shadow than any distributed source. It's nothing to do with LEDs per se, it's just trigonometry.
Perhaps they are thinking of an older tube replacement they have seen. Modern ones, apart from the uplighting, are as good as fluorescent tubes. Most office 'strip' lighting these days is recessed into the ceiling with reflectors behind the tubes so although the aperture in the ceiling (I'm hesitant to call it luminaire) may appear darker, the same amount of light will be radiated downwards.

It's worth considering that a snapshot of a fluorescent tube will show uneven light levels along it's length anyway.

Brian.
 
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betwixt

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That looks more like factory lighting than office lighting. I've seen the pre-LED versions used in huge industrial unit where they hang from the roof, maybe 4m or more above the floor. At that height the beam is diffuse and covers a large area but they do cast harsh shadows. Speaking from experience, they are unpleasant to work under!

Office lighting is generally < 2.5m above floor level and designed so there is a large overlap between light sources so the shadowing is minimized. Most office lighting is recessed in the ceiling with barriers to prevent direct line of sight to the tubes unless you are right underneath them.

Brian.
 
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