OT: How to compare LED lamp and discharge lamp video project

[N_Cook]

The Lumens rating is irrelevant as its comparing chalk and cheese.
All the LEDs can have their axial (principal) light outputs aligned to the
light tunnel but only the smallish fraction (anyone know what this fraction
is ?) of a discharge lamp output can be so directed, as not a point source .
It can only have some proportion of the say 50 mm diameter of parabolic
reflector opening aperature, directed to say the active 10mm diameter or so
of the colour wheel.
What is needed is the W/ sq cm of a 100 percent bright white video image as
received at the screen for a set diagonal at the screen. Anyone know of a
chalk versus cheese factor for converting the lumens ratings of both types ,
for comparison purposes?

 

[josephkk]

On Wed, 8 Aug 2012 14:09:39 +0100, "N_Cook" <diverse@tcp.co.uk> wrote:

The Lumens rating is irrelevant as its comparing chalk and cheese.
All the LEDs can have their axial (principal) light outputs aligned to the
light tunnel but only the smallish fraction (anyone know what this fraction
is ?) of a discharge lamp output can be so directed, as not a point source .
It can only have some proportion of the say 50 mm diameter of parabolic
reflector opening aperature, directed to say the active 10mm diameter or so
of the colour wheel.
What is needed is the W/ sq cm of a 100 percent bright white video image as
received at the screen for a set diagonal at the screen. Anyone know of a
chalk versus cheese factor for converting the lumens ratings of both types ,
for comparison purposes?

There isn't one nor can there really be one. The biggest part of the
issue is that the spectrum of each lamp type is different. The Lux to
Lumens conversion requires specific assumptions about the spectral
intensity curves. No real lamps meet these requirements. See Color
Rendereing Index (CRI) as well.

That said, lumens rating gives a reasonable approximation of how much
humanly perceived illumination can be expected for any lamp.

BTW decent arc lamps can be focused pretty well, it is not all that
extended of a light source. For ugly try line filament incandescent
lamps; of course when you want a line of illumination (photocopiers) they
may be nearly indispensable.

YMMV

?-)

 

[N_Cook]

josephkk <joseph_barrett@sbcglobal.net> wrote in message
news:kvno289blqc3blpsvve8jn1mgsebf90atr@4ax.com...
On Wed, 8 Aug 2012 14:09:39 +0100, "N_Cook" <diverse@tcp.co.uk> wrote:

The Lumens rating is irrelevant as its comparing chalk and cheese.
All the LEDs can have their axial (principal) light outputs aligned to the
light tunnel but only the smallish fraction (anyone know what this fraction
is ?) of a discharge lamp output can be so directed, as not a point source
..
It can only have some proportion of the say 50 mm diameter of parabolic
reflector opening aperature, directed to say the active 10mm diameter or so
of the colour wheel.
What is needed is the W/ sq cm of a 100 percent bright white video image as
received at the screen for a set diagonal at the screen. Anyone know of a
chalk versus cheese factor for converting the lumens ratings of both types
,
for comparison purposes?

There isn't one nor can there really be one. The biggest part of the
issue is that the spectrum of each lamp type is different. The Lux to
Lumens conversion requires specific assumptions about the spectral
intensity curves. No real lamps meet these requirements. See Color
Rendereing Index (CRI) as well.

That said, lumens rating gives a reasonable approximation of how much
humanly perceived illumination can be expected for any lamp.

BTW decent arc lamps can be focused pretty well, it is not all that
extended of a light source. For ugly try line filament incandescent
lamps; of course when you want a line of illumination (photocopiers) they
may be nearly indispensable.

YMMV

?-)

+++++++


Someone demonstrated to me a Philips PPX2480 in an industrial discharge-lamp
floodlit sales barn . On battery so 55W , not the mains 80 W lumens, but at
about 7 foot diagonal so probably about the same as 80W on 10 foot diagonal
, stated max in the specs. But would be totally inadequate. In a darkened
room it would be fine but the operational requirement here is for use in a
daylit, but indirect sun, room with some , non-blackout, curtains drawn if
necessary or room lighting sufficient to read printed paper.
So looks like 300W (LED lumens rating) at least for my purposes for 10 foot
diagonal.
Still don't know what that equates to in discharge-lamp projector Lumens

 

[N_Cook]

The current projector was rated 1700 lumens, 200W, but is probably reduced
output these days , but still useable in those room lighting conditions at 8
to 10 foot diagonal

 

[N_Cook]

I see Philips components, Plymouth UK, this year is producing 80 lumen per
watt LEDs and next year 150L/W