LX1970IDU-TR MICROSEMI, LX1970IDU-TR Datasheet - Page 4

• Manufacturer Part Number: LX1970IDU-TR
• Manufacturer: MICROSEMI

Specifications of LX1970IDU-TR

• Lead Free Status / Rohs Status: Not Compliant

Copyright © 2007
Rev. 1.5b, 2008-01-25
L
define the light source. Nits are units for a measurement
of luminance, which is the apparent brightness of an
illuminated flat surface.
irradiance or the measurement of electromagnetic
radiation flux both visible and invisible. The first step in
the conversion process is to convert irradiance to
illuminance, which essentially involves running the
irradiant flux through a photopic filter. In normal ambient
a photopic curve is used and in dark ambient a scotopic
curve (dark adapted eye) is used. If the light is composed
of only one wavelength, a conversion chart will tell the
conversion factor to convert
If more than one wavelength is used, the light spectrum
of the irradiance must be applied to the photopic filter to
determine the resultant illuminance. The most sensitive
wavelength for the normal light adapted human eye is
555nm. At 555nm, the conversion factor is 683 Lux =
1W/m
at 555nm.
IGHT UNITS
In converting from
2
White
Figure 1 – Light Current Measurement Circuit
= 100
LED
I N T E G R A T E D
µ
W/cm
Current
Source
2
11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: [phone]
. Therefore 14.6
µ
W/cm
µ
W/cm
M E A S U R E M E N T C I R C U I T C O N F I G U R A T I O N S
µ
W/m2 to lux (lumens/m2).
2
to Nits it is necessary to
2
LX1970
P R O D U C T S
VDD
is a measurement of
µ
W/cm² = 100 lux
ISNK
A P P L I C A T I O N N O T E S
A
Analog Mixed Signal Group
ISRC
VS
A
Microsemi
illuminance to luminance. The units for illuminance are lux or
lumens/m
lumens/m
Lambertian surface which has perfect dispersion and total
reflection, the conversion from lux to nits is 3.14 lux falling on
a Lambertian reflector produces 1 Nit. Therefore 100 Lux will
produce 31.4 Nits.
produce the same output current for the same number of nits or
lux, regardless of the color of the light. However, because the
match is not perfect, there is still wavelength dependency
particularly at the ends of the visible spectrum.
520nm, however depending on the light source, what the
human eye perceives as ‘white’ light may actually be composed
of peak wavelengths of light other than 520nm. For instance a
typical fluorescent lamp includes dominant light not only near
550nm but also at 404 and 435nm. Incandescent light sources
such as standard tungsten lights generate substantial IR
radiation out beyond 2000nm.
If the photo sensor had a truly photopic response, it would
In the case of the LX1970 the peak photo response is at
The next step in the conversion process is to convert
White
LED
2
2
.
/steradian.
Figure 2 – IR sensitivity Measurement Circuit
The
P
Visible Light Sensor
Current
Sources
RODUCTION
units
Assuming the illuminance falls on a
for
D
IR LED
910nm
ATA
luminance
S
HEET
LX1970
VDD
are
LX1970
Nits
A
%
SRC
or
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