[Samsung Galaxy SL i9003] arindammanidas:
I did a test and I think I found the cause of lcd backlight issue :). Take a look at the logcat below :

LOGCAT :

D/dalvikvm( 2502): GC_EXPLICIT freed 521K, 46% free 3791K/6919K, external 2958K/
3519K, paused 81ms
[COLOR=Red][B]/**BACKLIGHT STARTS TO GO DIM HERE[/B]*/[/COLOR]
I/lights ( 2011): ********** set_light_backlight 33
I/lights ( 2011): ********** set_light_backlight 31
I/lights ( 2011): ********** set_light_backlight 30
I/lights ( 2011): ********** set_light_backlight 28
I/lights ( 2011): ********** set_light_backlight 27
I/lights ( 2011): ********** set_light_backlight 25
I/lights ( 2011): ********** set_light_backlight 23
I/lights ( 2011): ********** set_light_backlight 22
I/lights ( 2011): ********** set_light_backlight 20
I/lights ( 2011): ********** set_light_backlight 19
I/lights ( 2011): ********** set_light_backlight 17
I/lights ( 2011): ********** set_light_backlight 16
I/lights ( 2011): ********** set_light_backlight 14
I/lights ( 2011): ********** set_light_backlight 12
I/lights ( 2011): ********** set_light_backlight 11
I/lights ( 2011): ********** set_light_backlight 9
I/lights ( 2011): ********** set_light_backlight 8
I/lights ( 2011): ********** set_light_backlight 6
I/lights ( 2011): ********** set_light_backlight 5
I/lights ( 2011): ********** set_light_backlight 3
I/lights ( 2011): ********** set_light_backlight 1
I/lights ( 2011): ********** set_light_backlight 0
I/power ( 2011): *** set_screen_state 0
V/tspdrv ( 2011): opened device /dev/tspdrv
V/tspdrv ( 2011): TSPDRV_IDENTIFY_CALLER success
V/tspdrv ( 2011): TSPDRV_GET_NUM_ACTUATORS success, actuators = 1
V/tspdrv ( 2011): timeout_ms: 0
V/tspdrv ( 2011): TSPDRV_STOP_KERNEL_TIMER success
V/tspdrv ( 2011): TSPDRV_DISABLE_AMP success
D/SurfaceFlinger( 2011): About to give-up screen, flinger = 0x17c438
[COLOR=Red][B]/**SCREEN IS OFF. NO BACKLIGHT[/B]*/[/COLOR]
[COLOR=Red][B]/**NOW BACKLIGHT POPS UP!!![/B]*/[/COLOR]
[I][B]I/AlarmManager( 2011): wakelock acquire, uid:1000 at elapsed real time: 594934
I/AlarmManager( 2011): wakelock release, uid:1000 at elapsed real time: 594959[/B][/I]
D/dalvikvm( 2011): GC_CONCURRENT freed 427K, 38% free 5014K/8007K, external 0K/0
K, paused 4ms+17ms

I think the AlarmManager could be the issue :

[I][B]I/AlarmManager( 2011): wakelock acquire, uid:1000 at elapsed real time: 594934
I/AlarmManager( 2011): wakelock release, uid:1000 at elapsed real time: 594959
[/B][/I]

Another logcat :

I/lights ( 2011): ********** set_light_backlight 35
I/lights ( 2011): ********** set_light_backlight 33
I/lights ( 2011): ********** set_light_backlight 31
I/lights ( 2011): ********** set_light_backlight 30
I/lights ( 2011): ********** set_light_backlight 28
I/lights ( 2011): ********** set_light_backlight 27
I/lights ( 2011): ********** set_light_backlight 25
I/lights ( 2011): ********** set_light_backlight 23
I/lights ( 2011): ********** set_light_backlight 22
I/lights ( 2011): ********** set_light_backlight 20
I/lights ( 2011): ********** set_light_backlight 19
I/lights ( 2011): ********** set_light_backlight 17
I/lights ( 2011): ********** set_light_backlight 16
I/lights ( 2011): ********** set_light_backlight 14
I/lights ( 2011): ********** set_light_backlight 12
I/lights ( 2011): ********** set_light_backlight 11
I/lights ( 2011): ********** set_light_backlight 9
I/lights ( 2011): ********** set_light_backlight 8
I/lights ( 2011): ********** set_light_backlight 6
I/lights ( 2011): ********** set_light_backlight 5
D/dalvikvm( 2011): GC_CONCURRENT freed 587K, 39% free 4990K/8071K, external 0K/0
K, paused 8ms+13ms
I/lights ( 2011): ********** set_light_backlight 3
I/lights ( 2011): ********** set_light_backlight 1
I/lights ( 2011): ********** set_light_backlight 0
I/power ( 2011): *** set_screen_state 0
V/tspdrv ( 2011): opened device /dev/tspdrv
V/tspdrv ( 2011): TSPDRV_IDENTIFY_CALLER success
V/tspdrv ( 2011): TSPDRV_GET_NUM_ACTUATORS success, actuators = 1
V/tspdrv ( 2011): timeout_ms: 0
V/tspdrv ( 2011): TSPDRV_STOP_KERNEL_TIMER success
V/tspdrv ( 2011): TSPDRV_DISABLE_AMP success
D/SurfaceFlinger( 2011): About to give-up screen, flinger = 0x17c438
[COLOR=Red][B]/**NOW BACKLIGHT POPS UP!!![/B]*/[/COLOR]
[COLOR=Purple][B][I]I/AlarmManager( 2011): wakelock acquire, uid:1000 at elapsed real time: 1385621
I/AlarmManager( 2011): wakelock release, uid:1000 at elapsed real time: 1385646
I/AlarmManager( 2011): wakelock acquire, uid:1000 at elapsed real time: 1393633
I/AlarmManager( 2011): wakelock release, uid:1000 at elapsed real time: 1393716
I/AlarmManager( 2011): wakelock acquire, uid:1000 at elapsed real time: 1453633
I/AlarmManager( 2011): wakelock release, uid:1000 at elapsed real time: 1453715[/I][/B][/COLOR]

Here is the AlarmDump :

Current Alarm Manager state:
Realtime wakeup (now=2012-01-21 09:42:14):
RTC_WAKEUP #1: Alarm{406f3f18 type 0 com.android.providers.calendar}
type=0 when=+21h56m34s101ms repeatInterval=0 count=0
operation=PendingIntent{406d6cf8: PendingIntentRecord{4074d240 com.android.providers.calendar broadcastIntent}}
RTC_WAKEUP #0: Alarm{4069c5d8 type 0 com.google.android.gsf}
type=0 when=+10m41s573ms repeatInterval=1800000 count=0
operation=PendingIntent{406d2f38: PendingIntentRecord{406d5c20 com.google.android.gsf broadcastIntent}}
RTC #1: Alarm{40681930 type 1 android}
type=1 when=+14h17m45s521ms repeatInterval=0 count=0
operation=PendingIntent{4064f7d8: PendingIntentRecord{4060ef08 android broadcastIntent}}
RTC #0: Alarm{406d8e30 type 1 android}
type=1 when=+45s521ms repeatInterval=0 count=0
operation=PendingIntent{4062e2b0: PendingIntentRecord{4066eea8 android broadcastIntent}}
Elapsed realtime wakeup (now=+5m35s166ms):
ELAPSED #1: Alarm{40646828 type 3 android}
type=3 when=+6m48s447ms repeatInterval=0 count=0
operation=PendingIntent{4055f380: PendingIntentRecord{406c7a00 android broadcastIntent}}
ELAPSED #0: Alarm{4070e7b8 type 3 com.android.vending}
type=3 when=+5m36s536ms repeatInterval=86400000 count=0
operation=PendingIntent{4070f160: PendingIntentRecord{4070e6e0 com.android.vending broadcastIntent}}

[COLOR=Red][B]Alarm Stats:
android
229ms running, 3 wakeups
3 alarms: act=com.android.internal.policy.impl.PhoneWindowManager.DELAYED_KEYGUARD flg=0x4
5 alarms: act=android.intent.action.TIME_TICK flg=0x40000004[/B][/COLOR]